EP08.07: Increase in birthweight at short inter‐pregnancy interval: a populations‐based follow‐up study in Norway

To study mean changes in birthweight from the first to the second delivery according to length of the inter-pregnancy interval. We studied all women and also within sub-groups of the women's age at first delivery. 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. The adjusted mean birthweight increase at <6 moths interval was 227 grams (g) (95% CI; 219g-236g), and Thais was 90g higher than at 6-11 months inter-pregnancy interval (137g (95% CI; 130g-144g)). After exclusion of women with a first stillbirth, the mean increase in birthweight at inter-pregnancy interval <6 months was attenuated (152g, 95% CI; 143g-160g), but remained higher than at longer inter-pregnancy intervals. This finding was particularly prominent in women >35 years (218g, 95% CI; 139g - 298g). In women with a first live born infant weighing <2500g, mean birthweight increased by around 1000g to the second delivery. Also among these women, the increase was most prominent at <6 months inter-pregnancy interval. We found the highest mean increase in birthweight at the shortest inter-pregnancy interval.