Prehypertension in late pregnancy was associated with increased risks of small-for-gestational-age (SGA) birth or stillbirth, according to research published in Hypertension.
Researchers hypothesized that prehypertension in late pregnancy would have increased risks of adverse fetal outcomes—including SGA birth and stillbirth—varied by blood pressure changes. They also examined blood pressure changes in early and late pregnancy. Prehypertension is defined as diastolic blood pressure (DBP) between 80 and 89 mm Hg or systolic blood pressure (SBP) between 120 and 139 mm Hg.
Of the 16 864 women they evaluated, 11.2% had prehypertension at 36 gestational weeks. SGA birth risk increased by 2.5% (95% confidence interval [CI]: 1.8-3.0) per mm Hg in DBP at 36 weeks, but stillbirth risk did not significantly increase (1.5%; 95% CI: -0.5 to 3.6). Women with prehypertension had a 70% increased risk of both SGA birth and stillbirth compared with normotensive women (DBP <80 mm Hg) at 36 weeks.
Covariates included maternal age at delivery, maternal height, early pregnancy BMI, presence of pregestational or gestational diabetes, living with a partner, and smoking habits in early pregnancy. Prehypertension was more common in primiparous women, in women who lived with their partners, and in women with diabetes. Interestingly, maternal age and smoking did not appear to influence prehypertension risk.
As the authors explained, women undergo physiological changes during pregnancy as plasma volume and cardiac output increases and total peripheral resistance decreases. Maternal blood pressure levels may rise due to reduced uteroplacental perfusion, via an increased production of vasoconstrictive agents.
“We speculate that differences in efficiency of maternal cardiovascular adaptation might explain why some women with fetal growth restriction (and reduced uteroplacental perfusion) increase their blood pressure beyond the threshold of pregnancy hypertensive disorder, whereas others do not.”
Despite SGA birth risk, researchers “do not suggest blood pressure medication in these women because earlier studies have failed to show improved fetal outcome when lowering blood pressures below a prehypertensive level.”
“The greatest impact of our findings,” they concluded, “is probably the improved insight to the relationship between maternal blood pressure, placental function, and fetal well-being.”
Wikström A-K, Gunnarsdottir J, Nelander M, Simic M, Stephansson O, Cnattinguius S. Prehypertension in pregnancy and risks of small gestational age infant and stillbirth. Hypertension. 2016;67. doi: 10.1161/HYPERTENSIONAHA.115.06752.