The detection, investigation and management of hypertension in pregnancy: full consensus statement

Accuracy of mean arterial pressure and blood pressure measurements in predicting pre-eclampsia: systematic review and meta-analysis

OBJECTIVE

To determine the accuracy of using systolic and diastolic blood pressure, mean arterial pressure, and increase of blood pressure to predict pre-eclampsia.

DESIGN

Systematic review with meta-analysis of data on test accuracy.

DATA SOURCES

Medline, Embase, Cochrane Library, Medion, checking reference lists of included articles and reviews, contact with authors. Review methods Without language restrictions, two reviewers independently selected the articles in which the accuracy of blood pressure measurement during pregnancy was evaluated to predict pre-eclampsia. Data were extracted on study characteristics, quality, and results to construct 2x2 tables. Summary receiver operating characteristic curves and likelihood ratios were generated for the various levels and their thresholds.

RESULTS

34 studies, testing 60 599 women (3341 cases of pre-eclampsia), were included. In women at low risk for pre-eclampsia, the areas under the summary receiver operating characteristic curves for blood pressure measurement in the second trimester were 0.68 (95% confidence interval 0.64 to 0.72) for systolic blood pressure, 0.66 (0.59 to 0.72) for diastolic blood pressure, and 0.76 (0.70 to 0.82) for mean arterial pressure. Findings for the first trimester showed a similar pattern. Second trimester mean arterial pressure of 90 mm Hg or more showed a positive likelihood ratio of 3.5 (95% confidence interval 2.0 to 5.0) and a negative likelihood ratio of 0.46 (0.16 to 0.75). In women deemed to be at high risk, a diastolic blood pressure of 75 mm Hg or more at 13 to 20 weeks' gestation best predicted pre-eclampsia: positive likelihood ratio 2.8 (1.8 to 3.6), negative likelihood ratio 0.39 (0.18 to 0.71). Additional subgroup analyses did not show improved predictive accuracy.

CONCLUSION

When blood pressure is measured in the first or second trimester of pregnancy, the mean arterial pressure is a better predictor for pre-eclampsia than systolic blood pressure, diastolic blood pressure, or an increase of blood pressure.

Metformin versus insulin for the treatment of gestational diabetes

BACKGROUND

Metformin is a logical treatment for women with gestational diabetes mellitus, but randomized trials to assess the efficacy and safety of its use for this condition are lacking.

METHODS

We randomly assigned 751 women with gestational diabetes mellitus at 20 to 33 weeks of gestation to open treatment with metformin (with supplemental insulin if required) or insulin. The primary outcome was a composite of neonatal hypoglycemia, respiratory distress, need for phototherapy, birth trauma, 5-minute Apgar score less than 7, or prematurity. The trial was designed to rule out a 33% increase (from 30% to 40%) in this composite outcome in infants of women treated with metformin as compared with those treated with insulin. Secondary outcomes included neonatal anthropometric measurements, maternal glycemic control, maternal hypertensive complications, postpartum glucose tolerance, and acceptability of treatment.

RESULTS

Of the 363 women assigned to metformin, 92.6% continued to receive metformin until delivery and 46.3% received supplemental insulin. The rate of the primary composite outcome was 32.0% in the group assigned to metformin and 32.2% in the insulin group (relative risk, 0.99 [corrected]; 95% confidence interval, 0.80 [corrected] to 1.23 [corrected]). More women in the metformin group than in the insulin group stated that they would choose to receive their assigned treatment again (76.6% vs. 27.2%, P<0.001). The rates of other secondary outcomes did not differ significantly between the groups. There were no serious adverse events associated with the use of metformin.

CONCLUSIONS

In women with gestational diabetes mellitus, metformin (alone or with supplemental insulin) is not associated with increased perinatal complications as compared with insulin. The women preferred metformin to insulin treatment. (Australian New Zealand Clinical Trials Registry number, 12605000311651.).

Use of uterine artery Doppler ultrasonography to predict pre-eclampsia and intrauterine growth restriction: a systematic review and bivariable meta-analysis

BACKGROUND

Alterations in waveforms in the uterine artery are associated with the development of pre-eclampsia and intrauterine growth restriction. We investigated the predictive accuracy of all uterine artery Doppler indices for both conditions in the first and second trimesters.

METHODS

We identified relevant studies through searches of MEDLINE, EMBASE, the Cochrane Library and Medion databases (all records to April 2006) and by checking bibliographies of identified studies and consulting with experts. Four of us independently selected studies, extracted data and assessed study validity. We performed a bivariable meta-analysis of sensitivity and specificity and calculated likelihood ratios.

RESULTS

We identified 74 studies of pre-eclampsia (total 79,547 patients) and 61 studies of intrauterine growth restriction (total 41 131 patients). Uterine artery Doppler ultrasonography provided a more accurate prediction when performed in the second trimester than in the first-trimester. Most Doppler indices had poor predictive characteristics, but this varied with patient risk and outcome severity. An increased pulsatility index with notching was the best predictor of pre-eclampsia (positive likelihood ratio 21.0 among high-risk patients and 7.5 among low-risk patients). It was also the best predictor of overall (positive likelihood ratio 9.1) and severe (positive likelihood ratio 14.6) intrauterine growth restriction among low-risk patients.

INTERPRETATION

Abnormal uterine artery waveforms are a better predictor of pre-eclampsia than of intrauterine growth restriction. A pulsatility index, alone or combined with notching, is the most predictive Doppler index. These indices should be used in clinical practice. Future research should also concentrate on combining uterine artery Doppler ultrasonography with other tests.

Pregnancy-induced hypertension and the neonatal outcome

OBJECTIVES:This cross-sectional study were to identify the prevalence of pregnancy-induced hypertension and to verify diastolic blood pressure (DBP) association with type of birth and perinatal outcome. METHODS: The data were collected from the mothers' records, in the governmental maternity hospital indicated for high-risk pregnancies, in São Paulo city. RESULTS: During hospitalization, 62.1% had systolic blood pressure > 160 mmHg and 49.6% had a DBP < 110 mmHg. There was no significant association of DBP (p=0.799). The frequency of caesarean section was 64.5%, 28.9% for normal birth, and 6.6% for forceps; 93.4% were live born, 81.0% weighed > 2,500 g, 10.6% were premature, 68.1% were born with adequate gestational age, 84.0% and 99.2% had APGAR score > 7 at 1st and 5th minutes, respectively. CONCLUSION: The DBP e" 110 mmHg was associated with low birth weight (p=0.002) and prematurity (p=0.013).

