Higher maternal blood pressure increases risk of pregnancy complications, study finds

Higher maternal blood pressure is linked to more pregnancy complications, a large genetic study of over 700,000 pregnant women has found.

Helping women to keep their blood pressure at normal levels could reduce their risk of experiencing pregnancy complications, the researchers concluded.

Fernanda Morales-Berstein is research associate and lead author.

Morales-Berstein said: “Our findings suggest that higher maternal blood pressure increases the risk of multiple adverse pregnancy outcomes, including preterm delivery, giving birth to smaller babies, needing to have labour induced, gestational diabetes and the baby needing to be admitted to a neonatal intensive care unit.”

Several studies have shown links between high blood pressure in pregnancy and health risks for mother and baby, but most have been observational and cannot separate correlation from causation.

Unmeasured factors, such as socioeconomic position and body weight, may bias results.

Although some trials have tested blood pressure reduction in pregnancy, many have been too small to show clear effects on specific complications for mothers or babies.

The team used Mendelian randomisation, a genetics-based method that helps infer cause and effect, previously applied to maternal blood pressure and outcomes like birthweight and gestational duration, though past results have been inconsistent.

To address the gaps, researchers at the MRC Integrative Epidemiology Unit at the University of Bristol and the Norwegian Institute of Public Health ran the largest Mendelian randomisation study to date, assessing links between maternal blood pressure and 24 adverse pregnancy outcomes.

Using data from more than 700,000 pregnant women, they found that higher maternal blood pressure increases the risk of multiple complications.

For example, a 10 mmHg higher systolic blood pressure was linked to an 11 per cent higher risk of labour induction and a 12 per cent higher risk of preterm delivery.

Carolina Borges is associate professor in aetiological epidemiology at the University of Bristol and joint last author.

She said: “By using genetic information to better isolate cause and effect, our study helps clarify whether a mother’s blood pressure itself contributes to pregnancy and newborn complications.

“This matters for clinical care and public health, as it strengthens the evidence base needed to guide prevention, monitoring, and treatment strategies aimed at improving maternal and infant outcomes.”

The authors said the findings should inform targeted policies to improve maternal and child health in the UK and beyond.

They also called for more research in non-European populations, and for clinical trials to determine the best timing, medicines and doses to prevent complications linked to raised maternal blood pressure.