New research from Children of the 90s indicates that the rate at which blood pressure changes during pregnancy is different for women with normal pregnancies and those who develop blood pressure problems.

Women whose blood pressure becomes high as a result of being pregnant are more at risk of stillbirth, delivering preterm or having a low birth weight baby. High blood pressure as a result of pregnancy, known as hypertensive disorders of pregnancy (HDP), can be the less severe gestational hypertension or the more severe preeclampsia which can, in rare cases, lead to the death of the mother.

Using data on 13,000 pregnant women in Children of the 90s, researchers from the universities of Bristol and Glasgow have found that women who develop either gestational hypertension or preeclampsia have different patterns of blood pressure throughout pregnancy, than women who do not, and that these changes are evident from early in pregnancy. Their findings suggest that monitoring blood pressure changes in early pregnancy may help in the detection of preeclampsia.

In normal pregnancy, blood pressure falls during the first four to five months and then rises until delivery. Women who have high blood pressure in the second half of pregnancy are diagnosed as having what is known as a hypertensive (high blood pressure) disorder of pregnancy. This can be either gestational hypertension, which is defined by blood pressure levels alone, or preeclampsia, defined by high blood pressure along with protein in the urine (proteinuria).

In this study, women who had existing high blood pressure prior to pregnancy, and those who developed gestational hypertension or preeclampsia during their pregnancy had higher blood pressure from very early in pregnancy (2 months) than women with normal pregnancies.

In addition to this, the researchers found that women who developed gestational hypertension had a smaller decrease in blood pressure in the first half of pregnancy, and that women who developed gestational hypertension or preeclampsia, or who had hypertension prior to pregnancy, had a greater increase in blood pressure from mid-pregnancy onwards than women who did not have existing high blood pressure or HDP. Blood pressure rose most rapidly in women who developed preeclampsia than in any other group.

They also found that women who had a greater rise in blood pressure in the second half of pregnancy delivered earlier on average.

These findings suggest that changes in blood pressure may provide an early indication of which women are at risk of developing a HDP, before their blood pressure becomes high enough for diagnosis of these conditions. They also suggest that monitoring changes in blood pressure from early pregnancy onwards, as well as blood pressure levels, may help to identify women who are at risk of problems in their pregnancies.

The study’s lead author, Corrie Macdonald-Wallis, said:

‘Other studies have shown that women with higher blood pressure either prior to or early in pregnancy are at greater risk of developing gestational hypertension or preeclampsia. Our findings also point to rates of change in blood pressure early in pregnancy as potentially useful indicators of a pregnant woman’s risk of these conditions.’

‘Preeclampsia and blood pressure problems during pregnancy are a leading cause of prematurity. The results from this study could help in the early identification of women at risk of complications and ensure that they and their babies receive the best possible care.’