Antenatal screening and predicting hypertension in pregnancy for midwives

Introduction 

The cause of hypertension in pregnancy remains unknown and results in an increased risk of complications for mother and baby.1 The Society of Obstetric Medicine of Australia and New Zealand (SOMANZ) classify hypertension in pregnancy as pre-eclampsia (PE), eclampsia, gestational hypertension (GH), and chronic hypertension. Defined as a disorder that combines hypertension with or without proteinuria, PE involves one or more organ system whereas GH is the onset of hypertension after 20 weeks gestation without organ involvement and returns to normal within 3 months of delivery.2 Although much is known of predisposing factors for hypertension in pregnancy, screening is limited to measurement of blood pressure (BP) reading with further investigations undertaken if PE or GH is suspected. Symptoms of developing PE, such as an elevated BP, can be vague and singular.

A number of systematic reviews published on the screening and prevention of PE identify a core group of factors that can be used to predict and subsequently help prevent this disease. However, these reviews have largely addressed medical practice. As midwifery-based antenatal care becomes an increasingly prevalent choice for healthy low-risk women,3 prediction and the early diagnoses of PE becomes more important, particularly in remote areas or in clinics without access to medical staff.

The purpose of this literature review is to evaluate research investigating antenatal screening practices which fall within the midwife's scope of practice as defined by the Australian Nursing and Midwifery Council's National Competency Standards and the Australian College of Midwives’,4 National Midwifery Guidelines for Consultation and Referral.5

Literature search strategy and databases searched 

An electronic database search was performed using Medline, Pub Med, CINAHL, Ebscohost, and Scopus and the Boolean strategy. Keywords used singularly and in combination included: pre-eclampsia; screening; trimester (1st and 2nd); pregnancy; blood pressure; tests; induced hypertension; pregnancy-induced hypertension; toxaemia; risks; antenatal; and midwives/midwife.

The search strategy involved a three-phase approach. Initially, criteria for inclusion were primary research, published in English language, in peer reviewed journals within the previous 20 years where the population under study was pregnant, with reported outcomes of prevention, screening or prediction of hypertension in pregnancy. A large number of papers (n=201) were identified under the initial search terms. A preliminary review of these studies revealed that many focused on risk factors, published guidelines and policies, and populations of high-risk women or women with already diagnosed PE (n=42) and these were subsequently excluded.

The remaining papers underwent secondary screening, and analysis. Although midwives can refer and implement screening tests, the diagnoses and interpretation of specific results including Doppler ultrasonography, and complex haematological changes remains outside the midwives current scope of practice. Those papers involving research outcomes based on the use of Ultrasonography, predictors based on pathology testing and results, and physical assessment and testing determined by a medical practitioner were subsequently excluded (n=146). Table 2 summarises studies excluded in this second phase.

Thirty-three papers which reflected the scope of midwifery care practice remained and have been included in this third phase of review (Table 1). Factors which increase the risk of GH and PE have been identified from existing literature and are recognised by SOMANZ (2008). They can be used by midwives in practice. These include: nulliparity; age greater than (>) 40 years; family history of PE in a mother or sister; previous PE; Body Mass Index (BMI)>25; multiple pregnancies; pre-existing diabetes; and diastolic BP measurement greater than 80mmHg at the initial antenatal visit. The analysis indicated evidence of modifiable, non-modifiable and clinical assessment factors which may be included in a midwifery model that predicts PE.

Table 1. Included research studies and literature reviews.

