Chronic Hypertension Increases Risk for Pregnancy Problems

Jennifer Garcia

April 16, 2014

The risk for preeclampsia is 7.7 times greater for women with chronic hypertension compared with the general pregnancy population, and women with chronic hypertension are more likely to experience adverse neonatal outcomes, according to results of a new systematic literature review and meta-analysis spanning 25 countries. These results were published online April 15 in BMJ.

Kate Bramham, MD, from the Division of Women's Health, King's College London, United Kingdom, and colleagues reviewed 55 eligible studies of pregnant women with chronic hypertension published through June 2013, including 795,221 pregnancies and 812,772 infants. The researchers excluded studies that excluded women with superimposed preeclampsia and those that categorized women with preeclampsia and chronic hypertension together with low-risk women with preeclampsia. They compared data from the included studies with data from US cohorts with general population incidence rates obtained from the 2006 US National Vital Statistics Report.

Among the US population, the researchers found that women with chronic hypertension had an increased relative risk (RR) for superimposed preeclampsia compared with preeclampsia (RR, 7.7; 95% confidence interval [CI], 5.7 - 10.1), caesarean section (RR, 1.3; 95% CI, 1.1 - 1.5), preterm delivery at less than 37 weeks' gestation (RR, 2.7; 95% CI, 1.9 - 3.6), birth weight lower than 2500 g (RR, 2.7; 95% CI, 1.9 - 3.8), neonatal unit admission (RR, 3.2; 95% CI, 2.2 - 4.4), and perinatal death (RR, 4.2; 95% CI, 2.7 - 6.5) when compared with the general population of pregnant women. Additional meta-regression did not identify any influential demographic factors.

The researchers note that overall, women with chronic hypertension had a greater pooled incidence of superimposed preeclampsia (25.9%; 95% CI, 21.0% - 31.5%), caesarean section (41.4%; 95% CI, 35.5% - 47.7%), preterm delivery at less than 37 weeks' gestation (28.1%; 95% CI, 22.6% - 34.4%), birth weight of less than 2500 g (16.9%; 95% CI, 13.1% - 21.5%), neonatal unit admission (20.5%; 95% CI, 15.7% - 26.4%), and perinatal death (4.0%; 95% CI, 2.9% - 5.4%).

"To our knowledge, few other detailed meta-analyses of outcomes of pregnancy in women with chronic hypertension have been reported," the study authors write.

"This meta-analysis of outcomes can be used before pregnancy and antenatally by healthcare professionals (including those not providing direct maternity care) advising women with chronic hypertension regarding possible adverse pregnancy events," the study authors write.

They add that "[h]eterogeneity between studies existed, and 95% prediction intervals were broad," which may indicate variability among chronic hypertension populations overall or that determination of chronic hypertension and outcomes is inconsistent. Further exploration of differences such as maternal age, economic wealth of country, parity, study design, and definition of hypertension did not yield any systematic differences in event rates that would explain the heterogeneity.

In an accompanying editorial, Tine D. Clausen, MD, and Thomas Bergholt, MD, PhD, from the Nordsjællands Hospital, University of Copenhagen, Denmark, write: "The high prevalence and relative risk of superimposed pre-eclampsia is particular[ly] concerning, as the condition is associated with an increased risk of serious or potentially life threatening complications for both mother and child."

The editorialists point out that although the data provided by Dr. Bramham and colleagues "adds important knowledge on a scale that has not previously been published," there is still little known about how to prevent adverse outcomes related to chronic hypertension during pregnancy.

"An urgent need remains for research to establish best clinical practice for antenatal care, antihypertensive treatment, and timing of labor in women with uncomplicated chronic hypertension during pregnancy," conclude Dr. Clausen and Dr. Bergholt.

Funding for this study was provided by a doctoral research training fellowship issued by the National Institute for Health Research. The authors and editorialists have disclosed no relevant financial relationships.

BMJ. Published online April 15, 2014. Full text

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