Cleft lip or palate occurs when the tissues that form the palate, or roof of the mouth, and the upper lip do not join correctly. Surgery is often performed to repair the condition.
"We found that large increases in maternal body weight between the first and the second pregnancies were associated with greater risk of having a baby with cleft palate," lead investigator Dr. Eduardo Villamor told Reuters Health.
Villamor, of the Harvard School of Public Health, Boston and colleagues studied data on more than 220 000 Swedish women who had had their first two pregnancies between 1992 and 2004.
The researchers estimated the risk of oral clefts in the subjects' offspring in relation to the maternal change in body mass index (BMI) from the beginning of the first pregnancy to the beginning of the second.
In women whose BMI rose by three or more units in this interval, the adjusted risk of isolated cleft palate was 2,3 times higher than in those who had no substantial BMI change. However, change in BMI was not related to the risk of cleft lip.
Although the mechanisms to explain the association between cleft palate and maternal weight gain between pregnancies are still uncertain, Villamor noted, "this finding contributes additional evidence to the importance of keeping a healthy weight throughout life."
Unexpectedly, the research also suggests an association between isolated cleft palate risk and longer interval between pregnancies. There was a linear increase from 0,3 per 1 000 live births in women with intervals of less than one year to 0,9 in those with an interval of four years or more.