Chronic hypertension weakens tie between prepregnancy BMI and stillbirth, perinatal death

Key takeaways:

• At 26 to 35 weeks’ gestation, women with chronic hypertension had lower stillbirth and perinatal death risks despite high BMI.
• At full term, this link was similar for women with vs. without chronic hypertension.

Women with high prepregnancy BMI have higher stillbirth and perinatal death risks, but this association weakens with chronic hypertension presence, becoming similar or reversing at 26 to 35 weeks’ gestation, researchers reported.

“Prior studies have shown an overall increase in the risk of stillbirth and perinatal death in women with various chronic conditions; however, less evidence is available about gestational age-specific risk of adverse birth outcomes among overweight and obese women with concurrent comorbidity, which is increasingly common,” Jeffrey N. Bone, MSc, biostatistical lead in the clinical research support unit at British Columbia Children’s Hospital Research Institute, the department of obstetrics and gynecology at the University of British Columbia and the Children’s and Women’s Hospital and Health Centre of British Columbia, and colleagues wrote. “Such information could help to create specific guidelines for obstetric intervention in these women.”

Bone and colleagues conducted a retrospective, population-based study, published in the American Journal of Obstetrics and Gynecology, using data from 7,365,797 singleton births in the U.S. from 2016 to 2017 from live birth and fetal death certificates from the National Center for Health Statistics. Researchers evaluated the gestational age-specific relationship between prepregnancy BMI and stillbirth and perinatal death in women with and without chronic hypertension.

Overall, 3.5% of women were underweight, 43.9% had normal weight, 26.1% had overweight, 14.5% had obesity class I, 7% had obesity class II and 5% had obesity class III.

Stillbirth rates rose with rising BMI and remained higher for women with vs. without chronic hypertension (14.2 vs. 4.7 per 1,000 total births).

Cumulative stillbirth incidence increased for each gestational week and increased by BMI category for women without chronic hypertension. However, for women with chronic hypertension, increased stillbirth risk with higher BMI reversed at 26 to 35 weeks’ gestation. At full-term gestation, stillbirth differences between women with and without chronic hypertension were no longer observed.

Researchers observed similar results when evaluating prepregnancy BMI and perinatal death risk.

“Our results suggest that, in obese women, optimal timing of delivery may differ depending on the presence of chronic hypertension,” the researchers wrote.