Background and aims Bariatric surgery (BS) is extensively used and one of few lasting ways to treat obesity. Women in child bearing age also undergo BS; BS-offspring has a lower mean birth weight and an increased risk of being small for gestational age compared to non-BS-offspring. The aim of our study was to assess how BS affects newborn body composition and if BS was associated with offspring aberrant fat deposition.

Methods Pregnant women who previous had Roux-en-Y-gastric-bypass were included. Offspring anthropometric measurements were collected at birth and total and regional newborn body composition was assessed using dual-energy X-ray absorptiometry. The offspring of BS-mothers was compared to offspring of non-BS mothers. Aberrant fat deposition was defined as the percentage of total fat that was placed abdominally. Multiple linear regressions were used to assess the effect of BS.

Results We included 25 BS-offspring and 293 non-BS-offspring for comparison. There was no difference in maternal pre-pregnancy BMI between the groups (p = 0.16). BS-offspring had lower birth weight (-311 g, p = 0.002), lower fat percentage (- 2.6%, p = 0.002), lower lean mass (-260 g, p < 0.001) and a lower percentage of total fat placed abdominally (-1.6%, p = 0.024). The analyses were adjusted for pre-pregnancy obesity, maternal age, parity, gestational weight gain and newborn sex and gestational age.

Conclusion We observed significant differences in body composition between offspring of women with previous BS compared to those without surgery. The BS-offspring had lower birth weight, fat percentage and lean mass. There was no sign of aberrant fat deposition in BS-offspring.