Fat loss during pregnancy may not prevent LGA babies

Interventions intended to help pregnant women lose weight may not prevent large-for-gestational-age (LGA) newborns, a study of 2618 women has found.

Researchers at the UCD Centre for Human Reproduction at Coombe Women and Infants University Hospital in Dublin, Ireland, recruited nondiabetic women after ultrasound confirmation of an ongoing singleton pregnancy in the first trimester. They hoped to estimate whether maternal fat mass measured in the first trimester correlated better with birth weight than did fat-free mass, and to identify which maternal body composition parameters correlated best with birth weight.

Maternal body composition was measured using bioelectric impedance analysis. Multivariable linear regression analysis was performed to identify the strongest predictors of birth weight, with multiple logistic regression analysis performed to assess predictors of birth weight greater than 4 kg (8 lb 13.09 oz).

Of the 2618 women, 49.6% (n=1075) were primigravid and 16.5% (n=432) were obese based on a body mass index (BMI) of 30 or higher. In univariable analysis, maternal age, BMI, parity, gestational age at delivery, smoking, fat mass, and fat-free mass all correlated significantly with birth weight. In multivariable regression analysis, fat-free mass remained a significant predictor of birth weight (P<.001), but notably, no relationship was found between maternal fat mass and birth weight, the researchers reported. After adjustment for confounding variables, women in the highest fat-free mass quartile had an adjusted odds ratio of 3.64 (95% confidence interval 2.34–5.68) for a birth weight more than 4 kg compared with those in the lowest quartile.

In an article published in the January 2013 issue of Obstetrics & Gynecology, the researchers conclude, “there is a potential risk that overzealous attempts to reduce gestational weight gain in obese women may cause complications by reducing calorie intake or micronutrients. This reduction may be detrimental to the fetus and, in the absence of gestational diabetes mellitus, our results suggest minimizing maternal weight gain may not prevent fetal macrosomia and could potentially increase the risk of intrauterine growth restriction.”