We studied mean changes in birthweight from the first to the second delivery according to length of the inter-pregnancy interval. We also studied recurrence risk of low birthweight, preterm birth and perinatal death. We followed all women in Norway from their first to their second singleton delivery at gestational week 22 or beyond during the years 1970–2019, a total of 654 100 women. Data were obtained from the Medical Birth Registry of Norway. Mean birthweight increased from the first to the second delivery, and the increase was highest in pregnancies conceived < 6 months after the first delivery; adjusted mean birthweight increase 227 g (g) (95% CI; 219–236 g), 90 g higher than in pregnancies conceived 6–11 months after the first delivery (137 g (95% CI; 130–144 g)). After exclusion of women with a first stillbirth, the mean increase in birthweight at inter-pregnancy interval < 6 months was attenuated (152 g, 95% CI; 143–160 g), but remained higher than at longer inter-pregnancy intervals. This finding was particularly prominent in women > 35 years (218 g, 95% CI; 139 –298 g). In women with a first live born infant weighing < 2500 g, mean birthweight increased by around 1000 g to the second delivery, and the increase was most prominent at < 6 months inter-pregnancy interval. We found increased recurrence risk of preterm birth at inter-pregnancy interval < 6 months, but no increased recurrence risk of low birthweight, small for gestational age infant or perinatal death. In conclusion, we found the highest mean increase in birthweight when the inter-pregnancy interval was short. Our results do not generally discourage short pregnancy intervals.

我们根据妊娠间隔的长度研究了从第一次分娩到第二次分娩的出生体重的平均变化。我们还研究了低出生体重、早产和围产期死亡的复发风险。我们在 1970 年至 2019 年期间对挪威所有女性从妊娠第 22 周或之后的第一次单胎分娩到第二次单胎分娩进行了追踪，总共有 654 100 名女性。数据来自挪威医学出生登记处。从第一次分娩到第二次分娩，平均出生体重有所增加，并且第一次分娩后 6 个月受孕 < 的妊娠增加幅度最高；调整后的平均出生体重增加 227 克 (g) (95% CI; 219–236 g)，比首次分娩后 6–11 个月怀孕的怀孕体重 (137 g (95% CI; 130–144 g)) 高 90 克。排除第一次死产的妇女后，妊娠间隔 < 6 个月时出生体重的平均增长有所减弱（152 g，95% CI；143-160 g），但仍高于妊娠间隔较长的情况。这一发现在 > 35 岁女性中尤为突出（218 g，95% CI；139 –298 g）。在第一个活产婴儿体重为 < 2500 g 的女性中，第二次分娩时平均出生体重增加了约 1000 g，并且增加在 < 6 个月妊娠间隔时最为显着。我们发现，妊娠间隔< 6个月时，早产复发风险增加，但低出生体重、小于胎龄儿或围产期死亡的复发风险没有增加。总之，我们发现当妊娠间隔较短时，出生体重的平均增幅最高。我们的结果通常不会阻止较短的怀孕间隔。