Association of Short Interpregnancy Interval With Pregnancy Outcomes According to Maternal Age

Abstract

IMPORTANCE Interpregnancy intervals shorter than 18 months are associated with higher risks of adverse pregnancy outcomes. It is currently unknown whether short intervals are associated with increased risks among older women to the same extent as among younger women. OBJECTIVE To evaluate whether the association between short interpregnancy (delivery to conception) interval and adverse pregnancy outcomes is modified by maternal age. DESIGN, SETTING, AND PARTICIPANTS A population-based cohort study conducted in British Columbia, Canada, evaluated women with 2 or more singleton pregnancies from 2004 to 2014 with the first (index) pregnancy resulting in a live birth. Data analysis was performed from January 1 to July 20, 2018. MAIN OUTCOMES AND MEASURES Risks of maternal mortality or severe morbidity (eg, mechanical ventilation, blood transfusion >3 U, intensive care unit admission, organ failure, death), small-for-gestational age (<10th birthweight percentile for gestational age and sex), fetal and infant composite outcome (stillbirth, infant death, <third birthweight percentile for gestational age and sex, delivery <28 weeks), and spontaneous and indicated preterm delivery. Risks of each outcome for 3-to 24-month interpregnancy intervals were estimated, according to maternal age at index birth (20-34 and Ն35 years). Adjusted risk ratios (aRRs) comparing predicted risks at 3-, 6-, 9-, and 12-month intervals with risks at 18-month intervals for each age group were calculated. The potential role of other factors explaining any differences (unmeasured confounding) was examined in several sensitivity analyses. RESULTS Among 148 544 pregnancies, maternal mortality or severe morbidity risks were increased at 6-month compared with 18-month interpregnancy intervals for women aged 35 years or older (0.62% at 6 months vs 0.26% at 18 months; aRR, 2.39; 95% CI, 2.03-2.80), but not for women aged 20 to 34 years (0.23% at 6 months vs 0.25% at 18 months; aRR, 0.92; 95% CI, 0.83-1.02). Increased adverse fetal and infant outcome risks were more pronounced for women aged 20 to 34 years (2.0% at 6 months vs 1.4% at 18 months; aRR, 1.42; 95% CI, 1.36-1.47) than women 35 years or older (2.1% at 6 months vs 1.8% at 18 months; aRR, 1.15; 95% CI, 1.01-1.31). Risks of spontaneous preterm delivery at 6-month interpregnancy intervals were increased for women 20 to 34 years old (5.3% at 6 months vs 3.2% at 18 months; aRR, 1.65; 95% CI, 1.62-1.68) and to a lesser extent for women 35 years or older (5.0% at 6 months vs 3.6% at 18 months; aRR, 1.40; 95% CI, 1.31-1.49). Modest increases in risks of small-for-gestational age and indicated preterm delivery at short intervals did not vary meaningfully by maternal age. Sensitivity analyses suggested that observed associations were not fully explained by unmeasured confounding. CONCLUSIONS AND RELEVANCE The findings of this study suggest that short interpregnancy intervals are associated with increased risks for adverse pregnancy outcomes for women of all ages.

Interpregnancy intervals and women’s knowledge of the ideal timing between birth and conception

“…These observations led to current clinical and public health recommendations advising a minimum IPI of 18 months 9. More recent studies that have matched women as their own controls, to reduce confounding factors, have identified that an IPI <12 months confers greater risk for preterm birth and small for gestational age in high-resource settings, which supports the findings from the previous studies 3 10 11…”

Contraception after pregnancy

“…In a study of women giving birth in Sweden, short interpregnancy intervals (0‐3 months) were not causally associated with increased risk of stillbirth or early neonatal death . A study from British Columbia confirmed the lack of association for women under 35 years but cautioned against short interpregnancy intervals for older women . In low‐ and middle‐income countries where maternal and perinatal mortality and morbidity are high and where women may often start, and end, a pregnancy undernourished and anemic, long interpregnancy intervals may be beneficial.…”

Association between interpregnancy interval and subsequent stillbirth in 58 low-income and middle-income countries: a retrospective analysis using Demographic and Health Surveys

“…5 There is little research on modifying interpregnancy inter vals; possible strategies to change such intervals could include educational programmes, cash transfer programmes, and contraception provision programmes, which have been shown to reduce pregnancy rates in LMICs. 6,7 Several studies have examined the association between interpregnancy interval and subsequent adverse perinatal and maternal outcomes, such as small-for-gestationalage birth, 8 preterm birth, 9 low birthweight, 10 child mortality, 11,12 maternal death, 13 and, to a lesser extent, stillbirth. 14 Although many of these studies have found strong associations between short interpregnancy intervals and adverse birth outcomes, there is ongoing debate regarding whether or not the relationship is causal.…”