	Included study	Study design	Sample size	Title
	Modifiable factors
	Duckitt (2005)	Systematic review	52 studies	Risk factors for preeclampsia at antenatal booking
	Meher (2006)	Systematic review	1 study	Garlic for preventing pre-eclampsia and its complications
	Hofmeyer (2007)	Systematic review	12 studies	Dietary Calcium supplementation for prevention of pre-eclampsia and related problems
	Cnossen (2007)	Bivariate meta analysis	36 studies	Accuracy of body mass index in predicting pre-eclampsia
	Olsen (2000)	RCT	1,647 patients from 19 hospitals in Europe	Randomised clinical trials of fish oil supplementation in high risk pregnancies
	Kumar (2009)	RCT	524 participants from India	Calcium supplementation for prevention of pre-eclampsia
	Rumbold (2006)	RCT	1,877 participants in multicentre Australian trial	Vitamins C and E and risks of preeclampsia and perinatal complications
	Poston (2006)	RCT	2,410 participants from 25 hospitals	Vitamin C and Vitamin E in pregnant women at risk for pre-eclampsia
	Mamun (2005)	Cohort study	2,934 participants (children)	Family and early life factors associated with changes in overweight status between ages 5 and 14 years
	Belogolovkin (2007)	Cohort study	29,268 participants from a multicentre study	The effect of low body mass index on the development of gestational hypertension and preeclampsia
	Oken (2007)	Cohort study	1,718 participants form USA	Diet during pregnancy and risk of preeclampsia or gestational hypertension
	Triche (2008)	Cohort study	2,291 participants in USA	Chocolate consumption in pregnancy and reduced likelihood of preeclampsia
	Theroux (2007)	Cohort study	1,835 participants in USA	Preventing pre-eclampsia, do vitamins work?
	Osterdal (2009)	Cohort study	85,139 participants in Denmark	Does leisure time physical activity in early pregnancy protect against pre-eclampsia?
	Ruma (2008)	Cohort study	775 participants in USA	Maternal periodontal disease, systemic inflammation, and risk for preeclampsia
	Pick (2005)	Cohort study	101 participants from USA	Assessment of diet quality in pregnant women using the healthy eating index
	Non-modifiable factors
	Trogstad (2008)	Cohort study	20,846 participants in Norway	Previous abortions and risk of pre-eclampsia
	Trogstad (2009)	Cohort study	20,846 participants in Norway	The effect of recurrent miscarriage and infertility on the risk of pre-eclampsia
	Mostello (2008)	Cohort study	103,860 participants from birth certificate	Recurrence of pre-eclampsia: effects of gestational age at delivery of the first pregnancy, BMI, paternity, and interval between births
	Caughey (2005)	Retrospective cohort study	127,544 participants from linked data in USA	Maternal ethnicity, paternal ethnicity, and paternal ethnic discordance
	Carr (2005)	Case–control study	10,723 participants using linked data in USA	A sister's risk: family history as a predictor of preeclampsia
	Silva (2008)	Cohort study	3,547 women in the Netherlands	Low socioeconomic status is a risk factor for preeclampsia: the generation R study
	Carvalho (2006)	Cohort study	29 participants in Brazil	Predictive factors for pregnancy hypertension in primiparous adolescents
	Clinical assessment
	Conde-Agudelo (2004)	Systematic review	87 studies	Screening
	Cnossen (2008)	Systematic review	34 studies	MAP
	Miller (2007)	Cohort study	1,655 participants for Sweden and USA	First trimester mean arterial pressure and risk of preeclampsia
	The HAPO Study Cooperative Research Group (2008)	Observational cohort	23,316 participants from 16 international multicentres	Hyperglycaemia and adverse pregnancy outcomes
	Tomoda (1994)	Cohort study	125 participants form Japan	Prediction of pregnancy-induced hypertension by isometric exercise
	Baker (1994)	Cohort study	200 participants from UK	The use of the hand grip test for predicting pregnancy induced hypertension
	Watson (1995) (Meher and Duley, 2006)	Cohort study	97 participants from USA	Pressor response to cycle ergometry in the midtrimester of pregnancy: can it predict preeclampsia?

Abbreviations: BMI, Body Mass Index; RCT, Random Controlled Trial; MAP, Mean Arterial Pressure.

Table 2. Excluded studies.

