BackgroundExcessive gestational weight gain (GWG) is associated with adverse maternal-child health outcomes. Managing energy intake and GWG versus optimising nutrient intake can be challenging. The present study aimed to examine the relationships between dietary portion size, GWG and nutrient intakes during pregnancy. It is hypothesised that, after adjustment for potential confounders, portion size would be positively associated with both GWG and nutrient intakes during pregnancy. MethodsProspective data were obtained for 179 Australian women from the Women and Their Children's Health Study. A validated food frequency questionnaire was used at 18-24 and 36-40weeks of gestation to quantify diet and portion size during the previous 3months of pregnancy. Nutrient intakes were compared with Australian Nutrient Reference Values (NRVs). GWG was measured up to 36weeks and compared with the Institute of Medicine weight gain recommendations (WtAdh). ResultsIn multivariate regression models, portion size factor (PSF) was positively associated with GWG in women with high socio-economic status (SES; =0.20, P=0.04) and those with an overweight/obese pre-pregnancy body mass index (BMI) (=0.28, P=0.04). PSF uniquely accounted for 8.2% and 3.7% of the variability in GWG for women with high SES and overweight/obese pre-pregnancy BMIs, respectively. Nutrient intakes and PSF were similar regardless of WtAdh. Women achieved NRVs for calcium and zinc in all PSF categories. Most of the women with large PSF still failed to achieve the NRVs for folate (95.7%), iron (89.6%) and fibre (85.5%). ConclusionsAll women require advice on quality food choices during pregnancy to optimise health outcomes. Targeting portion size alone is insufficient to manage GWG but may prove to be a valuable tool in pregnant women of high SES and/or those who are overweight/obese pre-pregnancy.