The condition is associated with birth complications such as shoulder dystocia, in which the shoulders get stuck during vaginal delivery, and can lead to maternal hemorrhages after birth. Though high maternal birth weight, maternal obesity, diabetes and carrying a baby past term are associated with the condition, until now it has been unclear whether both parents’ birth weight affects the weight of their offspring.
To find out, researchers looked at data from 647,957 sets of babies and parents born in Norway between 1967 and 2002, matching the birth-weight data of parents born between 1967 and 2002 with that of their children, who were born between 1983 and 2017.
Among that group, 3.2 percent of the parents and 4 percent of their children were large babies. The children of parents with macrosomia had a “substantially increased risk” of high birth weight themselves.
If both parents had high birth weights, they had an 8.06 percent higher risk of macrosomia. The risk was also raised by 3.84 percent in cases where only the mother had a high birth weight and 2.34 percent in cases in which only the father had a high birth weight.
Just 3.6 percent of the babies born to parents without high birth weight were large at birth, compared with 23.4 percent of those babies born to parents who did have high birth weights.
Maternal obesity was also linked to a higher birth weight, even in mothers who did not themselves have macrosomia in infancy. Six percent of babies whose parents did not have macrosomia but had an obese mother ended up having a high birth weight, compared with 31 percent for babies whose parents both had macrosomia and whose mother had obesity.
Overall, the researchers write, “parental macrosomia tends to be passed between generations,” though it is unclear to what extent genetics or habits play a role. More research is needed to determine whether screening for past macrosomia could identify high-risk deliveries, and the researchers point out that because their research used Norwegian data, it is not necessarily applicable to other populations.
According to the Centers for Disease Control and Prevention, 7.44 percent of all babies born in the United States in 2021 weighed above 4,000 grams. White parents in the United States were the most likely to give birth to a child with macrosomia.