	Excluded studies	Study design	Sample size	Title
	Ultrasonography
	Arduini (1987)	Experimental trial	3,359 pregnancies	Utero-placental blood flow velocity waveforms as predictors of pregnancy-induced hypertension
	Atkinson (1994)	Prospective screening study	3,107 pregnancies	The predictive value of umbilical artery Doppler studies for preeclampsia or fetal growth retardation in a preeclampsia prevention trial
	Audibert (2005)	Cohort, observational	3,058 pregnancies	Prediction of preeclampsia or intrauterine growth restriction by second trimester serum screening and uterine Doppler velocimetry
	Bower (1994)	Prospective screening study	210 pregnancies	Doppler ultrasound screening as part of routine antenatal scanning: prediction of pre-eclampsia and intrauterine growth retardation
	Cobellis (2006)	Intervention cohort	4,293 pregnancies	Mid-trimester fetal-placental velocimetry response to nifedipine may predict early the onset of pre-eclampsia. 1
	Dept of Obstetric and Gynaecology, Akita	Intervention cohort	93 pregnancies	A study for predicting toxaemia of pregnancy by the diastolic notch in pulsed Doppler flow velocity waveforms of the uterine arteries—quantitative analysis of the diastolic notch as uterine arterial index (UTAI)]
	Deurioo (2007)	Prospective screening study	433 pregnancies	Colour Doppler ultrasound of spiral artery blood flow for prediction of hypertensive disorders and intra uterine growth restriction: a longitudinal study
	De Paco (2008)	Experimental trial	60 pregnancies	Maternal cardiac output between 11 and 13 weeks of gestation in the prediction of preeclampsia and small for gestational age
	Espinoza (2007)	Prospective cohort	534 women	Identification of patients at risk for early onset and/or severe preeclampsia with the use of uterine artery Doppler velocimetry and placental growth factor. 1
	Florio (2005)	Prospective screening study	166 women	Factor II: C activity and uterine artery Doppler evaluation to improve the early prediction of pre-eclampsia on women with gestational hypertension
	Gudnasson (2004)	Prospective screening study	878 women	Preeclampsia—abnormal uterine artery Doppler is related to recurrence of symptoms during the next pregnancy
	Jacobson (1990)	Intervention cohort	93 participants from UK	The value of Doppler assessment of the uteroplacental circulation in predicting preeclampsia or intrauterine growth retardation
	Khalil (2009)	Cohort, observational	3,348 women	Pulse wave analysis: a preliminary study of a novel technique for the prediction of pre-eclampsia
	Khaw (2008)	Prospective observational cohort	534 participants from UK	Maternal cardiac function and uterine artery Doppler at 11–14 weeks in the prediction of pre-eclampsia in nulliparous women
	Melchiorre (2008)	Intervention cohort	93 pregnancies	First-trimester uterine artery Doppler indices in term and preterm pre-eclampsia
	Mirpuri (2001)	Prospective screening study	108 women	High-frequency ultrasound imaging of the skin during normal and hypertensive pregnancies
	Nicolaides (2006)	Nested case control study	124 women	A novel approach to first-trimester screening for early pre-eclampsia combining serum PP-13 and Doppler ultrasound
	Onwudiwe (2008)	Cohort, observational	65 women	Prediction of pre-eclampsia by a combination of maternal history, uterine artery Doppler and mean arterial pressure
	Parra (2005)	Experimental trial	570 women	Screening test for preeclampsia through assessment of uteroplacental blood flow and biochemical markers of oxidative stress and endothelial dysfunction
	Phupong (2003)	Cohort, observational	540 women	Predicting the risk of preeclampsia and small for gestational age infants by uterine artery Doppler in low-risk women
	Pilalis (2007)	Prospective cohort	565 women	Screening for pre-eclampsia and fetal growth restriction by uterine artery Doppler and PAPP-A at 11–14 weeks gestation
	Plasencia (2008)	Intervention cohort	2,430 women	Uterine artery Doppler at 11+0 to 13+6 weeks and 21+0 to 24+6 weeks in the prediction of pre-eclampsia
	Riskin-Mashiah (2002)	Prospective screening study	93 pregnancies	Transcranial Doppler measurement of cerebral velocity indices as a predictor of preeclampsia
	Torricelli (2006)	Intervention cohort	20 pregnancies	Low-molecular-weight heparin improves the performance of uterine artery Doppler velocimetry to predict preeclampsia and small-for-gestational age infant in women with gestational hypertension
	Tranquilli (2007)	Prospective screening study	433 pregnancies	The relative weight of Doppler of the uterine artery and 24-h ambulatory blood pressure monitoring in predicting hypertension in pregnancy and preeclampsia
	Yu (2005)	Prospective screening study	2,615 pregnancies	An integrated model for the prediction of preeclampsia using maternal factors and uterine artery Doppler velocimetry in unselected low-risk women
	Pathology
	Bahado-Singh (2002)	Intervention cohort	568 participants from USA	The role of hyperglycosylated hCG in trophoblast invasion and the prediction of subsequent pre-eclampsia
	Baker (1992)	Cohort, observational	34 participants from UK	Comparative study of platelet angiotensin II binding and the angiotensin II sensitivity test as predictors of pregnancy-induced hypertension
	Baumann (2008)	Cohort, observational	148 participants from Switzerland	First-trimester serum levels of soluble endoglin and soluble fms-like tyrosine kinase-1 as first-trimester markers for late-onset preeclampsia
	Buhimschi (2008)	Prospective screening study	284 participants from USA	Proteomic profiling of urine identifies specific fragments of SERPINA1 and albumin as biomarkers of preeclampsia
	Chafetz (2007)	Prospective screening study	425 participants from Israel	First-trimester placental protein 13 screening for preeclampsia and intrauterine growth restriction
	D’Anna (2008)	Prospective screening study	144 participants from Italy	Second trimester neutrophil gelatinase-associated lipocalin as a potential prediagnostic marker of preeclampsia