The accuracy of reporting of the hypertensive disorders of pregnancy in population health data

OBJECTIVE

To assess the accuracy of hypertensive disorders of pregnancy reporting in birth and hospital discharge data compared with data abstracted from medical records.

METHODS

Data from a validation study of 1200 women provided the 'gold standard' for hypertension status. The validation data were linked to both hospital discharge and birth databases. Hypertension could be reported in one, both, or neither database.

RESULTS

Of the 1184 records available for review, 8.3% of women had pregnancy-related hypertension and 1.3% had chronic hypertension. Reporting sensitivities ranged from 23% to 99% and specificities from 96% to 100%. Using broad rather than specific categories of hypertension and more than one source to identify hypertension improved case ascertainment. Women with severe preeclampsia or adverse outcomes were more likely to have their pregnancy-related hypertension reported. When the hypertension reporting was discordant on the birth and hospital discharge data, the hospital data were more accurate.

CONCLUSIONS

Pregnancy-related hypertension is reported with a reasonable level of accuracy, but chronic hypertension is markedly under-ascertained, even when cases were identified from more than one source. Milder forms of hypertension are more likely to go unreported. Studies utilizing population health data may overestimate the proportion of more severe forms of disease and any risk these conditions contribute to other outcomes.

[Current recommendations for the treatment of preeclampsia]

Low-dose aspirin, but not vitamin C and vitamin E, has small to moderate benefits when used for the prevention of preeclampsia. There is however little to suggest that the course of manifest preeclampsia can be substantially affected by drug treatment. Antihypertensive therapy increases the risk of fetal growth restriction and is only indicated in severe hypertension to reduce the risk of maternal cerebral hemorrhage. Magnesium sulfate is the drug of choice for the prevention and treatment of eclampsia. Volume expansion as well as the use of steroids in preeclamptic patients without HELLP syndrome have failed to show any improvement. Delivery as the only definitive treatment is always beneficial for the mother whereas expectant management is in favor of a premature fetus. Decision-making largely depends on gestational age and severity of the disease.

Systematic review: Accuracy of body mass index in predicting pre-eclampsia: bivariate meta-analysis

OBJECTIVE

The objective of this study was to determine the accuracy of body mass index (BMI) (pre-pregnancy or at booking) in predicting pre-eclampsia and to explore its potential for clinical application.

DESIGN

Systematic review and bivariate meta-analysis.

SETTING

Medline, Embase, Cochrane Library, MEDION, manual searching of reference lists of review articles and eligible primary articles, and contact with experts.

POPULATION

Pregnant women at any level of risk in any healthcare setting.

METHODS

Reviewers independently selected studies and extracted data on study characteristics, quality, and accuracy. No language restrictions.

MAIN OUTCOME MEASURES

Pooled sensitivities and specificities (95% CI), a summary receiver operating characteristic curve, and corresponding likelihood ratios (LRs). The potential value of BMI was assessed by combining its predictive capacity for different prevalences of pre-eclampsia and the therapeutic effectiveness (relative risk 0.90) of aspirin.

RESULTS

A total of 36 studies, testing 1,699,073 pregnant women (60,584 women with pre-eclampsia), met the selection criteria. The median incidence of pre-eclampsia was 3.9% (interquartile range 1.4-6.8). The area under the curve was 0.64 with 93% of heterogeneity explained by threshold differences. Pooled estimates (95% CI) for all studies with a BMI > or = 25 were 47% (33-61) for sensitivity and 73% (64-83) for specificity; and 21% (12-31) and 92% (89-95) for a BMI > or = 35. Corresponding LRs (95% CI) were 1.7 (0.3-11.9) for BMI > or = 25 and 0.73 (0.22-2.45) for BMI < 25, and 2.7 (1.0-7.3) for BMI > or = 35 and 0.86 (0.68-1.07) for BMI < 35. The number needed to treat with aspirin to prevent one case of pre-eclampsia ranges from 714 (no testing, low-risk women) to 37 (BMI > or = 35, high-risk women).

CONCLUSIONS

BMI appears to be a fairly weak predictor for pre-eclampsia. Although BMI is virtually free of cost, noninvasive, and ubiquitously available, its usefulness as a stand-alone test for risk stratification must await formal cost-utility analysis. The findings of this review may serve as input for such analyses.

Birth after caesarean study--planned vaginal birth or planned elective repeat caesarean for women at term with a single previous caesarean birth: protocol for a patient preference study and randomised trial

BACKGROUND

For women who have a caesarean section in their preceding pregnancy, two care policies for birth are considered standard: planned vaginal birth and planned elective repeat caesarean. Currently available information about the benefits and harms of both forms of care are derived from retrospective and prospective cohort studies. There have been no randomised trials, and recognising the deficiencies in the literature, there have been calls for methodologically rigorous studies to assess maternal and infant health outcomes associated with both care policies. The aims of our study are to assess in women with a previous caesarean birth, who are eligible in the subsequent pregnancy for a vaginal birth, whether a policy of planned vaginal birth after caesarean compared with a policy of planned repeat caesarean affects the risk of serious complications for the woman and her infant.

METHODS/DESIGN

DESIGN

Multicentered patient preference study and a randomised clinical trial.

INCLUSION CRITERIA

Women with a single prior caesarean presenting in their next pregnancy with a single, live fetus in cephalic presentation, who have reached 37 weeks gestation, and who do not have a contraindication to a planned VBAC. Trial Entry & Randomisation: Eligible women will be given an information sheet during pregnancy, and will be recruited to the study from 37 weeks gestation after an obstetrician has confirmed eligibility for a planned vaginal birth. Written informed consent will be obtained. Women who consent to the patient preference study will be allocated their preference for either planned VBAC or planned, elective repeat caesarean. Women who consent to the randomised trial will be randomly allocated to either the planned vaginal birth after caesarean or planned elective repeat caesarean group. Treatment Groups: Women in the planned vaginal birth group will await spontaneous onset of labour whilst appropriate. Women in the elective repeat caesarean group will have this scheduled for between 38 and 40 weeks. Primary Study Outcome: Serious adverse infant outcome (death or serious morbidity).

