Pre-pregnancy body mass index and gestational weight gain in Thai pregnant women as risks for low birth weight and macrosomia

Background and Objectives: Maternal pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) have been reported to be associated with pregnancy outcomes. Due to the nutrition transition in Thailand, the double burden of malnutrition is increasing and this may have negative consequences on birth outcomes. This study aimed to investigate the relationship between pre-pregnancy BMI and GWG with the risks of low birth weight and macrosomia. Methods and Study Design: We performed a secondary analysis of data obtained from an iodine supplementation trial in mildly iodine-deficient Thai pregnant women. Pre-pregnancy BMI was classified using the WHO classification. GWG was categorized using the IOM recommendation. Binary and multinomial logistic regressions were performed. Results: Among 378 pregnant women, the prevalence of pre-pregnancy underweight (BMI < 18.5 kg/m²) and overweight (BMI=25 kg/m²) were 17.2% and 14.3%, respectively. Normal weight women had the highest median GWG [15.0 (12.0, 19.0) kg] when compared to overweight women [13.2 (9.0, 16.3) kg]. Forty-one percent of women had excessive GWG, while 23% of women gained weight inadequately. Women with a high pre-pregnancy BMI had a 7-fold higher risk of having a macrosomic infant. Women who had excessive GWG were 8 times more likely to deliver a newborn with macrosomia. Conclusions: Both high pre-pregnancy maternal weight and excessive weight gain during pregnancy increase risk of infant macrosomia. Therefore, maintaining normal body weight before and throughout pregnancy should be recommended in order to reduce the risk of excessive infant birth weight and its associated complications.