Pre-pregnancy body mass index, maternal weight gain during pregnancy and risk of small-for-gestational age birth: Results from a case-control study in Italy

Objective. To analyze the association between body mass index (BMI), gestational weight gain (GWG), and risk of small for gestational age (SGA) birth. Methods. Case-control study: cases included 555 women (mean age 31 years) who delivered SGA babies in two Italian clinics. Controls included women who gave birth at term to healthy infants of normal weight at the hospitals where cases had been identified. Results. Underweight women were at risk of delivering SGA babies (odds ratio, OR, 1.9, 95% confidence interval, CI, 1.6-2.4) and overweight women had a not significant lower risk (OR 0.7, 95% CI 0.5-1.0). The risk of delivering an SGA baby was higher also for women with less than recommended GWG (OR 1.4, 95% CI 1.1-1.9), whereas gaining more than recommended weight was not significantly protective (OR 0.7, 95% CI 0.5-1.0). The analysis in strata of BMI showed that GWG played a significant role, whereas in strata of GWG pre-pregnancy BMI seemed less important. Conclusion. These results suggest that achieving the adequate weight gain during pregnancy, as recommended by IOM, protects against the risk of delivering an SGA infant also in underweight women.