SAMPLE SIZE

2314 women in the patient preference study to show a difference in adverse neonatal outcome from 1.6% to 3.6% (p = 0.05, 80% power).

Instituting Surveillance Guidelines and Adverse Outcomes in Preeclampsia

OBJECTIVE

To assess the incidence of combined adverse maternal and perinatal outcomes in women with preeclampsia before and after introducing standardized assessment and surveillance.

METHODS

This study was a preintervention (retrospective) compared with a postintervention (prospective) cohort comparison in a single-tertiary, perinatal unit that included women admitted to hospital with preeclampsia. We interrogated an existing retrospective 24-month database and then introduced the guidelines, assessing the incidence of the combined adverse maternal and perinatal outcomes for 41 months (September 2003 through February 2007). Tests of organ (dys)function were performed at least as often as on the day of admission, admission day +1, every Monday and Thursday, day of delivery, and delivery day +1. All data were checked for errors. The combined maternal outcome was maternal death or one or more of hepatic failure, hematoma, or rupture, Glasgow coma score of less than 13, stroke, at least two seizures, cortical blindness, need for positive inotrope support, myocardial infarction, infusion of any third antihypertensive, renal dialysis, renal transplantation, at least 50% FIO(2) for greater than 1 hour, intubation, or transfusion of at least 10 units of blood products. The combined perinatal outcome was perinatal or infant mortality, bronchopulmonary dysplasia, necrotizing enterocolitis, grade III/IV intraventricular hemorrhage, cystic periventricular leukomalacia, or stage 3-5 retinopathy of prematurity.

RESULTS

Two hundred ninety-five and 405 women were in the preintervention and postintervention cohorts, respectively. The incidence of adverse maternal outcome fell (5.1% to 0.7%; Fisher P<.001; odds ratio 0.14, 95% confidence interval 0.04-0.49). Perinatal outcomes did not change.

CONCLUSION

Standardized surveillance of women with preeclampsia was associated with reduced maternal risk.

Antiplatelet agents for prevention of pre-eclampsia: a meta-analysis of individual patient data

BACKGROUND

Pre-eclampsia is a major cause of mortality and morbidity during pregnancy and childbirth. Antiplatelet agents, especially low-dose aspirin, might prevent or delay pre-eclampsia, and thereby improve outcome. Our aim was to assess the use of antiplatelet agents for the primary prevention of pre-eclampsia, and to explore which women are likely to benefit most.

METHODS

We did a meta-analysis of individual patient data from 32,217 women, and their 32,819 babies, recruited to 31 randomised trials of pre-eclampsia primary prevention.

FINDINGS

For women assigned to receive antiplatelet agents rather than control, the relative risk of developing pre-eclampsia was 0.90 (95% CI 0.84-0.97), of delivering before 34 weeks was 0.90 (0.83-0.98), and of having a pregnancy with a serious adverse outcome was 0.90 (0.85-0.96). Antiplatelet agents had no significant effect on the risk of death of the fetus or baby, having a small for gestational age infant, or bleeding events for either the women or their babies. No particular subgroup of women was substantially more or less likely to benefit from antiplatelet agents than any other.

INTERPRETATION

Antiplatelet agents during pregnancy are associated with moderate but consistent reductions in the relative risk of pre-eclampsia, of birth before 34 weeks' gestation, and of having a pregnancy with a serious adverse outcome.

Medications during pregnancy: antihypertensives and immunosuppressives

Use of prescription and nonprescription medications is common during pregnancy and is required in many women with underlying kidney disease or hypertension and in all with solid-organ allografts. Systematic assessment of drug safety during pregnancy is lacking, as are rigorous and comprehensive studies of pharmacokinetics and pharmacodynamics to guide drug selection and dosing across pregnancy. Renal and hepatic clearances of many drugs change markedly during pregnancy and pitfalls may complicate routine therapeutic monitoring of some drugs during pregnancy. However, available data and clinical experience allow reasonable strategies for selection and dosing of immunosuppressive agents in pregnant transplant recipients and of antihypertensive agents in women with mild or more severe hypertension complicating their pregnancies.

Hypertension in pregnancy

Hypertensive disorders of pregnancy are the most common medical disorders of pregnancy and are associated with increased maternal and perinatal risks. The pathophysiology, diagnosis, and treatment are herein reviewed for chronic hypertension, preeclampsia, gestational hypertension, and severe hypertension. The benefits and risks of treating mild, moderate, and severe hypertension are discussed. A variety of oral and parenteral therapies are approved for the treatment of hypertension in pregnancy; methyldopa, labetalol, and nifedipine have been used safely in pregnancy, as has hydrochlorothiazide in those already taking this medication before conception. Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers are contraindicated in pregnancy because of adverse fetal effects, and atenolol should be avoided due to concerns with fetal growth. Severe hypertension >160/110 mmHg may require parenteral therapy, and treatment with intravenous labetalol now supplants the use of hydralazine. Women may remain hypertensive for a period postpartum and require treatment for a short interval. Early or severe preeclampsia warrants workup postpartum for secondary causes. Pregnancy induced hypertension or preeclampsia are emerging as risk factors for future cardiovascular risk.

The association between preeclampsia and placental trisomy 16 mosaicism

BACKGROUND

Prenatally diagnosed trisomy 16 mosaicism is associated with the increased risk of poor pregnancy outcome including intrauterine growth restriction, intrauterine death and fetal malformation. While maternal preeclampsia has also been reported in some cases, this has not been systematically evaluated.

METHODS

To better define the risk of preeclampsia and the clinical course of preeclampsia in these pregnancies and to identify associated clinical variables, we reviewed 25 cases of prenatally diagnosed trisomy 16 mosaicism for which molecular studies were undertaken and sufficient obstetrical data were present to include/exclude the diagnosis of preeclampsia.

RESULTS

Six of 25 (24%) mosaic trisomy 16 cases exhibited preeclampsia as compared to 3 of 44 (7%) matched controls. There were no differences between those mosaic trisomy 16 cases presenting with preeclampsia and those that did not, in terms of the presence/absence of UPD, IUGR, malformation, or trisomy on amniocentesis. Four of the 6 (67%) preeclampsia-associated fetuses were male, compared with only 4 of 19 (21%) (p = 0.06) nonpreeclampsia case fetuses, and three of these also had hypospadias. The levels of trisomy tended to be high in placentas associated with preeclampsia; however very high levels of placental trisomy were also often seen in the absence of preeclampsia.

