Patterns of gestational weight gain in healthy, low-risk pregnant women without co-morbidities.

Background: little is known of the impact of gestational weight gain (GWG) in relation to Body Mass Index (BMI) classification on perinatal outcomes in healthy pregnant women without co-morbidities. As a first step, the prevalence of obesity and the distribution of GWG in relation to the Institute of Medicine (IOM) 2009 guidelines for GWG were examined.

Methods: data from a prospective cohort study of - a priori - low risk, pregnant women from five midwife-led practices (n=1449) were analysed. Weight was measured at 12, 24 and 36 weeks.

Findings: at 12 weeks, 1.4% of the women were underweight, 53.8% had a normal weight, 29.6% were overweight, and 15.1% were obese according to the WHO classification of BMI. In our study population, 60% of the women did not meet the IOM recommendations: 33.4% had insufficient GWG and 26.7% gained too much weight. Although BMI was negatively correlated to total GWG (p<.001), overweight and obese women class I had a significant higher risk of exceeding the IOM guidelines. Normal weight women had a significantly higher risk of gaining less weight than recommended. Obese women classes II and III were at risk in both over- and undergaining.

Conclusions: our data showed that the majority of women were unable to stay within recommended GWG ranges without additional interventions. The effects on pregnancy and health outcomes of falling out the IOM guidelines remain unclear for - a priori - low risk women. Since interventions to control GWG would have considerable impact on women and caregivers, harms and benefits should be well-considered before implementation.