Relationship Between Interpregnancy Interval and Adverse Perinatal and Neonatal Outcomes in Northern Alberta

Birth outcomes are known to be associated with birth spacing, but there are population differences. The purpose of this study was to examine the association between interpregnancy intervals and perinatal and neonatal outcomes in a Canadian population during the era of mandatory folate fortification of food.

We conducted a study of 46 243 women who had two consecutive singleton births in northern Alberta between 1999 and 2007, using a linked provincial dataset. Perinatal outcomes of interest were preterm birth, low birth weight (LBW), small for gestational age, and perinatal death. Neonatal outcomes were low Apgar score, low arterial blood gas pH, need for neonatal resuscitation or admission to NICU, and neonatal death. Multivariable logistic regression was used to control for maternal demographic and obstetrical characteristics.

The risk of preterm birth was increased for multiple interpregnancy intervals: for an interval of 0 to 5 months, the adjusted odds ratio (aOR) was 1.37 (95% CI 1.18 to 1.59), for 6 to 11 months the aOR was 1.18 (95% CI 1.04 to 1.34), for 24 to 35 months the aOR was 1.16 (95% CI 1.02 to 1.31), and for 36+ months the aOR was 1.36 (95% CI 1.20 to 1.53), compared with the reference interval of 12 to 17 months. The risk of LBW was increased with interpregnancy intervals of 0 to 5 months (aOR 1.48; 95% CI 1.23 to 1.80), 6 to 11 months (aOR 1.21; 95% CI 1.03 to 1.42), 24 to 35 months (aOR 1.21; 95% CI 1.03 to 1.41) and 36+ months (aOR 1.48; 95% CI 1.27 to 1.73). The risk of SGA was increased with intervals 0 to 5 months (aOR 1.29; 95% CI 1.09 to 1.52), 24 to 35 months (aOR 1.15; 95% CI 1.01 to 1.31), and 36+ months (aOR 1.26; 95% CI 1.11 to 1.44). The risk of perinatal death was increased with an interval of 36+ months (aOR 1.60; 95% CI 1.06 to 2.43). Similar associations were also observed for neonatal outcomes.

This study suggests that both short and long interpregnancy intervals are associated with adverse perinatal and neonatal outcomes, and it provides risk estimates for a Canadian population in the era of folate fortification of food.