Maternal hypertension in utero associated with decreased cognitive ability throughout life and in to old age

Image: PD
Key study points:

1. Men born to mothers that experienced hypertension during pregnancy achieved lower arithmetic and total cognitive scores at age 68.5 compared to controls with normotensive mothers.
2. Men born to hypertensive mothers experienced a greater decline of cognitive ability between ages 20.1 and 68.5.

Primer: The in-utero environment experienced by a fetus can greatly affect its physical and mental development both during pregnancy and after birth. Indeed, studies have shown that intrauterine growth restriction resulting in low birth weights was associated with increased neonatal health problems, higher rates of neurological impairment in childhood, and lower intelligence quotient (IQ) scores. Maternal hypertension, which complicates between 3.6-9.1% of pregnancies, is a particularly common cause of fetal growth retardation, with more severe cases of pregnancy-associated hypertension linked to worse outcomes. However, does maternal hypertension affect cognitive outcomes? If so, for how long? These questions were addressed by a team of researchers using data from the Helsinki Birth Cohort who compared men born to hypertensive mothers with those whose mothers were normotensive during pregnancy. They found that maternal hypertension during pregnancy was associated with lower cognitive scores in men at age ~20. The current study expands on these findings to investigate how the intellectual abilities of these men change as they age compared to their cohorts born to normotensive mothers.
Background reading:

1. Summary of the NHLBI Working Group on Research on Hypertension During Pregnancy [Hypertension]

2. Effect of Very Low Birth Weight and Subnormal Head Size on Cognitive Abilities at School Age [NEJM]

3. Population-based trends in pregnancy hypertension and pre-eclampsia: an international comparative study [BMJ]

4. Pregnancy Outcomes in Healthy Nulliparas Who Developed Hypertension [Obstetrics and Gynecology]

This [retrospective cohort] study: 6,975 men born between 1934 and 1944 in one of two public maternity hospitals in Helsinki, Finland were studied. Maternal hypertension was assessed using blood pressure and urinary protein measurements. Hypertensive disorder in pregnancy was defined to be systolic pressure greater than or equal to 140 mmHg or diastolic pressure greater than or equal to 90 mmHg. Cognitive ability was assessed using the Finnish Defense Forces basic ability test, which was administered before compulsory military service at the average age of 20.1 and again at age 68.5. Of the 6,975 men studied, 398 were born to hypertensive mothers. Statistical analysis revealed that men whose mothers who experienced increased blood pressure during pregnancy scored 4.36 (CI: 1.17-7.55) points lower on their total cognitive ability score at age 68.5 compared to men born to normotensive mothers. Further, these men experienced a greater mean decline in total cognitive ability score between ages 20.1 and 68.5 (-1.66 versus -0.47 in men with normotensive mothers)

In sum: The findings of this study suggest that blood pressure status of the mother during pregnancy can affect intellectual ability of the offspring throughout life. Indeed, maternal hypertension is not only associated with decreased cognitive test scores in both young adulthood and late life, but it is also linked with a greater decline in intellectual ability with age. Thus, maternal hypertension may contribute to the well-known link between intrauterine growth restriction in utero and cognitive problems after birth.

The study does present several limitations. First, the study population was restricted to men only, and thus these findings cannot be generalized to females. Second, men who were lost of follow up or who passed away prior to the second administration of the Finnish Defense Forces basic ability test were not included in the final analysis, thus the results may have been affected by attrition bias. Finally, hypertension is typically diagnosed over 2 elevated blood pressure measurements. However, in this study, the authors categorized maternal hypertension after one supranormal recording, resulting in a greater incidence of hypertension than expected compared to general population rates.
Click to read the study in Neurology

Written by [MK]

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