	Davidson (2003)	Retrospective cohort	225 participants from Scotland	Maternal serum activin, inhibin, human chorionic gonadotrophin and alpha-fetoprotein as second trimester predictors of pre-eclampsia
	De Vivo (2008)	Cohort, observational	104 participants from Italy	Endoglin, PlGF and sFlt-1 as markers for predicting pre-eclampsia
	Dreyfus	Intervention cohort		The prediction of preeclampsia: reassessment of clinical value of increased plasma levels of fibronectin
	Florio (2004)	Prospective screening study	58 participants from Italy	The measurement of maternal plasma corticotropin-releasing factor (CRF) and CRF-binding protein improves the early prediction of preeclampsia
	Ghorashi (2008)	Nested case control study	40 participants from Iran	The relationship between serum concentration of free testosterone and pre-eclampsia
	Gonen (2008)	Intervention cohort	1,366 women from Israel	Placental protein 13 as an early marker for pre-eclampsia: a prospective longitudinal study
	Gredmark (1999)	Intervention cohort	657 participants from Sweden	Total fibronectin in maternal plasma as a predictor for preeclampsia
	Ho (1992)	Intervention cohort	66 participants from Taiwan	The predictive value of the homeostasis parameters in the development of preeclampsia
	Hogg (2000)	RCT	437 participants from UK	Second-trimester plasma homocysteine levels and pregnancy-induced hypertension, preeclampsia, and intrauterine growth restriction
	Jones (1996)	Cohort, observational	238 participants from Australia	Fibronectin as a predictor of preeclampsia: a pilot study
	Konijnenberg (1997)	Prospective screening study	244 participants from The Netherlands	Can flow cytometric detection of platelet activation early in pregnancy predict the occurrence of preeclampsia? A prospective study
	Kyle (1995)	RCT	495 participants from UK	The angiotensin sensitivity test and low-dose aspirin are ineffective methods to predict and prevent hypertensive disorders in nulliparous pregnancy
	Lambert-Messerlain (2000)	Retrospective cohort	360 participants from USA	Second-trimester levels of maternal serum human chorionic gonadotropin and inhibin a as predictors of preeclampsia in the third trimester of pregnancy
	Leal (2009)	Prospective screening study	697 participants from UK	First-trimester maternal serum tumour necrosis factor receptor-1 and pre-eclampsia
	Levine (2005)	Nested case control study	240 participants from USA	Urinary placental growth factor and risk of preeclampsia
	Levy (2007)	Intervention cohort	103 participants from West Indies	Booking blood pressures and plasma nitrite in Jamaican women with pre-eclampsia
	Livingstone (2001)	Nested case control study	880 participants from USA	Placenta growth factor is not an early marker for the development of severe preeclampsia
	Lynch (2008)	Observational cohort	701 participants from USA	Alternative complement pathway activation fragment Bb in early pregnancy as a predictor of preeclampsia
	Madazli (2005)	Prospective screening study	122 participants fro Turkey	Prediction of preeclampsia with maternal mid-trimester placental growth factor, activin A, fibronectin and uterine artery Doppler velocimetry
	Margarit (2005)	Prospective observational cohort	96 women from Greece	Second trimester amniotic fluid endothelin concentration. A possible predictor for pre-eclampsia
	Mello (2002)	Longitudinal study	187 participants from Italy	Individual longitudinal patterns in biochemical and haematological markers for the early prediction of pre-eclampsia
	Meyers (2007)	Case control	74 participants from USA	Evidence for multiple circulating factors in preeclampsia
	Moore Simas (2007)	Prospective screening study	94 participants from USA	Angiogenic factors for the prediction of preeclampsia in high-risk women
	Muller (1996)	Cohort, observational	5,776 participants from North America	Maternal serum human chorionic gonadotropin level at fifteen weeks is a predictor for preeclampsia
	O’Brien (1999)	Prospective cohort	325 participants from UK	Failure of platelet angiotensin II binding to predict pregnancy-induced hypertension
	Ong (2001)	Prospective screening study	668 participants from UK	First-trimester maternal serum levels of placenta growth factor as predictor of preeclampsia and fetal growth restriction
	Osmanagaoglu (2005)	Intervention cohort	85 participants from Turkey	Coagulation inhibitors in preeclamptic pregnant women.
	Parretti (2006)	Intervention cohort	829 participants from Italy	Preeclampsia in lean normotensive normotolerant pregnant women can be predicted by simple insulin sensitivity indexes
	Poon (2008)	Prospective cross-sectional observational study	2,679 participants from UK	Urine albumin concentration and albumin-to-creatinine ratio at 11(+0) to 13(+6) weeks in the prediction of pre-eclampsia
	Poon (2009)	Prospective screening study	8,141 participants from UK	First-trimester maternal serum pregnancy-associated plasma protein-A and pre-eclampsia
	Poston (2006)	RCT	2,410 participants from 25 hospitals	Vitamin C and vitamin E in pregnant women at risk for pre-eclampsia (VIP trial): randomised placebo-controlled trial
	Pouta (1998)	Prospective screening study	1,037 participants from Finland	Midtrimester N-terminal proatrial natriuretic peptide, free beta hCG, and alpha-fetoprotein in predicting preeclampsia
	Purwosunu (2009)	Intervention cohort	372 participants from Japan	Prediction of preeclampsia by analysis of cell-free messenger RNA in maternal plasma
	Raty (1999)	Prospective screening study	4,356 participants from Finland	Prediction of pre-eclampsia with maternal mid-trimester total renin, inhibin A, AFP and free beta-hCG levels. 1
	Rodgers (2006)	Prospective observational cohort	381 participants from Hong Kong	Oxidative stress in midpregnancy as a predictor of gestational hypertension and pre-eclampsia
	Roiz-Hernandez (2006)	Prospective cohort	784 participants from Mexico	Human chorionic gonadotropin levels between 16 and 21 weeks of pregnancy and prediction of pre-eclampsia
	Romero (2008)	Case control	350 participants from USA	First-trimester maternal serum PP13 in the risk assessment for preeclampsia
