The theory that adult health is determined to a significant degree by conditions in the womb before birth has recently been challenged.

The ‘fetal origins of adult disease’ hypothesis says that when a fetus is undernourished, it diverts resources to the most crucial areas for development at the time, like the brain, at the expense of organs it will need later in life, such as the lungs. This, in turn, makes the individual more vulnerable to heart disease and related disorders, such as high blood pressure, stroke and diabetes, in later life.

However, a recent critique concludes that the link between low birth weight and higher blood pressure later in life, an early cornerstone of the theory, may not be as strong as has been believed.

>From past studies and meta-analyses, it was estimated that a 1-kg (2.2 lb) increase in birth weight is typically associated with a 2-4 mmHg reduction in systolic blood pressure in adulthood, with corresponding health benefits.

But a comprehensive re-analysis of 103 studies suggests a reduction of only 0.6 mmHg/kg increase in birth weight.

This, however, is not the final word on the subject. The association between life in the womb and health in later life is a complex one. Proponents of the fetal theory accept the new analysis as constructive criticism, but do not accept the interpretation (Lancet, 2002; 360: 659-65).