A Population-Based Matched-Sibling Analysis Estimating the Associations Between First Interpregnancy Interval and...

Area of Science:

• Reproductive Health
• Perinatal Epidemiology
• Maternal-Fetal Medicine

Background:

• The interpregnancy interval (IPI) is the time between live birth and the next conception.
• Previous studies on IPI and birth outcomes have primarily used unmatched analyses.
• The impact of a single IPI on subsequent birth outcomes requires further investigation using robust methodologies.

Purpose of the Study:

• To investigate the association between interpregnancy interval (IPI) and adverse birth outcomes using matched sibling analyses.
• To specifically examine the odds of preterm birth, small for gestational age, and low birth weight in relation to IPI.

Main Methods:

• A cohort study of 192,041 sibling pairs born in Western Australia (1980-2010).
• Conditional logistic regression was used to model the interaction between birth order and IPI.
• The reference IPI category was 18-23 months.

Main Results:

• An interpregnancy interval (IPI) of less than 6 months was associated with significantly higher odds of preterm birth in the second-born infant (aOR=1.22, 95% CI: 1.06, 1.38).
• No significant associations were found for IPIs <6 months with small for gestational age or low birth weight.
• Matched analysis indicated a potentially smaller effect of short IPIs on preterm birth compared to unmatched studies.

Conclusions:

• This is the first study to employ matched analyses to assess the impact of a single interpregnancy interval on birth outcomes.
• Short interpregnancy intervals (<6 months) are associated with an increased risk of preterm birth in subsequent infants.
• The findings highlight the importance of considering sibling-matched designs for accurate estimation of IPI effects on perinatal health.