	Rudra	Nested case control study	733 participants from Sweden	A prospective study of early-pregnancy plasma malondialdehyde concentration and risk of preeclampsia
	Salako (2003)	Prospective screening study	100 participants fro Nigeria	Microalbuminuria in pregnancy as a predictor of preeclampsia and eclampsia
	Shaarawy (2000)	Prospective screening study	80 participants from Egypt	Plasma endothelin-1 and mean arterial pressure in the prediction of pre-eclampsia
	Shaarawy (2001)	Intervention cohort	155 participants from Egypt	The clinical value of microtransferrinuria and micro albuminuria in the prediction of pre-eclampsia
	Song (2004)	Intervention cohort	132 pregnancies from China	Predicting pregnancy-induced hypertension with dynamic hemodynamics
	Stepan (2008)	Prospective observational cohort	77 participants from Germany	Circulatory soluble endoglin and its predictive value for preeclampsia in second-trimester pregnancies with abnormal uterine perfusion
	Thornton (1989)	Cohort, observational	400 participants from UK	A prospective study of haemostatic tests at 28 weeks gestation as predictors of pre-eclampsia and growth retardation
	Vaillant (1996)	Prospective screening study	434 participants from France	Validity in nullipara's of increased beta-human chorionic gonadotrophin at mid-term for predicting pregnancy-induced hypertension complicated with proteinuria and intrauterine growth retardation
	Vattern (2007)	Nested case control study	746 participants from Norway	Changes in circulating level of angiogenic factors from the first to second trimester as predictors of preeclampsia
	Vattern (2008)	Case control	29,948 participants from Norway	Changes in circulating level of IGF-I and IGF-binding protein-1 from the first to second trimester as predictors of preeclampsia
	Wald (2006)	Nested case control study	480 participants in UK	Screening in early pregnancy for pre-eclampsia using Down syndrome quadruple test markers
	Waller (1996)	Retrospective cohort	51,008 participants via medical records in USA	The association between maternal serum alpha-fetoprotein and preterm birth, small for gestational age infants, preeclampsia, and placental complications
	Woolcock (2008)	Cohort, observational	39 from NSW	Soluble Flt-1 as a diagnostic marker of pre-eclampsia
	Yie (2005)	Intervention cohort	24 participants from Canada	Low plasma HLA-G protein concentrations in early gestation indicate the development of preeclampsia later in pregnancy
	Physical assessment
	Brown (2001)	Intervention cohort	122 participants from Australia	Twenty-four-hour automated blood pressure monitoring as a predictor of preeclampsia
	Easterling (1999)	RCT	56 participants from USA	Prevention of preeclampsia: a randomized trial of atenolol in hyperdynamic patients before onset of hypertension
	Eneroth-Grimfors (2008)	Experimental trial	40 participants from Sweden	Evaluation of three simple physiologic tests as predictors of pregnancy-induced hypertension. A pilot study
	Hermida (1998)	Prospective screening study	152 participants from Spain	Blood pressure excess for the early identification of gestational hypertension and preeclampsia
	Hermida (2001)	Prospective screening study	328 participants from Spain	Evaluation of the blood pressure load in the diagnosis of hypertension in pregnancy
	Higgins (1997)	Intervention cohort	1,102 participants from Ireland	Can 24-hour ambulatory blood pressure measurement predict the development of hypertension in primigravidae?
	Innes (1999)	Retrospective cohort	4,440 participants from USA	A woman's own birth weight and gestational age predict her later risk of developing preeclampsia, a precursor of chronic disease
	Kazerooni (2006)	Prospective screening study	102 participants in Iran	Second trimester cardiac output and its predictive value for preeclampsia
	Martin (1999)	Retrospective cohort	970 participants from USA	Early risk assessment of severe preeclampsia: admission battery of symptoms and laboratory tests to predict likelihood of subsequent significant maternal morbidity
	Mikolajczk (2008)	Retrospective cohort	533 participants from USA birth records	Effects of interpregnancy interval on blood pressure in consecutive pregnancies
	Moretti (2004)	Intervention cohort	124 participants from USA	Increased breath markers of oxidative stress in normal pregnancy and in preeclampsia
	Ohkuchia (2006)	Cohort, observational	1,518 participants from Japan	Normal and high-normal blood pressures, but not body mass index, are risk factors for the subsequent occurrence of both preeclampsia and gestational hypertension: a retrospective cohort study
	Ramon (2000)	Experimental trial	202 participants from Spain	Blood pressure patterns in normal pregnancy, gest hypertension+preeclampsia
	Romero-Gutierrez (2004)	Prospective screening study	160 participants from Mexico	Homeostatic model assessment and risk for hypertension during pregnancy: a longitudinal prospective study
	Spinapolice (1998)	Experimental trial	32 participants from USA	Effective prevention of Gestational hypertension in Nulliparous women at high risk as identified by the rollover test
	Stamillio (2000)	Retrospective cohort	1,998 participants from USA medical records	Can antenatal clinical and biochemical markers predict the development of severe preeclampsia?
	Takase (2003)	Prospective screening study	43 participants from Japan	Flow-mediated dilation in brachial artery in the second half of pregnancy and prediction of pre-eclampsia. 1
	Urdzik (2007)	Retrospective cohort	578 participants from Czech Republic	Prediction of preeclampsia using the integrated test markers
	Verwoerd (2002)	Case control	110 participants from South Africa	Primipaternity and duration of exposure to sperm antigens as risk factors for pre-eclampsia
	Watson (1995)	Intervention cohort	97 participants from USA	Pressor response to cycle ergometry in the midtrimester of pregnancy: can it predict preeclampsia?
	Yamamoto (2001)	Cohort, Observational	224 participants from Japan	Waist to hip circumference ratio as a significant predictor of preeclampsia, irrespective of overall adiposity

