Dad's Diabetes May Affect Newborn's Birth Weight

Fri Jan 3,

By Amy Norton

NEW YORK (Reuters Health) - New research links a father's type 2 diabetes with lower birth weight in his child, supporting the theory that genetic factors underlie both fetal growth and diabetes risk.

UK researchers found that among the more than 8,000 parents they studied, the children of fathers with diabetes were born at an average of 186 grams (about 6.5 ounces) less than those whose fathers were not diabetic.

Unlike the case with mothers, a father's diabetes cannot affect a child's birth weight by influencing the fetal environment during development.

"The link with fathers' diabetes can only plausibly be genetic," study author Dr. George Davey Smith told Reuters Health.

Therefore, the findings support the hypothesis that "common genetic factors" contribute to both type 2 diabetes risk and poorer prenatal growth, according to Smith and his colleagues.

Their report is published in the January 4th issue of the British Medical Journal.

Type 2 diabetes occurs when the body loses its sensitivity to the blood-sugar-regulating hormone insulin, leading to chronically high blood-sugar levels. This form of diabetes often occurs as part of a metabolic syndrome that includes obesity, high blood pressure and high cholesterol.

Past research has suggested that low birth weight--less than 5.5 pounds, or 2.5 kilograms--may raise a person's risk of type 2 diabetes and related conditions later in life. Researchers suspect that part of this association may be explained by the effects that the uterine environment has on a newborn's metabolism and overall hormonal system--effects that may extend into adulthood.

But since a father's diabetes cannot influence the fetal environment, the new findings point toward the importance of genes in the association between birth weight and type 2 diabetes, according to Smith, a researcher at the University of Bristol.

"Fetal growth," he said, "is regulated by insulin-like growth factors--and perhaps insulin--so it would not be surprising if genetic differences in response to insulin were related to both fetal growth and later risk of diabetes."

The findings are based on data from parents who were part of a large UK study of men and women born in 1958. Thirty-four fathers were diabetic, and 24 women had become diabetic sometime after having children.

There was some evidence that these women tended to have lower-weight newborns, although the association was not as clear as that for fathers.

Previous research has shown that women who have diabetes or pre-diabetes metabolic disturbances during pregnancy tend to have bigger babies. According to Smith's team, this likely reflects the direct effects of the mother's metabolic control, which could "mask" the genetic factors that act to reduce fetal growth.

SOURCE: British Medical Journal 2003;326:19-20.

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