Women who developed prehypertension in late pregnancy were more likely to have stillbirths or underweight babies, researchers found.
According to the Centers for Disease Control and Prevention (CDC), almost 1 in 3 adults in the US have prehypertension, which is blood pressure that is higher than normal - but that is not high enough to be classed as hypertension.
A person with a systolic blood pressure (top number) of 120-139 mm/Hg, a diastolic blood pressure (bottom number) of 80-89 mm/Hg, or both, is classed as prehypertensive.
While previous studies have associated hypertension with increased risk of stillbirth, few studies have assessed how prehypertension that develops during pregnancy may impact such risk.
"Working as a clinical doctor in obstetrics, I often meet women with 'borderline high blood pressure,' and I wanted to find out if they had increased risks of adverse fetal outcomes," says lead author Dr. Anna-Karin Wikström, associate professor of obstetrics at Uppsala.
She and her team recently published their findings in Hypertension - a journal of the American Heart Association (AHA).
Data of more than 150,000 women analyzed
The team assessed the 2008-2014 medical records of more than 150,000 women from the Stockholm-Gotland Obstetric Database.
Only women who carried singleton babies, those who carried their babies for at least 37 weeks and those whose blood pressure did not rise above 140/90 mm/Hg during pregnancy were included in the final analysis.
The researchers assessed the women's blood pressure readings before 20 weeks' gestation and after 34 weeks' gestation, focusing specifically on diastolic blood pressure - the pressure in the arteries between heartbeats.
Additionally, the team assessed the number of small-for-gestational-age (SGA) infants - defined in the study as a birth weight in the lowest 2.5% in a certain gestational week - born to the women, as well as the number of stillbirths.
70% increased stillbirth risk with late-pregnancy prehypertension
Overall, 11% of the women in the study developed prehypertension during pregnancy. There were 194 stillbirths among the women and 2,426 SGA infants.
- In the US, a stillbirth is defined as a fetal loss after 20 weeks of pregnancy
- Each year, around 24,000 stillbirths occur in the US
- Smoking, obesity and pregnancy after 35 years of age are some factors that have been linked to increased risk of stillbirth.
Compared with women whose blood pressure remained normal during pregnancy, those who developed prehypertension from 36 weeks' gestation were 70% more likely to have a stillbirth and 69% more likely to have an underweight infant.
Women whose diastolic blood pressure increased by 15 points during pregnancy were more than twice as likely to give birth to an underweight baby, compared with those with normal blood pressure.
Furthermore, each one-point increase in diastolic blood pressure was associated with a 2% increase in the risk of having an underweight baby - for women with and without prehypertension.
These findings remained after accounting for a number of influential factors, including mother's age, weight, smoking status and diabetes diagnosis.
While the researchers admit that their study is observational and cannot prove a causal link between prehypertension and increased risk of poor fetal outcomes, the findings may act as a warning for women to ensure their blood pressure is controlled during pregnancy.
Last August, Medical News Today reported on a study suggesting children born to mothers who had high blood pressure during pregnancy may be at greater risk for hypertension in later life.