CONCLUSION

As it is impossible to predict which subset of cases is at highest risk, all women receiving a prenatal diagnosis of trisomy 16 mosaicism should be closely monitored for signs of preeclampsia.

Methods for dealing with discrepant records in linked population health datasets: a cross-sectional study

BACKGROUND

Linked population health data are increasingly used in epidemiological studies. If data items are reported on more than one dataset, data linkage can reduce the under-ascertainment associated with many population health datasets. However, this raises the possibility of discrepant case reports from different datasets.

METHODS

We examined the effect of four methods of classifying discrepant reports from different population health datasets on the estimated prevalence of hypertensive disorders of pregnancy and on the adjusted odds ratios (aOR) for known risk factors. Data were obtained from linked, validated, birth and hospital data for women who gave birth in a New South Wales hospital (Australia) 2000-2002.

RESULTS

Among 250,173 women with linked data, 238,412 (95.3%) women had perfect agreement on the occurrence of hypertension, 1577 (0.6%) had imperfect agreement; 9369 (3.7%) had hypertension reported in only one dataset (under-reporting) and 815 (0.3%) had conflicting types of hypertension. Using only perfect agreement between birth and discharge data resulted in the lowest prevalence rates (0.3% chronic, 5.1% pregnancy hypertension), while including all reports resulted in the highest prevalence rates (1.1 % chronic, 8.7% pregnancy hypertension). The higher prevalence rates were generally consistent with international reports. In contrast, perfect agreement gave the highest aOR (95% confidence interval) for known risk factors: risk of chronic hypertension for maternal age > or =40 years was 4.0 (2.9, 5.3) and the risk of pregnancy hypertension for multiple birth was 2.8 (2.5, 3.2).

CONCLUSION

The method chosen for classifying discrepant case reports should vary depending on the study question; all reports should be used as part of calculating the range of prevalence estimates, but perfect matches may be best suited to risk factor analyses. These findings are likely to be applicable to the linkage of any specialised health services datasets to population data that include information on diagnoses or procedures.

Antihypertensive drug therapy for mild to moderate hypertension during pregnancy

BACKGROUND

Mild to moderate hypertension during pregnancy is common. Antihypertensive drugs are often used in the belief that lowering blood pressure will prevent progression to more severe disease, and thereby improve outcome.

OBJECTIVES

To assess the effects of antihypertensive drug treatments for women with mild to moderate hypertension during pregnancy.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (March 2006), the Cochrane Central Register of Controlled Trials (The Cochrane Library 2005, Issue 3), MEDLINE (1966 to November 2005), LILACS (1984 to November 2005) and EMBASE (1974 to November 2005).

SELECTION CRITERIA

All randomised trials evaluating any antihypertensive drug treatment for mild to moderate hypertension during pregnancy defined, whenever possible, as systolic blood pressure 140 to 169 mmHg and diastolic blood pressure 90 to 109 mmHg. Comparisons were of one or more antihypertensive drug(s) with placebo, with no antihypertensive drug, or with another antihypertensive drug, and where treatment was planned to continue for at least seven days.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data.

MAIN RESULTS

Forty-six trials (4282 women) were included. Twenty-eight trials compared an antihypertensive drug with placebo/no antihypertensive drug (3200 women). There is a halving in the risk of developing severe hypertension associated with the use of antihypertensive drug(s) (19 trials, 2409 women; relative risk (RR) 0.50; 95% confidence interval (CI) 0.41 to 0.61; risk difference (RD) -0.10 (-0.12 to -0.07); number needed to treat (NNT) 10 (8 to 13)) but little evidence of a difference in the risk of pre-eclampsia (22 trials, 2702 women; RR 0.97; 95% CI 0.83 to 1.13). Similarly, there is no clear effect on the risk of the baby dying (26 trials, 3081 women; RR 0.73; 95% CI 0.50 to 1.08), preterm birth (14 trials, 1992 women; RR 1.02; 95 % CI 0.89 to 1.16), or small-for-gestational-age babies (19 trials, 2437 women; RR 1.04; 95 % CI 0.84 to 1.27). There were no clear differences in any other outcomes. Nineteen trials (1282 women) compared one antihypertensive drug with another. Beta blockers seem better than methyldopa for reducing the risk of severe hypertension (10 trials, 539 women, RR 0.75 (95 % CI 0.59 to 0.94); RD -0.08 (-0.14 to 0.02); NNT 12 (6 to 275)). There is no clear difference between any of the alternative drugs in the risk of developing proteinuria/pre-eclampsia. Other outcomes were only reported by a small proportion of studies, and there were no clear differences.

AUTHORS' CONCLUSIONS

It remains unclear whether antihypertensive drug therapy for mild to moderate hypertension during pregnancy is worthwhile.

Serum adiponectin levels in normal and hypertensive pregnancy

OBJECTIVE

The aim of this study was to quantify adiponectin levels in women with normal and hypertensive pregnancies to determine whether there is an independent association, while controlling for body fat and insulin sensitivity.

METHODS

A cross-sectional study was conducted in the following categories: 12 normotensive non-pregnant women, 10 normotensive, 12 gestational hypertensive, 13 essential hypertensive, and 12 preeclamptic women. All subjects underwent measurements of body fat by bio-impedance analysis and blood sampling.

RESULTS

Percentage of body fat and insulin resistance were greater in all pregnant groups compared with non-pregnant women. Adiponectin concentrations were significantly lower in women with normal pregnancies (18.6 +/- 1.4 microg/mL, p = 0.02) compared with non-pregnant women (24.0 +/- 1.5 microg/mL). However, adiponectin levels were not significantly different among normal pregnancy, gestational hypertension (19.0 +/- 3.1 microg/mL), essential hypertension (24.0 +/- 3.7 microg/mL) and pre-eclampsia (22.4 +/- 2.5 microg/mL) groups. Adiponectin levels were inversely related to percent body fat and insulin resistance. When adiponectin levels were corrected for percent body fat and insulin resistance, no significant differences were seen among the study groups.

CONCLUSIONS

Adiponectin levels are decreased in normal pregnancy, however this difference disappears when adiponectin levels are corrected for the pregnancy-related increases in body fat and insulin resistance. Adiponectin levels are not altered significantly in states of hypertension in pregnancy compared with normal pregnancy.

