The associations of short birth intervals with pregnancy outcomes: population-based cohort study

Short interpregnancy interval has been linked to adverse pregnancy outcomes. WHO recommends waiting at least 2 years after a live birth and 6 months after miscarriage or induced termination before conception of another pregnancy. The objective of the study was to assess association of short interpregnancy interval and pregnancy outcomes. Data source was Medical Birth Register. A total of 51,109 mothers who gave birth between 1 January 2000 and 31 December 2017 were selected for the study. The analysis include women who have had a single pregnancy in the first birth and no stillbirths and abortions in the anamnesis. Interpregnancy interval was defined as the time between the end of pregnancy (delivery date) and the start of the next pregnancy (delivery date of next pregnancy minus gestational age at birth). Adjusted Odds (ORadj) ratio were calculated. Compared with an interpregnancy interval of 18-23 months, intervals shorter than 6-11 and ≤5 months associated with increased odds of preterm births, accordingly ORadj 1.5 (95%CI 1.2-1.9) and ORadj 2.0 (95%CI 1.5-2.6); low birth weight (≤2499g) ORadj 1.6 (95%CI 1.3-2.1) and ORadj 2.1 (95%CI 1.6-2.8). Results of interpregnancy interval 12-17 months showed the same tendency – increased odds of preterm birth (ORadj 1,4 (95%CI 1.2-1.8) and low birth weight (ORadj 1.5 (95%CI 1.2-2.0). Increased odds of death in early antenatal period with shorter interpregnancy interval was observed but not statistically significant.Women with a primary education are much more likely to have a shorter interpregnancy intervals than women with a higher education. Mostly adverse pregnancy outcome is seen in women with interpregnancy interval ≤5 months and 6-11 months. These findings could be used for planning future pregnancies and giving guidance on family planning.