Thigh length of babies in the womb linked to later childhood health

The thigh length of babies in the womb is as strong an indicator of subsequent childhood – and potentially adult – blood pressure as birthweight, suggests a study in the Journal of Epidemiology and Community Health.

Researchers scanned 707 developing fetuses to measure the dimensions of their abdomen and head circumferences and the length of the thigh bones (femurs). The growing babies were scanned five times each between 18 and 38 weeks of pregnancy. Blood pressure was then measured in 300 of the children from these pregnancies when they were 6 years old.

The results confirmed the now well-established finding that low birth weight is strongly associated with higher systolic blood pressure in childhood. But, equally, they also showed that shorter thigh bones at 24 weeks of pregnancy were associated with higher systolic blood pressure at the age of 6.

The lowest childhood blood pressures were found in those who had weighed the most at birth, whose abdomens grew reasonably or very fast in the womb, and whose thigh bones were longest at 24 weeks. For the longest 5 per cent of femurs, there was a significant 1 to 2 mm Hg decrease in systolic blood pressure.

The effect of fetal femur length at 24 weeks paralleled that of abdominal circumference, which is a strong marker of growth in mid to late pregnancy, because it reflects liver size and subcutaneous fat, which in turn point to how well nourished the mother and fetus are.

This is important, say the authors, because it suggests the ‘fetal programming’ of subsequent childhood and adult health may start earlier in pregnancy than previously thought, and may not be related to maternal nutrition in later pregnancy.