Perinatal outcomes and macrosomia in a multi-ethnic population of women with type 2 diabetes

We reviewed pregnancy outcomes of women with type 2 diabetes giving birth over a six-year period, comparing the main ethnic groups. Asian women had significantly smaller babies and lower rates of macrosomia as defined by standard growth charts. Other outcomes were similar between the Asian, European and Polynesian women.

Prediction of pre-eclampsia: a protocol for systematic reviews of test accuracy

BACKGROUND

Pre-eclampsia, a syndrome of hypertension and proteinuria, is a major cause of maternal and perinatal morbidity and mortality. Accurate prediction of pre-eclampsia is important, since high risk women could benefit from intensive monitoring and preventive treatment. However, decision making is currently hampered due to lack of precise and up to date comprehensive evidence summaries on estimates of risk of developing pre-eclampsia.

METHODS/DESIGN

A series of systematic reviews and meta-analyses will be undertaken to determine, among women in early pregnancy, the accuracy of various tests (history, examinations and investigations) for predicting pre-eclampsia. We will search Medline, Embase, Cochrane Library, MEDION, citation lists of review articles and eligible primary articles and will contact experts in the field. Reviewers working independently will select studies, extract data, and assess study validity according to established criteria. Language restrictions will not be applied. Bivariate meta-analysis of sensitivity and specificity will be considered for tests whose studies allow generation of 2 x 2 tables.

DISCUSSION

The results of the test accuracy reviews will be integrated with results of effectiveness reviews of preventive interventions to assess the impact of test-intervention combinations for prevention of pre-eclampsia.

Pregnancy outcome in women presenting with pre-eclampsia at less than 25 weeks gestation

OBJECTIVE

We aimed to (i) assess maternal and perinatal outcomes in pre-eclampsia at < 25(0) weeks; and (ii) determine if any antenatal factors were associated with adverse maternal and perinatal outcomes.

DESIGN

A retrospective study.

SETTING

Tertiary referral hospital, Auckland, New Zealand.

METHODS

Data were extracted from the clinical record and hospital database. The study population involved women admitted with pre-eclampsia at < 25(0) weeks, with a live singleton pregnancy, from 1997 to 2004 and managed expectantly.

OUTCOME MEASURES

Maternal morbidity, perinatal death, neurodevelopmental outcome at 18 months, small for gestational age assessed by population and customised birthweight centiles.

RESULTS

Gestation at admission was the only antenatal variable associated with adverse perinatal outcome. Of 14 women admitted < 23 weeks, no babies survived, but eight (62%) babies of women admitted in the 24th week (24(0)-24(6)) survived. Neurodevelopmental outcome was assessed in eight of nine survivors; two (25%) had moderate and two (25%) had minor disability. All babies in this cohort had birthweights < 5th customised centile. Only one baby (10%) weighing < 500 g survived.

CONCLUSION

Maternal morbidity was high in this expectantly managed cohort. As no babies survived when pre-eclampsia occurred before 23 weeks, induction of labour should be considered. In the 24th week two-thirds of babies survived and 25% had moderate handicap. This information may help clinicians and women in the future to make informed choices about management.

Caring for pregnant and postnatal women in intensive care: what do we know?

Critically ill pregnant and postnatal women admitted to intensive care units (ICUs) require highly specialised care, components of which many critical care nurses are unfamiliar with. There are no specialist critical care obstetric centres in Australia, with critically ill obstetric patients admitted to general ICUs. There are no published guidelines and little research that assist critical care nurses to care for such women. Furthermore, the admission of pregnant or postnatal women to ICUs is likely to increase with emerging childbearing patterns in Australia. It is therefore timely to review what we know about caring for critically ill pregnant and postnatal women. This paper analyses the literature on intensive care utilisation by obstetric patients and provides an overview regarding which pregnant and postpartum women require intensive care. The key areas of providing mechanical ventilation to pregnant women and assessment of fetal wellbeing are explored in detail. The most frequent conditions and their treatment, preeclampsia and obstetric haemorrhage, are also reviewed. The establishment of lactation is also considered as the critical carenurse is commonly involved in supporting the woman's endeavour to breastfeed.

Vitamins C and E and the risks of preeclampsia and perinatal complications

BACKGROUND

Supplementation with antioxidant vitamins has been proposed to reduce the risk of preeclampsia and perinatal complications, but the effects of this intervention are uncertain.

METHODS

We conducted a multicenter, randomized trial of nulliparous women between 14 and 22 weeks of gestation. Women were assigned to daily supplementation with 1000 mg of vitamin C and 400 IU of vitamin E or placebo (microcrystalline cellulose) until delivery. Primary outcomes were the risks of maternal preeclampsia, death or serious outcomes in the infants (on the basis of definitions used by the Australian and New Zealand Neonatal Network), and delivering an infant whose birth weight was below the 10th percentile for gestational age.

RESULTS

Of the 1877 women enrolled in the study, 935 were randomly assigned to the vitamin group and 942 to the placebo group. Baseline characteristics of the two groups were similar. There were no significant differences between the vitamin and placebo groups in the risk of preeclampsia (6.0 percent and 5.0 percent, respectively; relative risk, 1.20; 95 percent confidence interval, 0.82 to 1.75), death or serious outcomes in the infant (9.5 percent and 12.1 percent; relative risk, 0.79; 95 percent confidence interval, 0.61 to 1.02), or having an infant with a birth weight below the 10th percentile for gestational age (8.7 percent and 9.9 percent; relative risk, 0.87; 95 percent confidence interval, 0.66 to 1.16).

CONCLUSIONS

Supplementation with vitamins C and E during pregnancy does not reduce the risk of preeclampsia in nulliparous women, the risk of intrauterine growth restriction, or the risk of death or other serious outcomes in their infants. (Controlledtrials.com number, ISRCTN00416244.).

Chinese herbal medicine for the treatment of pre-eclampsia

BACKGROUND

Pre-eclampsia is a common disorder of pregnancy with uncertain etiology. In Chinese herbal medicines, a number of herbs are used for treating pre-eclampsia. Traditional Chinese medicine considers that, when a woman is pregnant, most of the blood of the mother is directed to the placenta to provide the baby with the required nutrition; other maternal organs may in consequence be vulnerable to damage. These organs include the liver, the spleen, and the kidneys. The general effects of Chinese herbal medicines that can protect these organs may be valuable in pre-eclampsia by encouraging vasodilatation, increasing blood flow, and decreasing platelet aggregation. The use of Chinese herbal medicine is often based on the individual and presence of traditional Chinese medicine symptoms.

