The relationships between maternal nutritional and metabolic parameters and birth weight differ after Roux-en-Y...

Factors influencing fetal growth after metabolic bariatric surgery remain to be clarified.

To evaluate the relationships between birth weight (BW) and maternal nutritional and metabolic parameters after Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG).

University Hospital, France.

Women with a singleton pregnancy who underwent at least one second-trimester nutritional assessment at our institution between 2006 and 2022 were included. Associations between maternal parameters and BW adjusted for sex and gestational age (Z-score) were studied.

A total of 155 pregnancies were studied, 71 after RYGB and 84 after SG. Although postoperative weight loss was greater after RYGB, maternal characteristics before pregnancy were comparable. The number of nutritional deficiencies was similar but women after RYGB took more nutritional supplements, while gestational weight gain was greater after SG. Mean BW (3095 ± 628 g versus 3184 ± 516 g) and the proportion of small-for-gestational-age (SGA) newborns (24% versus 21%) were similar between procedures. No association was observed between nutritional deficits and BW. After RYGB, serum iron parameters were negatively correlated with BW Z-score, while fasting glucose and insulin concentrations were positively correlated (P < .01). No significant associations were identified after SG.

Despite a similar risk of SGA, the maternal determinants of BW differ between RYGB and SG. Metabolic parameters appear to be involved after RYGB but not after SG, whereas nutritional deficiencies do not seem to be associated with BW. Additional maternal factors, particularly after SG, should be investigated to explain the increased risk of SGA.