Background An increasing number of childbearing-aged women have undergone bariatric surgery (BS). Although pregnancy outcomes generally improve after BS, concern remains over the impact of rapid weight loss and the catabolic state that occurs soon after BS. At least a 12-month surgery-to-conception time (SCT) is recommended, though the reasoning behind this has been questioned. This retrospective study was conducted to compare post-BS pregnancies with SCTs of less (Group 1) or more (Group 2) than 12 months.

Methods The Hospital Register and Finnish Medical Birth Register were queried for data on BS and subsequent pregnancies. The characteristics of women at surgery and maternal and newborn outcomes in post-BS pregnancies were collected.

Results Between 2010 and 2022, 113 women gave birth after BS. This included 17 and 96 patients in Groups 1 and 2. The mean SCTs were 8.0 +/- 2.7 and 39.0 +/- 24.3 months (p < 0.001), respectively. At BS, the characteristics of age (p = 0.316), weight (p = 0.718), body mass index (BMI) (p = 0.114) and surgical technique used (p = 0.648) were similar. During pregnancy, the mean age of Group 1 women was significantly lower (p = 0.005). With no difference in weight (p = 0.961) or BMI (p = 0.567), the incidence of gestational diabetes mellitus (GDM, p = 0.039) was higher in Group 2. The mean gestational age at delivery (p = 0.206) and incidence rates of preterm (p = 0.645), post-term (p = 1.00) and caesarean deliveries (p = 1.00) in the groups were similar. A significantly higher incidence of delivery induction (p < 0.001 was detected in Group 2. The mean newborn weight in Group 1 was lower (p = 0.038), but the mean birth weight standard deviation (p = 0.883) and incidences of low birth weight (< 2500 g, p = 0.345) and small-for-gestational-age newborns (p = 0.469) were similar. The 1- (p = 0.191) and 5-min (p = 0.174) Apgar points in the groups were similar, and no associations between pregnancy outcomes and surgery technique were detected.

Conclusions The outcome in pregnancies with an SCT 12 months, postponing pregnancy may not always improve pregnancy outcomes. Therefore, all risks should be weighed when counselling women regarding the optimal time of pregnancy after BS.