OBJECTIVES

To assess the effect of Chinese herbal medicine for treating pre-eclampsia and compare it with that of placebo, no treatment or Western medicine.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Groups Trial Register (31 March 2005), the Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 1, 2005), MEDLINE (1969 to December 2004), EMBASE (1984 to March 2004) and CBM (1978 to February 2005) and we handsearched several main journals published in China.

SELECTION CRITERIA

Randomized controlled trials in which Chinese herbal medicine was used for treating pre-eclampsia.

DATA COLLECTION AND ANALYSIS

One review author assessed trials for inclusion. The trials were also assessed by a second review author if there was any doubt about whether or not to include the trial. Analysis was not performed as there were no trials included in this review.

MAIN RESULTS

No trials were suitable for inclusion in this review.

AUTHORS' CONCLUSIONS

The effect of Chinese herbal medicine for treating pre-eclampsia remains unclear. There are currently no randomized controlled trials to address the efficacy and safety of Chinese herbal medicine for the treatment of pre-eclampsia. Well conducted randomized controlled trials are required.

The relationship between thrombophilic mutations and preeclampsia: a prospective case-control study

BACKGROUND

Preeclampsia and its association with thrombophilia remain controversial, due to inconsistent results in different studies, which include different ethnic groups, selection criteria, and patient numbers. The aim of this study was to determine the relationship between thrombophilia and preeclamptic patients in our region.

METHODS

In a prospective case-control study, we compared 100 consecutive women with preeclampsia and eclampsia (group 1) with 100 normal pregnant women (group 2). All women were tested two months after delivery for mutations of factor V Leiden, methylenetetrahydrofolate reductase (MTHFR), and prothrombin gene mutation as well as for deficiencies of protein C, protein S, and antithrombin III.

RESULTS

A thrombophilic mutation was found in 42 (42%) and 28 (28%) women in group 1 and group 2, respectively (P=0.27, OR 1.5, 95%CI 1.0-2.2). The incidence of Factor V Leiden mutation (heterozygous), prothrombin mutation (heterozygous), prothrombin mutation (homozygous), MTHFR mutation (homozygous) was not statistically significant in group 1 compared with group 2 (P>0.05). Also, deficiencies of protein S, protein C, and antithrombin III were not statistically significant in group 1 compared with group 2 (P>0.05).

CONCLUSION

There was no difference in thrombophilic mutations between preeclamptic patients and normal pregnant women in our region. Therefore, we suggest that preeclamptic patients should not be tested for thrombophilia.

Pregnancy in women with Type 2 diabetes: who takes metformin and what is the outcome?

AIMS

To review pregnancy outcomes in women with Type 2 diabetes (Type 2 DM), comparing women treated with those not treated with metformin.

METHODS

Data were collected by case-note review for all pregnancies in women with Type 2 DM over a 6-year period (1998-2003) at the National Women's Hospital. Two hundred and fourteen pregnancies were included, metformin was taken in 93 pregnancies and continued until delivery in 32; the remaining 121 pregnancies comprised the control group. The principal outcome measures were preeclampsia, perinatal loss and neonatal morbidity.

RESULTS

Baseline characteristics differed between groups: women in the metformin group had greater mean (SD) body mass index [35.5(7.6) vs. 33.5(6.6) kg/m2, P < 0.05], more chronic hypertension (19% vs. 7%, P < 0.05) and higher mean (SD) first trimester glycated haemoglobin (HbA1c) levels [8.3(1.9)% vs. 7.5(1.7)%, P < 0.005]. There was no difference between metformin and control groups, respectively, in the rate of preeclampsia (13% vs. 14%, P = 0.84), perinatal loss (3% vs. 2%, P = 0.65) or neonatal morbidity, including rate of prematurity (23% vs. 22%, P = 0.7), admission to the neonatal unit (40% vs. 48%, P = 0.27), respiratory distress (9% vs. 18%, P = 0.07) and treatment with intravenous dextrose (20% vs. 31%, P = 0.08).

CONCLUSIONS

Pregnant women with Type 2 DM who were treated with metformin had more risk factors for adverse pregnancy outcomes, but no differences in outcomes were seen compared with women not taking metformin. We need randomized trials to address potential benefits of metformin treatment in this population that may be masked by current practice.

Routine investigations might be useful in pre-eclampsia, but not in gestational hypertension

BACKGROUND

Women referred to secondary care with suspected pregnancy-induced hypertension (PIH) are commonly investigated with blood tests and cardiotocography (CTG), regardless of the clinical severity of their condition. Over-investigation might lead to inappropriate intervention.

AIMS

To investigate how often abnormal blood test and CTG results occur in women with pre-eclampsia and gestational hypertension and in women who do not have pregnancy-induced hypertension.

METHODS

Retrospective case note review of 526 consecutive women referred with suspected pregnancy-induced hypertension to a district hospital. The frequency of abnormal test results and the pregnancy outcomes were analysed according to clinical classification.

RESULTS

36% of women referred did not meet the clinical criteria for a diagnosis of pregnancy-induced hypertension. Abnormalities of platelet count and/or liver function were seen in 11% of women with pre-eclampsia and in less than 2% of women with gestational hypertension and in a similar proportion of women who did not have pregnancy-induced hypertension. Gestational hypertension was associated with increased induction and caesarean birth rates, but not with low birthweight or preterm delivery. Progression from gestational hypertension to pre-eclampsia was not predicted by blood test abnormalities. Support for the routine use of antenatal CTG was not found.

CONCLUSIONS

A clinical diagnosis of pregnancy-induced hypertension should be confirmed before blood tests are ordered. The incidence of test abnormalities was only increased in pre-eclampsia and in gestational hypertension before term. CTG might only be of use in selected cases.

Dietary intake of vitamin C and vitamin E and the development of hypertensive disorders of pregnancy

OBJECTIVES

To explore the relationship, if any, between dietary intake of the antioxidant vitamins C and E, and the development of pre-eclampsia and gestational hypertension.

STUDY DESIGN

A prospective cohort study of pregnant women attending the antenatal clinic of the Women's and Children's Hospital in Adelaide, Australia, was carried out between April and July 2001. Women completed a semi-quantitative 116-item food frequency questionnaire (FFQ). Women's medical records were viewed after birth to collect data on pregnancy outcomes. Relationships were explored through cross-tabulations, chi-square analysis, and adjustments were made for potential confounders using binary logistic regression.

