Purpose Current guidelines recommend to avoid pregnancy for 12–24 months after bariatric surgery because of active weight loss and an increased risk of nutritional deficiencies. However, high-quality evidence is lacking, and only a few studies included data on gestational weight gain. We therefore evaluated pregnancy and neonatal outcomes by both surgery-to-conception interval and gestational weight gain. Materials and Methods A multicenter retrospective analysis of 196 singleton pregnancies following Roux-en-Y gastric bypass, sleeve gastrectomy, and one anastomosis gastric bypass was conducted. Pregnancies were divided into the early group (≤ 12 months), the middle group (12–24 months), and the late group (> 24 months) according to the surgery-to-conception interval. Gestational weight gain was classified as inadequate, adequate, or excessive according to the National Academy of Medicine recommendations. Results Pregnancy in the early group (23.5%) was associated with lower gestational age at delivery (267.1 ± 19.9 days vs 272.7 ± 9.2 and 273.1 ± 13.5 days, P = 0.029), lower gestational weight gain (− 0.9 ± 11.0 kg vs + 10.2 ± 5.6 and + 10.0 ± 6.4 kg, P < 0.001), and lower neonatal birth weight (2979 ± 470 g vs 3161 ± 481 and 3211 ± 465 g, P = 0.008) than pregnancy in the middle and late group. Inadequate gestational weight gain (40.6%) was associated with lower gestational age at delivery (266.5 ± 20.2 days vs 273.8 ± 8.4 days, P = 0.002) and lower neonatal birth weight (3061 ± 511 g vs 3217 ± 479 g, P = 0.053) compared to adequate weight gain. Preterm births were also more frequently observed in this group (15.9% vs 6.0%, P = 0.037). Conclusion Our findings support the recommendation to avoid pregnancy for 12 months after bariatric surgery. Specific attention is needed on achieving adequate gestational weight gain.