Modifiable factors 

A modifiable risk factor is one that can be altered with intervention thereby decreasing the risk of the complication it causes. Midwives are at the forefront of information gathering and using thorough history taking and accurate assessment can identify potential risk factors. The accuracy of this information is vital to allow the clinician to formulate and provide optimal individualised care for mother and baby.

High BMI and its association with PE has been documented in a systematic review of the risk factors for PE identified during antenatal booking with a BMI>35kg/m2 found to double the risk of developing PE.6 Cnossen et al. performed a bivariate meta-analysis to determine the ability of BMI to predict PE.7 BMI (calculated from both self-reported or first booking height and weight) although helpful, was not useful as a single predictive factor. While reporting bias may be a consideration in this approach, the work of Mamun et al. demonstrates a strong correlation between the accuracy of self-reported and booking BMI,8 suggesting the clinician is able to accept either measurement.

A longitudinal study evaluated the relationship between low BMI in first trimester and the incidence of PE and GH compared with normal and high BMI.9 Women with a BMI<19.8kg/m2 had less incidence of GH and PE. However, the cohort of low BMI women were found to be younger therefore less likely to have underlying conditions that predispose to PE. The author offers that this may be due to the absence of metabolic disorders which can manifest with increasing BMI and the association of other complications such as increased incidence of intrauterine growth retardation.

Women often seek advice from midwives regarding diet, vitamins and exercise during pregnancy in order to establish and maintain a healthy lifestyle for themselves and their babies. To offer the best advice, midwives must practice from an evidence-based perspective by being aware of all current literature relating to this facet of antenatal care.

Studies which examine diet vary in their methodological approaches and quality. A systematic review on the use of garlic for prevention of PE and its complications10 did not provide an adequate evidence base to be able to recommend increased garlic intake during pregnancy. The premise that garlic may lower blood pressure therefore preventing uterine constriction associated with PE is an area requiring further study.

A prospective cohort study (n=1718) examined the association of a number of vitamins, fatty acids and calcium with the development of PE using a food frequency questionnaire in the first trimester.11 No significant association for any particular diet component was reported however, a potential benefit of a regular intake of oily fish (n−3 fatty acids) was identified. This was in contrast to a large randomised trial which concluded that fish oil had no effect on hypertension in pregnancy.12

A further study involving food in pregnancy examined chocolate consumption in early pregnancy and its effect on PE incidence.13 The authors acknowledge that their results may suggest chocolate consumption decreases the risk of PE however; the evidence is not strong enough make public health recommendations due in part to the possibility of under and over-reporting of chocolate consumption by the participants through self-reported questionnaires.

Midwives are often asked for advice during the course of antenatal care regarding vitamins and mineral use in pregnancy. The role of calcium in reducing the incidence of PE has been reported in a number of research studies detailed in a Cochrane review.14 It was concluded that adequate dietary calcium in early pregnancy should be encouraged and that supplementation appears to reduce the risk of PE. One study concluded calcium supplements reduced the incidence of PE where dietary intake of calcium was below recommended levels.15 This is relevant to midwifery practice when an observational study has shown that pregnant women may not be receiving the recommended intake of calcium through diet alone.16

Two randomised controlled trials proposed that Vitamins C and E reduced the risk of PE17, 18 although neither proved this to be the case. One study reported Vitamin C and E increased the rate of low birth weight babies18 while Theroux sought to assess the association between PE pre-conception multivitamin use finding further research was required as the results were inconclusive.19

Advice regarding exercise and general well-being has long been a part of midwifery care to promote positive maternal and baby outcomes. One study examined physical activity and another oral health; both being aspects of health care that midwives can address with their clients. Osterdal et al. investigated whether physical activity in early pregnancy decreases the risk of PE reporting there was no protective effect observed. Their data demonstrated physical activity in excess of 270min/week could increase the risk of developing PE.20 Oral hygiene was researched to investigate if it could be classed as a risk factor for PE with results showing that periodontal disease with systemic inflammation, measured as C-reactive protein, is associated with increased incidence of PE.21

These modifiable risk factors have the ability to be altered before and during a pregnancy by the women following advice, education and support from the midwife providing antenatal care.

Non-modifiable factors 

Non-modifiable risk factors cannot be altered as they are reliant on external factors such as family history, previous pregnancies, age and ethnicity. Midwives are able to identify these factors during the compilation of the patient's history, providing an opportunity to form an accurate assessment of their patient.

