In a study published recently in the journal O&G Open, researchers found 39 weeks of gestation is optimal for delivery when chronic hypertension is a factor.

Current recommendations advocate for delivery between 37 and 39 weeks, but those guidelines are based on limited evidence. This first-of-its-kind study used a national, contemporary patient data set to show why 39 weeks is optimal.

Researchers used U.S. Centers for Disease Control and Prevention birth records from 2014 to 2018, which included about 227,000 women, making it the largest study to date to look at delivery timing in pregnant moms with chronic hypertension.

“This study has widespread relevance because it used a large-scale data set that encompassed all births in the U.S. in the given time frame to provide data-driven recommendations for delivery timing among women with chronic hypertension,” said corresponding author Robert Rossi, MD, associate professor in the Department of Obstetrics and Gynecology and director of the Division of Maternal-Fetal Medicine, a subspecialty that focuses on managing high-risk pregnancies.

Data shows 3% to 10% of pregnant women have hypertension, a vascular disorder that affects blood flow to the uterus and placenta and can impact the growth of a fetus. Chronic hypertension can lead to preeclampsia, preterm birth, stillbirth, low birth weight and newborn death after delivery.

Rossi said their study offers evidence that women with chronic hypertension should not stay pregnant past 39 weeks of gestation — but may also benefit from avoiding an early-term birth, defined as before 39 weeks, unless other adverse conditions are present.

The research concluded that among patients with chronic hypertension, delivery at 39 weeks provides the optimal balance between the risk of stillbirth associated with ongoing pregnancy and the risks of infant health issues or death associated with a birth before 39 weeks.

The research team also found the same optimal delivery timing in African American women, who are disproportionately impacted by chronic hypertension during pregnancy and are at higher risk for stillbirth and infant death.

“For every roughly 100 patients with chronic hypertension who deliver at 39 weeks instead of 40 weeks, we would expect to see one less stillbirth, infant death or adverse newborn outcome,” said Rossi.

Optimal delivery timing is essential, he explained, because the prevalence of chronic hypertension during pregnancy is increasing.

“In the future, it will also be important to study patients who are medicated for their chronic hypertension during pregnancy to see if they should also deliver at 39 weeks, or if earlier delivery is more beneficial to this specific group,” said Rossi.

Rossi’s study collaborators included primary author Ira Hamilton, MD, a former UC College of Medicine maternal-fetal medicine fellow who now practices in the Toledo area; Emily DeFranco, DO, former director of the UC Division of Maternal-Fetal Medicine who now is chair of obstetrics and gynecology at the University of Kentucky College of Medicine; James Liu, MD, another former UC maternal-fetal medicine fellow who now practices in Colorado; and Labeena Wajahat, MD; a former UC obstetrics and gynecology resident who now practices in Texas.