How to avoid an abnormally large baby

Robin Wulffson MD's picture
macrosomia, large for gestational age, gestational diabetes, risk
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A large-for-gestational-age or macrosomic (unusually large) infant is a risk factor for both mother and infant. Women who suffer from gestational diabetes are prone to have a macrosomic or large-for-gestational-age infant; however, a new study has reported on risk factors for a macrosomic or large-for-gestational-age infant who do not have gestational diabetes.

Researchers affiliated with the University of Toronto (Ontario, Canada), published their findings on May 22 in the Canadian medical Association Journal).

The authors noted that the delivery of excess maternal nutrients to the fetus is known to increase the risk of macrosomia, even among infants of women without gestational diabetes. They explained that the current obesity epidemic in the US and Canada impacts on circulating adipokines and inflammatory proteins, which may in turn stimulate fetal growth. (Adipokines are cell-to-cell signaling proteins secreted by adipose tissue.) The investigators conducted their study to evaluate the independent effects of maternal glycemia (glucose levels), lipids, obesity, adipokines, and inflammation on infant birth weight.

According to the American Congress of Obstetrics and Gynecology (ACOG), macrosomia implies growth beyond a specific weight, usually 4,000 grams (8 pounds, 12 ounces) or 4,500 grams 90 pounds, 15 ounces) regardless of the gestational age. The risks of morbidity for infants and mothers when birth weight is between 4,000 grams and 4,500 grams are greater than those of the general obstetric population, these risks increase sharply beyond 4,500 grams. Recent large cohort studies further support the continued use of 4,500 grams as an appropriate estimated weight beyond which the fetus should be considered macrosomic. The term large for gestational age generally implies a birth weight equal to or greater than the 90th percentile for a given gestational age.

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The study group was comprised of 472 women who underwent an oral glucose tolerance test in late pregnancy and were found not to have gestational diabetes; however, 104 (22.0%) had gestational impaired glucose tolerance. The investigators also measured fasting levels of insulin, low- and high-density lipoprotein cholesterol, triglycerides, leptin, adiponectin, and C-reactive protein. Obstetric outcomes were evaluated at delivery.

The average birth weight was 3,481 grams (7 pounds, 10 ounces); 68 of the infants were large for gestational age. The investigators found that positive determinants of birth weight were length of gestation, male infant, weight gain during pregnancy up to the time of the oral glucose tolerance test, body mass index (BMI) before pregnancy, and impaired glucose tolerance in pregnancy. Leptin, adiponectin, and C-reactive protein levels were each negatively associated with birth weight. They found that the significant metabolic predictors of having a large-for-gestational-age infant were BMI before pregnancy, weight gain during pregnancy up to the time of the oral glucose tolerance test, and leptin level.

The authors concluded that among women without gestational diabetes, maternal adiposity, and leptin levels were the strongest metabolic determinants of having a large-for-gestational-age infant rather than glucose intolerance and lipid levels.

Take home message:
In view of this study, it would be prudent for overweight women to undergo a weight reduction program before pregnancy. Even if a woman begins pregnancy with a normal BMI, she should avoid excessive weight gain during pregnancy. Large infants increase the likelihood of a cesarean or instrumented delivery (forceps or vacuum), which places both infant and mother at increased risk. Many pregnancy complications increase in overweight women, including preeclampsia (toxemia) and pregnancy induced hypertension.

Reference: Canadian Medical Association Journal

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