Trogstad et al. aimed to estimate the risk of PE in primiparous women with history of spontaneous and induced abortions.22 This observational research surveyed 20,846 women participating in the Norwegian Mothers and Child study. After adjusting for confounders, results showed that two or more induced abortions provide similar protection from PE to that of one previous pregnancy without PE. Concurrent research on the same cohort further investigated if recurrent miscarriage and infertility contributed to PE.23 Information regarding PE was compared with that of the Norwegian Birth registry and concluded that, when combined, the risk factors for infertility and recurrent miscarriages may contribute to the development of PE. The exposure data for these studies was based on self-reported questionnaires. However, this method of data collection is prone to under and over-reporting of conditions. Some of the criticisms of this method are confusion in participant's responses due to understanding of data required and reluctance of participants to disclose sensitive information.

Mostello et al. aimed to research the incidence of PE recurrence by examining the gestational age at delivery of the first pregnancy, BMI, paternity (defined as paternal status unknown or different from previous pregnancy) and birth interval in a large population-based cohort study (n=103,860). Linked by maternal name and date of birth, data from birth and fetal death certificates24 were studied. Increasing BMI and early delivery of previous pregnancies complicated by PE both contributed to its risk of recurrence however, there was no increased risk identified with change in paternal status. The limitations in the methodology of the study include the possible lack of consistency in data input. The death certificates could not include severity of pre-eclampsia and the possibility of under-reporting of underlying medical conditions which could contribute to PE were recognised by the researchers.24

During initial antenatal interview with the midwife, information is collected relating to the women's ethnicity. This information was examined using parental ethnicity and discordance to determine the association between these factors and PE.25 The retrospective cohort study (n=127,544) showed a decrease in the rate of PE in populations with Asian paternity. In Australia in 2006–2007, over 25% of immigrants were from Asian countries, making parental ethnicity an important component of the antenatal history.2

Family history is another integral part of the interview. A systematic review examined whether a medical history of PE in mothers and sisters led to a predisposition to PE.6 Inclusion of familial history questions was supported by a large population-based case–control study (n=10,723),26 which reported women who developed PE were 2.3 times more likely to have a sister who also developed PE. However, this association may be confounded by behavioural factors such as obesity and smoking that might cluster in families.27 Another smaller study (n=368) discovered that in primigravida, a family history of PE is associated with a four-fold risk of severe PE.39

Economic status is an area not necessarily assessed by midwives unless it is an issue evident for the women they care for. A cohort study examined whether low socioeconomic status as a risk factor for PE. Using educational level as an indicator of socioeconomic status,28 results showed that women in the lower socioeconomic group were more likely to develop PE. However, this finding should be interpreted cautiously. Although the response rate was 68%, lower educated women were less likely to respond. Additionally, the use of a self-reported questionnaire may have contributed to differing interpretations of educational status by participants. The conclusions demonstrated a correlation between low socioeconomic status and PE however, these phenomena were largely unexplained, so further exploration of any association is needed.

Carvallo et al. performed a small study (n=29) to examine predictive factors in adolescents (16–19 years) and the development of PE.29 Results showed the best predictors of this condition were family history and diastolic blood pressure measurements at differing periods of the day, however further research with a larger cohort is needed to verify these results.

These factors are unable to be altered during pregnancy; however reinforcement of their importance during the antenatal period can be stressed by midwives. This information, in combination with both modifiable and clinical assessment factors can be used to help identify patients at higher risk of developing PE.

Clinical assessment 

In 2004, the World Health Organisation conducted a systematic review assessing all tests used to prediction PE, and found that there is no definitive, low-cost, predictive test available.30 Another extensive systematic review highlighted numerous risk factors for hypertension in pregnancy however; many screening strategies such as the presence of antiphospholipid antibodies and interpreting Doppler-based measurements are beyond the current scope of practice of the midwife. Most recognised risk factors which contribute to PE would result in the pregnancy being categorised as “high-risk”—which, according to National Midwifery Guidelines for Consultation and Referral, would require obstetric-led antenatal care. Hence, this is beyond the scope of practice of the midwife.6

Blood pressure measurement remains one of the most definitive predictors of PE and is a key component of antenatal assessment at each visit.31 Duckitt reviewed four studies, all examining BP readings, and concluded that a systolic blood pressure of >130 doubled the risk of PE. Additionally, this review also showed that initial or booking BP was a vital component to give insight to prediction of PE.6 The gold standard of measurement of blood pressure is the mercury sphygmomanometers2, 38; however standardised practice should be employed by practitioners to avoid possible inaccurate readings. “The woman should be seated comfortably with her legs resting on a flat surface. The systolic blood pressure is accepted as the first sound heard and the diastolic blood pressure the disappearance of sounds completely. Correct cuff size is important for accurate blood pressure recording, with a larger cuff used if the upper arm circumference is greater than 33cm” [2, p. 4].

