London New research adds to a growing body of evidence that adult health is set to a significant degree by conditions in the womb and suggests the programming may start earlier in pregnancy than previously believed.
A study published this week in the Journal of Epidemiology and Community Health found that fetuses with shorter thigh bones at 24 weeks had higher blood pressure at the age of 6 than those with longer thigh bones.
Understanding how life in the womb influences later health has become a hot area of medical research. It has focused mostly on the effect of birth weight on health and the subsequent development of illnesses such as heart disease, high blood pressure, diabetes and osteoporosis. But the latest study is among the first to find evidence earlier in human life.
Scientists believe that when a fetus is undernourished, it diverts resources to areas it really needs at the time, such as the brain, at the expense of organs it will need later in life. That may permanently change the baby's structure, functioning and metabolism, experts believe.
"There's a lot of work about the size at birth," said Dr. David Barker, an epidemiologist who pioneered fetal programming research but was not involved in the latest study. "Birth weight is a crude measurement. It tells you very little because babies can reach the same birth weight by many different paths of growth.
"Now, because of technology advances, people are able to study children who have had serial measurements of size in (the uterus) that follow their growth, and these observations take us back into early pregnancy," said Barker, director of the epidemiology unit at the University of Southampton in England. "It looks as though blood pressure may be set fairly early."
The study, led by Dr. Kevin Blake at the University of Western Australia, involved ultrasounds done at 18, 24, 28, 34 and 38 weeks of pregnancy on 707 women with normal pregnancies. During each scan, doctors measured the circumference of the head and abdomen and the length of the babies' thigh bones.
Blood pressure was measured in about 300 of the resulting children at age 6.
The researchers found that for every one-tenth of an inch deviation from the typical thigh bone length at key stages in the womb, systolic blood pressure the higher of the two numbers was changed by about 2 points. Shorter thighs meant higher blood pressure.
That effect was first seen at 24 weeks of pregnancy.
Neither head nor abdomen circumference was linked to later blood pressure.