The impact of gestational weight gain and nutritional intake on small for gestational age in twin pregnancies: A multicenter prospective cohort study in Japan

Abstract

Purpose

Small for gestational age (SGA) is defined as a birth weight below the 10th percentile for gestational age, with a higher incidence in twin pregnancies compared to singletons. Preventing SGA is crucial due to its short-term risks, such as delayed adaptation to extrauterine life, and long-term risks like adult lifestyle diseases. Factors contributing to SGA in twin pregnancies include chorionicity, twin-to-twin transfusion syndrome, hypertensive disorders, smoking, pre-pregnancy body mass index (BMI), and gestational weight gain (GWG). Additionally, nutritional intake is likely associated with SGA, as previous studies have shown that nutrients promote fetal growth. In Japan, the guidelines for GWG established in the United States are not widely applicable, and there are no standardized recommendations for GWG and nutritional intake during twin pregnancies. This study aimed to examine the various factors that contribute to SGA in twin pregnancies, with a specific focus on GWG and nutritional intake.

Methods

This study was part of the Japan Pregnancy Eating and Activity Cohort Study, conducted across four regions in Japan; however, participants in this particular study were drawn from three of those regions. The recruitment phase spanned March 2020 and February 2024. Inclusion criteria were pregnant women with twins, and exclusion criteria were those with miscarriages or missing infant data. Data collection included questionnaires on maternal lifestyle, nutritional intake, and supplement use, alongside medical records for birth outcomes and maternal characteristics. Participants were grouped into SGA or appropriate for gestational age (AGA). GWG during pregnancy was assessed cumulatively and weekly by trimester, while dietary intake of nutrients, such as iron, folic acid, and omega fatty acids, was analyzed using a brief-type self-administered diet history questionnaire. Additional data included maternal demographics, pre-pregnancy BMI, pregnancy complications, twin chorionicity, and nausea severity measured by the pregnancy-unique quantification of emesis and nausea scale.

Results

This study included 20 (29.4%) and 48 (70.6%) participants in the SGA and AGA groups, respectively. In the SGA group, The SGA group had a significantly lower pre-pregnancy BMI and a higher number of underweight women than the AGA group (p = .002 and p = .027). Underweight women in the SGA group exhibited lower weekly GWG of 340 g during the third trimester (p = .030). However, no significant differences in nutritional intake were observed between the groups.

Conclusion

Exploration of SGA factors in twin pregnancies linked pre-pregnancy BMI and third-trimester GWG in underweight women to SGA, with no association found for nutritional intake. Emphasizing healthy BMI and appropriate third-trimester GWG for underweight women is crucial. Future studies should expand sample sizes and differentiate monochorionic diamniotic and DD twins to update health guidelines.