If automated devises are used then it is vital that they are checked and calibrated at least monthly to maintain accuracy and used according to manufacturer's specifications. A large international research project which was reliant on BP measurement by automatic machines in sixteen centres alleviated the potential for inconsistency by providing each centre with an identical machine, with monthly checking by the research team with mercury sphygmomanometers to detect any discrepancies in values.31

A retrospective cohort study examined if the combination of BMI and high-normal BP can be used as a predictor.32 The results showed that being overweight or obese may not be an independent risk factor for development of PE compared with just having high-normal BP; however, this study noted that further research is necessary before conclusions can be made.

A systematic review and meta-analysis was completed on the accuracy of mean arterial pressure (MAP) and BP measurements and their predictive qualities, and found that the MAP was a better predictor than BP alone.33 MAP could therefore be used by midwives during their routine antenatal care. Miller et al. used a prospective cohort (n=1655) and found that although first trimester MAP is strongly associated with increased risk of developing PE, it will not predict with accuracy those women who will develop PE.34 Cnossen et al. in their systematic review of 34 studies (n=60,599) explored the accuracy of using systolic/diastolic BP, mean BP, and increasing BP to predict PE and found that MAP was in fact a better predictor. Further research is recommended to develop algorithms that combine all predictive factors in order to identify women who will develop PE.33

A large research study (n=25,505) recently examined the effects of maternal glucose levels and adverse outcomes.31 They found that there was an association with glucose levels lower than the diagnostic level for diabetes and the incidence of PE in both fasting and 2h results.

Research by several authors relating to physical testing of hand grip and BP response to exercise has been conducted to attempt to predict PE using non-invasive interventions. Tomoda tested women by a use of a hand grip test by measurement of systolic pressure,35 Baker by hand grip alone,36 and Watson by aerobic exercise to increase heart beat up to 140beats/min.37 Although these tests are able to be performed within the midwives’ scope of practice, the reliability of operator, the amount of time required and unpredictable nature of the test does not lend itself to introduction to routine testing.

Accurate clinical assessment is essential to provide ongoing antenatal care in the second and third trimester. Midwives may be able to assess all facets of the antenatal course, including oral glucose tolerance tests, blood pressure readings, and reviewing previously documented history to identify women at risk with the use of tool designed to correlate this information. This is important as timely referral has been a key component in reducing maternal and neonatal morbidity.1 Treatment of hypertensive disorders once diagnosed remains outside the midwives scope of practice,5 but as elevated BP is often the first clinical indicator of PE, midwives are obligated to refer the woman for further investigations and treatment according to guidelines set by medical organisations such as SOMANZ2 and Australian College of Midwives.5

Discussion 

This literature review aimed to identify predictors of hypertension in pregnancy that could be used by midwives in their scope of practice. The important role of obtaining an accurate medical, family and obstetric history is predominately that of the booking midwife. There are number of factors that can be assessed at this time that have shown to reflect the women's predisposition to development of PE. Physical baseline characteristics such as BMI, age and blood pressure measurement need to be documented accurately.

These assessments can be complemented by information relating to paternity, and ethnicity. Family history has been reinforced as a risk factor, indicating the need to ask comprehensive questions regarding mothers and sisters history relating to PE which can alert the midwife to possible association to developing PE. The initial history appointment needs to be completed both comprehensively and thoroughly, so all relevant information is gathered and assessed, allowing the care giver to formulate an individual care pathway.

Advice given to clients by midwives regarding health and well-being has always been a necessary part of antenatal care. The studies that have been reviewed here did not identify any singular factor that would decrease the risk of PE, however regular exercise, a healthy diet rich in calcium and omega 3 may not only be helpful for prevention of PE, but overall good health for mother and baby and therefore could be safely recommended by midwives.

The need for early referral to medical staff from midwifery-based care of complicated pregnancies to help decrease the long term detrimental effects of hypertension in pregnancy has been well documented and midwives need to be vigilant during their client's antenatal course. Midwives within their scope of practice have the opportunity to both identify and predict PE and are in a position to identify risk factors and thereby provide the best possible care for their mothers and babies.

Conclusion 

Hypertension in pregnancy is a condition that concerns all maternity care providers. Midwives are in the unique position of gathering data from the initial presentation of the women for antenatal care and continuing through the antenatal course. This review found 33 papers that specifically addressed prevention, screening and prediction of PE within the scope of practice of the midwife. Reviewing research relating to modifiable factors, non-modifiable factors and clinical assessment provides a useful framework for gathering information that could predict PE such as family history, parity, previous pregnancy details and highlights the importance of accurate and timely assessment of BP, BMI, OGTT and fetal assessment which may prove vital for the early prediction of PE. This review focused on healthy low-risk women, women who would not automatically be referred for early testing or monitoring, but could screened for hypertension in pregnancy by midwives. Further research should focused on the factors assessed by midwives during history taking and the antenatal period and whether or not these can be synthesised in to a hypertension-specific diagnostic tool for use by midwives in practice.