Mothers should wait at least a year between giving birth and getting pregnancy again to reduce health risks to mother and baby, a large study says. But researchers say they need not wait as long as the 18 months recommended in the current World Health Organisation guidelines.
Small gaps between pregnancies risk premature births, smaller babies and infant and mother mortality.
The researchers hope the findings will be “reassuring” for older women. Senior study author Dr Wendy Norman said in the report that it was “encouraging news” for women over 35 who were planning their families. “Older mothers for the first time have excellent evidence to guide the spacing of their children,” she said. “Achieving that optimal one-year interval should be doable for many women and is clearly worthwhile to reduce complication risks.”
The report says the study, of nearly 150,000 births in Canada undertaken by researchers at the University of British Columbia (UBC) and the Harvard TH Chan School of Public Health, found 12-to-18 months was the ideal length of time between giving birth and becoming pregnant again. Current World Health Organisation guidelines recommend an ideal interval of 24 months and no fewer than 18 months.
The researchers also found: getting pregnant less than 12 months after giving birth was associated with risks for women for all ages; there were risks to the mother only for women over the age of 35, while risks to the infant were found for all women, but were greatest for those aged between 20 and 34; women over 35 who conceived six months after a previous birth had a 1.2% risk of maternal mortality or harm (12 cases per 1,000 pregnancies); waiting 18 months between pregnancies reduced the risk to 0.5% (five cases per 1,000); and younger women who got pregnant six months after a previous birth had an 8.5% risk of premature labour – this dropped to 3.7% if they waited 18 months between pregnancies
The study’s lead author, Laura Schummers, said: “Our study found increased risks to both mother and infant when pregnancies are closely spaced, including for women older than 35. “The findings for older women are particularly important, as older women tend to more closely space their pregnancies and often do so intentionally.”
The report says the study looked at only one population of women – in Canada – so it is unclear how applicable this would be worldwide. Researcher Dr Sonia Hernandez-Diaz said the findings suggested different risks for each age group. “Short pregnancy spacing might reflect unplanned pregnancies, particularly among young women.
“Whether the elevated risks are due to our bodies not having time to recover if we conceive soon after delivering or to factors associated with unplanned pregnancies, like inadequate prenatal care, the recommendation might be the same: improve access to postpartum contraception, or abstain from unprotected sexual intercourse with a male partner following a birth.”
Mandy Forrester, from the Royal College of Midwives, said the study was “useful research and builds on previous research into birth spacing”. “Ultimately, it will be a woman’s choice, whatever age they are, about how long they leave between their pregnancies. What is important is that they are aware of the evidence around birth spacing and that they make their choice armed with the right information.
“Health professionals will always support a woman in her choice, which will be about what is right for them and their pregnancy.
She said women needed access to contraceptive advice to allow them to space their births, if that was their choice, but said in specialist family planning service provision in the UK was “patchy, with GPs frequently offering only oral contraception”.
“Specialist services should be available for all women.”
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, 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.
Laura Schummers; Jennifer A Hutcheon; Sonia Hernandez-Diaz; Paige L Williams; Michele R Hacker; Tyler J VanderWeele; Wendy V Norman