Large Weight Gain in Pregnancy Tied to Increased Infant Size

Jenni Laidman

April 17, 2012

April 17, 2012 — Obese mothers who gain excessive weight during pregnancy are nearly 7 times more likely to give birth to a large infant at risk for a lifetime of obesity. Moreover, excess gestational weight gain (GWG) increases the risk of having a large infant, even in mothers who have a healthy prepregnancy body mass index (BMI), according to a study published April 17 in the Journal of Maternal-Fetal and Neonatal Medicine.

The study, by Zachary M. Ferraro from the Healthy Active Living and Obesity Research Group, Children's Hospital of Eastern Ontario Research Institute, Ottawa, Canada, and colleagues, showed that overweight and obesity were associated with an increased risk of having a child considered large for gestational age (LGA) — a risk factor in future obesity. The risk of having an LGA infant increased dramatically if an overweight mother gained more weight during pregnancy then recommended by Institute of Medicine (IOM) guidelines.

The researchers analyzed data from 4321 mother-infant pairs recruited from 2002 to 2009 in the Ottawa and Kingston Birth Cohort. Their goal was to determine the effect of maternal weight and weight gain during pregnancy on the likelihood of giving birth to a child weighing more than 4000 g (8.8 pounds), which puts the child in the 90th percentile for infant weight.

Mothers who reported a prepregnancy BMI indicating overweight — 25 to 29.9 kg/m2 — were nearly twice as likely to give birth to an LGA infant (odds ratio [OR], 1.99; 95% confidence interval [CI], 1.17 - 3.37) as women of healthy weight. For obese women, with a BMI of 30 kg/m2 or more, the OR was 2.64 (95% CI, 1.59 - 4.39).

If a mother's GWG exceeded IOM guidelines, the risk of having an LGA infant increased for women of any weight at pregnancy, (OR, 2.86; 95% CI, 2.09 - 3.92), after adjustment for a mother’s prepregnancy BMI, age, smoking, and maternal height. The problem was compounded if a woman was already overweight or obese: ORs were 3.59 for overweight women (95% CI, 2.60 - 4.95) and 6.71 for obese women (95% CI, 4.83 - 9.31).

"Obesity can become part of an intergenerational cycle," Kristi Adamo, MSc, PhD, coauthor of this report, said in a news release from the University of Ottawa. Dr. Adamo is also the cofounder of the Healthy Active Living and Obesity Research Group at Children's Hospital of Eastern Ontario Research Institute.

"Birth weight averages can be an indicator of the weight a child will carry through preschool and even into adulthood. It's critical for a mother to understand that her healthy eating and lifestyle decisions during pregnancy will impact much more than a nine-month gestation period," she continued.

The adjusted analysis also found smoking mothers were less likely than nonsmokers to deliver an LGA infant (OR, 0.53; 95% CI, 0.35 - 0.79). Parity was associated with an increased risk for an LGA infant (OR, 1.49; 95% CI, 1.22 - 1.82).

The range of acceptable weight gain during pregnancy recommended by the IOM changes according to a mother's weight at the time of pregnancy. Women considered underweight, with a BMI less than 18.5 kg/m2, should gain 12.5 to 18 kg (28 to 40 pounds). Healthy-weight women — BMI of 18.5 to 24.9 kg/m2 — should gain 11.5 to 16 kg (25 to 35 pounds). Overweight women are advised to gain 7 to 11.5 kg (15 to 25 pounds), and obese women, 5 to 9 kg (11 to 20 pounds).

In the study, only 29.3% of the women stayed within IOM GWG guidelines. Another 57.7% exceeded the recommendations. Before pregnancy, 23.7% of women in the study were overweight, and another 16.2% were obese.

"We have shown that the majority of women in our birth cohort population entered pregnancy at an unhealthy weight and gained in excess of recommendations during gestation," the authors noted. "At any weight, excessive GWG has a significant effect on the likelihood that their child will be born LGA, and research has demonstrated that size at birth contributes to obesity development down-stream."

The Canada Ministry of Research and Innovation–Early Researcher Award helped support doctoral training of Zachary Ferraro, who is also supported by an Ontario Graduate Scholarship. Coauthor Dr. Mark Walker is a Canadian Institutes of Health Research (CIHR) New Investigator. Coauthor Shi Wu Wen is a recipient of Ontario Women's Health Council-CIHR Mid-Career Salary Award.

J Matern Fetal Neonatal Med. 2012;25:538-542. Abstract

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