RESULTS

A total of 299 women completed the FFQ. Median intake of vitamin C was 188 mg and for vitamin E was 6.74 mg. There was no relationship between the intake of vitamin C and hypertensive disorders of pregnancy. For vitamin E, being in the lowest quartile of intake, was associated with an increased risk of hypertensive disorders (RR 1.75, 95% CI 1.11-2.75, P = 0.02). This relationship was confirmed after adjusting for the confounding factors of maternal age and parity.

CONCLUSIONS

Little support was found for a relationship between dietary intake of vitamin C and the development of hypertensive disorders of pregnancy. Low vitamin E intake was associated with a significant increase in the risk of hypertensive disorders of pregnancy, even after adjustments were made for confounding factors. Further research is required to investigate whether supplementation above dietary intake of antioxidant vitamins influences the risk of hypertensive disorders of pregnancy.

Hypertensive disorders in pregnancy: a population‐based study

OBJECTIVES

To determine population-based rates and outcomes of hypertensive disorders in pregnancy.

DESIGN

Cross-sectional study using linked population databases.

SETTING AND PARTICIPANTS

All women, and their babies, discharged from hospital following birth in New South Wales, between 1 January 2000 and 31 December 2002.

MAIN OUTCOME MEASURES

Rates of hypertensive disorders in pregnancy, maternal and infant morbidity and mortality, and level of hospital care for the birth admission.

RESULTS

250 173 women and their 255 931 infants were included in the study. Overall, 24 517 women (9.8%) had a hypertensive disorder in pregnancy, including 1411 (0.6%) with chronic hypertension, 10 379 (4.2%) with pre-eclampsia, 731 (0.3%) with chronic hypertension with superimposed pre-eclampsia, and 10 864 (4.3%) with gestational hypertension. Women with, and infants exposed to, hypertension were more likely to suffer death or major morbidity than those without hypertension. Infants of mothers with hypertension were more likely to be to born preterm and small for gestational age. Just over half the women with major morbidity or mortality delivered in hospitals with a high level of medical care. In contrast, most infants with major morbidity or mortality were delivered in hospitals with neonatal intensive care units.

CONCLUSIONS

Hypertension is a common complication of pregnancy, and adverse outcomes are increased among hypertensive women and their babies. Clinicians appear to be better at identifying and seeking an appropriate level of care for pregnancies where the infant is at risk of a poor outcome than when the mother is at risk. More specific antenatal indicators of poor maternal outcome would help guide the referral of hypertensive women to higher levels of care.

The Perinatal Antiplatelet Review of International Studies (PARIS) Collaboration Steering Group on behalf of the PARIS Collaboration, The PARIS Collaboration. Antiplatelet agents for prevention of pre-eclampsia and its consequences: a systematic review and individual patient data meta-analysis

BACKGROUND: There is now good evidence that antiplatelet agents (principally low dose aspirin) prevent pre-eclampsia, a leading cause of morbidity and mortality for pregnant women and their babies. A Cochrane Review identified moderate, but clinically important, reductions in the relative risks of pre-eclampsia (19%), preterm birth (7%) and perinatal mortality (16%) in women allocated antiplatelets, rather than placebo or no antiplatelet.Uncertainty remains, however, about whether some women (in terms of risk) benefit more than others, what dose of aspirin is best and when in pregnancy treatment should ideally start. Rather than undertake new trials, the best way to answer these questions is to utilise existing individual patient data from women enrolled in each trial. METHODS/DESIGN: Systematic review with meta-analysis based on individual patient data. This involves the central collection, validation and re-analysis of thoroughly checked data from individual women in all the available randomised trials.The objective is to confirm that antiplatelet agents, given during pregnancy, will reduce the incidence of pre-eclampsia. The review will then determine the size of this effect, and whether antiplatelets delay the onset of pre-eclampsia or its impact on important outcomes for women and their babies. It will also explore whether the effect of antiplatelets differs by womens' risk profile; when commenced during pregnancy; and/or by dose. DISCUSSION: The PARIS (Perinatal Antiplatelet Review of International Studies) Collaboration has been formed to undertake the review. This will be the first individual patient data review in the perinatal field. Final results should be available by 2006-7.

Variations in Early and Intermediate Neonatal Outcomes for Inborn Infants Admitted to a Canadian NICU and Born of Hypertensive Pregnancies

OBJECTIVE

To determine whether neonatal intensive care unit (NICU) outcomes vary by centre for inborn neonates of hypertensive pregnancies and, if so, whether that variation might be related to between-centre variations in obstetric practice.

METHODS

The study comprised a prospective cohort of 13 505 singleton neonates admitted to 17 Canadian NICUs. Adjusting for potential confounders, we used multivariate regression to analyze the relation between centre of delivery and 6 dependent variables: (1) Apgar score < 7 at 5 minutes; (2) Score of Neonatal Acute Physiology-II (SNAP-II) score > or = 10; (3) neonatal death; (4) neonatal death or morbidity (owing to bronchopulmonary dysplasia [BPD], intraventricular hemorrhage [IVH], necrotizing enterocolitis [NEC], persistent ductus arteriosus [PDA], or periventricular leukomalacia [PVL]); (5) BPD alone; and (6) major neonatal morbidity (that is, at least one of IVH, PVL, NEC, or PDA). NICU practices known to influence these outcomes were included in the modelling for neonatal death and neonatal morbidity. In a sensitivity analysis for practice variation, antenatal steroid exposure was both included and excluded in each regression.

RESULTS

For 5 of the 6 dependent variables, we identified between-centre variation that was not explained solely by variation in antenatal corticosteroid use. Adjusted odds ratios varied from 0.11 to 5.6 (the reference centre was the median rate of the adverse outcome).

CONCLUSIONS

In the pregnancy hypertension setting, between-centre variations in practice are associated with variations in neonatal physiology and survival. For infants admitted to NICU, the obstetric management of hypertensive pregnancies appears to have an effect on both short- and medium-term neonatal outcomes, even after correction for NICU management.

