Mom's blood pressure may affect baby's IQ

Hypertension isn't just risky for a pregnant woman, it can have lasting consequences for a child's cognitive ability, a new study suggests.

A Finnish study found that men whose mothers' pregnancies had complications from hypertensive disorders scored lower on tests of cognitive ability than those whose mothers did not have high blood pressure during pregnancy. The study appears in the journal Neurology .

About 10% of all pregnancies become complicated by hypertensive disorders, such as preeclampsia , the study said. Such conditions are linked to premature births and small baby body size, factors that are also linked with lower cognitive ability.

Methods

Researchers identified 398 men who had taken a basic ability test for the Finnish Defense Forces twice: around age 20 and again around age 69. In this way, study authors were able to look at verbal, arithmetic and visuospatial reasoning scores. Visuospatial means understanding visual representations and their spatial relationships.

Information about the mothers' blood pressure and urinary protein were used to determine which pregnancies were complicated by hypertension.

The study authors had previously shown that men whose mothers had hypertension-complicated pregnancies tended to score lower around the 20-year mark than men whose mothers did not.

Results

Men whose mothers had a hypertensive disorder during pregnancy had worse scores on arithmetic reasoning and total cognitive ability in both young adulthood and old age. This suggests that "a propensity toward lower cognitive ability has its origins in the prenatal period, when the majority of the development of brain structure and function occurs," the study said.

Associations with decline were strongest in math reasoning scores. Men's test scores were on average 4.36 points lower on total thinking ability in old age, and 2.88 points lower at age 20.

Limitations

The study only looked at men, not women, and only in Finland. Also, only men who survived into older age for the second testing were included, so the findings might be biased toward otherwise healthy men.

Also, there was not enough data to require two high blood pressure measurements in order to establish hypertensive disorders, so the authors found higher-than-average incidence of these conditions among the mothers in the study. Additionally, the sample size is somewhat small.

Implications

The results suggest that a person's declines in thinking ability in old age could be tied to his or her mother's high blood pressure disorder in the womb. But this is only an association, not proof. Especially given the limitations of the study, more research is needed to confirm these findings.

In the meantime, separate research is looking at signs for hypertensive disorders in pregnant women.

A recent study in the American Journal of Obstetrics and Gynecology found that women who begin snoring after becoming pregnant may be at increased risk of developing high blood pressure and cardiovascular problems.

Sleeping on the left side is better for pregnant women than sleeping on the back, Louise O'Brien, an associate professor at the University of Michigan's Sleep Disorders Center, told CNN. That's because some of the vessels that return blood to the lungs get pressed down on by the weight of the uterus.

More from CNN Health: Pregnant and didn't know it

CNN's Saundra Young contributed to this report.