Interpregnancy interval and adverse perinatal outcomes: A within-individual comparative method.

Area of Science:

• Reproductive Epidemiology
• Maternal-Fetal Medicine
• Perinatal Health

Background:

• Previous studies on interpregnancy interval (IPI) and perinatal outcomes used between-individual methods, potentially confounded by unmeasured maternal factors.
• This study employed within-individual analyses to provide a more robust examination of the IPI-perinatal outcome association.

Purpose of the Study:

• To investigate the association between interpregnancy interval (IPI) and adverse perinatal outcomes using within-individual comparative analyses.
• To mitigate confounding from unmeasured, time-invariant maternal characteristics.

Main Methods:

• Utilized data from 10,647 individuals with at least three liveborn singleton pregnancies from the NICHD Consecutive Pregnancies Study.
• Employed conditional logistic regression, matching two IPIs per individual and adjusting for within-individual factors.
• Examined outcomes including preterm birth (PTB), small-for-gestational-age (SGA), low birthweight (LBW), and NICU admission.

Main Results:

• No significant increase in odds for PTB, SGA, LBW, or NICU admission was observed for IPIs <6 months compared to the 18-23 month reference interval.
• IPIs of 6-11 months and 12-18 months also showed no clear association with increased odds of adverse outcomes.
• An interpregnancy interval of ≥24 months was associated with increased odds of delivering a low birthweight infant.

Conclusions:

• Within-individual analyses did not support an association between short interpregnancy intervals (<6 months) and increased odds of adverse perinatal outcomes.
• Longer interpregnancy intervals (≥24 months) were associated with a higher likelihood of low birthweight.
• The findings highlight the importance of considering the directionality of IPI effects on specific perinatal outcomes.