Rising classes of obesity are linked with progressively increased risk of early-onset hypertensive disorders in pregnant women, as has been established for late-onset hypertensive disorders, according to a U.S.-based retrospective cohort study.
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Between 4% and 8% of pregnancies are impacted by hypertensive disorders, and preeclampsia is associated with a doubling of adverse neonatal events and causes 16% of maternal deaths in developed countries, previous studies have found. This study showed a clear risk of early-onset hypertensive disorders (less than 34 weeks’ gestation), which may be more deadly than late-onset disease: Compared with later-developing disorders, early hypertensive disorders are linked to a 400% increased risk of perinatal death and a 100%-300% increased risk of severe cardiovascular, renal, or hepatic maternal morbidity, according to previous studies.
The new research, led by Matthew Bicocca, MD, of the University of Texas Health Science Center, Houston, was published in Obstetrics & Gynecology. The researchers analyzed data from U.S. Vital Statistics, including over 14 million singleton births. The sample excluded women with chronic hypertension and a body mass index (BMI) below 18.5 kg/m2.
Previous studies demonstrated that obesity is a risk factor for late-onset hypertensive disorders, but studies of early-onset hypertensive disorders have yielded conflicting results. That could be because early-onset disorders are rare, representing just 5%-10% of hypertensive disorders during pregnancy, making it difficult to obtain a sufficient sample size to show a relationship.
“We know that obese pregnant women are at increased risk for adverse pregnancy outcomes, and this is of particular importance with the increasing prevalence of obesity in the United States. As this is a nationwide cohort with a large sample size, it allowed for evaluation of the rare outcome of early-onset hypertensive disorders of pregnancy,” said Iris Krishna, MD, MPH, an assistant professor of maternal-fetal medicine at Emory University, Atlanta, who was asked to comment on the study.
The researchers classified the women in the study as nonobese (BMI, 18.5-29.9 kg/m2; 46%), class I obese (BMI, 30.0-34.9; 29%), class II obese (BMI, 35.0-39.9; 15%), or class III obese (BMI, 40 or higher; 10%). About 6% of the participants developed hypertensive disorders during pregnancy (0.3% early onset), and the associated risk was greater with increasing class of obesity. Compared with nonobese women, class III obesity was associated with the highest adjusted risk ratio (2.18; 95% confidence interval, 2.12-2.24) for early-onset hypertensive disorders, followed by class II obesity (aRR, 1.57; 95% CI, 1.53-1.62) and class I (aRR, 1.13; 95% CI, 1.10-1.16). A similar pattern was observed with late-onset hypertensive disorders, with the highest risk associated with class III obese (aRR, 3.93; 95% CI, 3.91-3.96), followed by class II (aRR, 2.60; 95% CI, 2.58-2.62) and class I (aRR, 1.71; 95% CI, 1.70-1.73).
The mechanism underlying any potential link between obesity and risk of hypertensive orders of pregnancy isn’t completely understood, especially because the early-onset and late-onset hypertensive disorders have differing pathophysiology. “Early onset is the result from abnormal placentation [leading to] chronic placental insufficiency, and late onset likely [results from] placental insufficiency paired with oxidative stress from conditions such as obesity and insulin resistance,” Dr. Krishna said.
The new research reinforces the need for obese women to receive early prenatal care and counseling on nutrition and exercise “to mitigate weight gain during pregnancy in hopes of reducing their risk for adverse pregnancy outcomes, such as hypertensive disorders of pregnancy,” she concluded.
No source of funding was disclosed. The authors reported having no potential conflicts of interest.
SOURCE: Bicocca M et al. Obstet Gynecol. 2020 Jun 11. doi: 10.1097/AOG.0000000000003901.