Parents' birthweight tied to prematurity risk

NEW YORK (Reuters Health) - When a father was born large and a mother born small, their baby may be at heightened risk of premature birth, a study suggests.

Past studies have found that children's birthweights tend to be similar to that of their parents, particularly their mother's. But one recent study found that infants whose fathers were born at particularly high birthweights were more likely than other newborns to be delivered prematurely.

The finding was unexpected, and the new study sought to investigate it further.

What it found was that infants of fathers with a high birthweight were, in fact, more likely to be premature -- but only if their mothers were born at a relatively low weight.

The reasons for the findings are not yet clear, according to Dr. Mark A. Klebanoff, a researcher at the National Institute of Child Health and Human Development who conducted the study.

One possibility is that the fetus may grow more rapidly than the mother's uterus can accommodate it, triggering preterm labor, he reports in the American Journal of Obstetrics & Gynecology.

Klebanoff based his findings on data from a study of 1,288 Danish women who gave birth between 1974 and 1989. Overall, he found that paternal birthweight was not related to the odds of preterm birth.

But there was evidence of an interaction between mothers' and fathers' birthweights.

A higher preterm birth risk was seen when the father's birthweight topped 8 pounds, 13 ounces and mothers' was below 6 pounds, 10 ounces. Among these infants, 16 percent were premature. That was roughly twice the rate of infants whose parents both had more moderate birthweights.

According to Klebanoff, more research is needed to confirm these findings, and to understand the underlying reasons.

It's also unclear what the clinical importance of the current findings might be, he notes. While the risk of preterm delivery was higher when fathers were born large and mothers were born small, their children were, on average, born only 5 days sooner than other children.

SOURCE: American Journal of Obstetrics & Gynecology, January 2008.