The Prediction of Adverse Maternal Outcomes in Preeclampsia

OBJECTIVES

(1) To evaluate whether clinical variables reflecting the multiorgan dysfunctions of preeclampsia can predict adverse maternal outcomes of preeclampsia; (2) to determine the usefulness of the mean platelet volume (MPV):platelet ratio as a novel measure of platelet consumption in predicting the severity of preeclampsia.

METHOD

A retrospective chart review was conducted of cases of preeclampsia seen in 3 tertiary level units from January 2001 to December 2001. Candidate predictors of adverse maternal outcome were gestational age (GA) on admission to hospital, blood pressure, proteinuria, urine output, uric acid, creatinine, aspartate transaminase (AST), lactate dehydrogenase, bilirubin, albumin, fraction of inspired oxygen:oxygen saturation (FIO2:SaO2) ratio, platelet count, MPV, MPV:platelet ratio, fibrinogen, and seizures. The combined adverse maternal outcomes included maternal death; 1 or more of hepatic failure, hematoma, or rupture; Glasgow coma scale <13; stroke; 2 or more seizures; cortical blindness; positive inotrope support; myocardial infarction; infusion of any third antihypertensive; dialysis; renal transplantation; > or =50% FIO2 for >1 hour; intubation; or transfusion of > or =10 units of blood products. Descriptive, univariable, and multivariable analyses were performed, with significance set at P < .05.

RESULTS

Of a total of 594 women with preeclampsia, 60 (10.1%) developed at least 1 element of the combined adverse outcome; 1 of these 60 women died. The most common outcomes were increased oxygen requirements, the use of a third infused antihypertensive, and transfusion >10 units. In women who developed an adverse outcome, GA and fibrinogen were lower, and total leukocyte count, creatinine, and AST were greater. Multivariable logistic regression revealed that admission GA (odds ratio [OR], 0.91), dipstick protein (OR, 1.31), and MPV:platelet ratio (OR, 391.0) independently predicted the outcome.

CONCLUSIONS

Several promising markers were identified: admission GA, dipstick proteinuria, and the MPV:platelet ratio. MPV:platelet ratio also showed promise as a marker of platelet consumption. A prospective study is required to develop a clinical prediction model for preeclampsia.

Clinical, psychosocial, and economic effects of antenatal day care for three medical complications of pregnancy: a randomised controlled trial of 395 women

BACKGROUND

Day care is increasingly being used for complications of pregnancy, but there is little published evidence on its efficacy. We assessed the clinical, psychosocial, and economic effects of day care for three pregnancy complications in a randomised trial of day care versus standard care on an antenatal ward.

METHODS

395 women were randomly assigned day (263) or ward (132) care in a ratio of two to one, stratified for major diagnostic categories (non-proteinuric hypertension, proteinuric hypertension, and preterm premature rupture of membranes). The research hypothesis was that for these disorders, as an alternative to admission, antenatal day care will reduce specified interventions and investigations, result in no differences in clinical outcome, lead to greater satisfaction and psychological wellbeing, and be more cost-effective. Data were collected through case-note review, self-report questionnaires (response rates 81.0% or higher) and via the hospital's financial system. Analysis was by intention to treat.

FINDINGS

All participants were included in the analyses. There were no differences between the groups in antenatal tests or investigations or intrapartum interventions. The total duration of antenatal care episodes was shorter in the day-care group than in the ward group (median 17 [IQR 5-9] vs 57 [35-123] h; p=0.001). Overall stay was also significantly shorter in the day-care group (mean 7.22 [SE 0.31] vs 8.53 [0.44]; p=0.014). The median number of care episodes was three (range one to 14) in the day-care group and two (one to nine) in the ward group (p=0.01). There were no statistically or clinically significant differences in maternal or perinatal outcomes. The day-care group reported greater satisfaction, with no evidence of unintended psychosocial sequelae. There was no significant difference in either average cost per patient or average cost per day of care.

INTERPRETATION

Since clinical outcomes and costs are similar, adoption by maternity services of a policy providing specified women with the choice between admission and day-unit care seems appropriate.

Hepatitis B surface antigen carrier status and its correlation to gestational hypertension

OBJECTIVE

To determine whether chronic hepatitis B surface antigen (HBsAg) carrier status is associated with an increased incidence of gestational hypertension.

METHODS

A retrospective analysis of all deliveries in a regional obstetric unit over a 4-year period using a comprehensive obstetric database.

RESULTS

The data of 13,792 patients were analysed, of which 1340 (9.71%) were chronic HBsAg carriers. Contrary to our hypothesis, the overall incidence of gestational hypertension was significantly lower in the HBsAg positive group (2.01%) as compared to the negative group (3.58%) (P < 0.01, odds ratio (OR) 0.55, 95% confidence interval (CI) 0.37-0.81). When comparing the incidence of severe preeclampsia, the difference remained significant (0.22 and 0.79%, respectively, P < 0.05, OR 0.28, 95% CI 0.08-0.88). There was otherwise no difference in the incidence of other major obstetric complications between the HBsAg positive and negative groups.

CONCLUSION

The findings presented did not support a positive association between HbsAg carrier status and gestational hypertension. The data from the present study, and re-evaluation of similar published data, in fact suggest the contrary observation of a lower than normal incidence of gestational hypertension in HbsAg positive mothers.

Subclassification of preeclampsia

Preeclampsia is a heterogeneous disorder, and as with other diseases (e.g., type I and type II diabetes), progress in the understanding of this disorder would be assisted greatly if subtypes could be characterized. We suggest that a first step would be to subdivide preeclampsia into early-onset disease (< 34 + 0 weeks') and late onset disease (> 34 + 0 weeks').

Emergency management of eclampsia and severe pre-eclampsia

Eclampsia and severe pre-eclampsia are rare, but potentially life-threatening conditions that emergency physicians must be able to diagnose and treat promptly, because initial presentations to the ED are real possibilities. The treatment of the major complications of this disorder, hypertension and seizures, have been the focus of much research. Magnesium sulphate is now the first line agent for acute treatment and prophylaxis of seizures in eclampsia and pre-eclampsia. Severe pre-eclampsia should be treated with magnesium to prevent progression to eclampsia. Severe hypertension requires treatment with an intravenous antihypertensive agent familiar to the clinician. No single antihypertensive has been proven to be better than another, although in Australia, hydralazine is probably the initial intravenous agent of choice. Routine use of invasive haemodynamic monitoring and volume expansion is not recommended and consultation with obstetric colleagues is essential.