Having a father who was a small infant more than triples the chances that a baby will also be born small. Furthermore, if this is the case for the mother as well, the likelihood is over 16 times greater, according to study findings reported by French and US researchers.

The study results, which found the influence of both parents to be roughly equal and multiplicative, strongly suggest a genetic reason for the tendency of “small-for-gestational-age” babies to run in families.

It also raises the question of whether such a tendency should be considered a medical problem or a normal variation in growth, Dr. Delphine Jacquet of Hopital Robert Debre in Paris and colleagues write in the women’s health journal BJOG.

There has been extensive research on the effect of a mother’s birth size on infant birthweight, but little information exists on whether the father’s birth size has any bearing on the matter, Jacquet and her team point out.

They investigated the influence of paternal and maternal size at birth on a group of 256 infants. They found infants whose mothers had been small-for-gestational-age were 4.7 times more likely to be small at birth themselves.

The risk was increased 3.5-fold with a small-for-gestational-age father.

Having both parents who were small babies multiplied an infant’s risk by 16.3.

The investigators found no significant interaction between the parents’ size at birth and pregnancy factors known to increase the risk of having a small-for-gestational-age baby, such as the mother Smoking or pregnancy-related high blood pressure.

It’s now necessary to look further into families that tend to have small babies “to investigate whether it results or not from a normal variation in fetal growth,” the researchers conclude.

SOURCE: BJOG, February 2005.

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