A newborn's birth weight and a mother's weight after pregnancy are influenced not just by how much weight mom gains during pregnancy, but by the source of her excess weight as well, according to new research.
During pregnancy, women gain weight as both fat and lean mass, including weight from water and protein. And although women need to gain enough weight during pregnancy to produce a healthy-sized infant, U.S. investigators found that only increases in lean mass, and not fat mass, appeared to influence infant size.
The study found that women who gained larger amounts of fat during pregnancy had more excess fat after delivery than those who gained less pregnancy weight in the form of fat. The researchers emphasized that a certain amount of fat gain during pregnancy is normal. However, excessive gains in fat mass that may linger beyond pregnancy come from gaining an excessive amount of weight during pregnancy.
Gains in lean mass had no influence on a woman's post-pregnancy weight. In fact, the amount of lean mass gained during pregnancy is critical to her newborn's health.
Researchers have long known that too little or too much weight gain during pregnancy can harm both a mother and her newborn. As a result, the Institute of Medicine has recommended that American women of normal weight gain an average of around 25 to 35 pounds during pregnancy, and that underweight women gain even more.
Gaining too much weight during pregnancy can increase the risk of gestational diabetes, preeclampsia and difficulties during delivery. Gestational diabetes can lead to the birth of a larger-than-normal baby, while preeclampsia, which is characterized by dangerously high blood pressure, can progress to a more serious, seizure-inducing condition. Gaining too little weight during pregnancy can result in babies being born with a low birth weight, which is associated with health problems for the infant.
While weight gain in pregnancy includes increases in both lean mass and fat mass, women with excessive overall weight gains packed on a larger proportion of fat, relative to lean mass, than women who gained a healthy amount.
Regardless of how much fat women gained during pregnancy, only lean body mass appeared to influence the size of the infant, with women who gained more lean body mass giving birth to larger infants.
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