PREGNANCY INTERVAL

Registry study challenges recommended six-month pregnancy interval after miscarriage or abortion

Published 30 November 2022

Recommendations by the WHO that women should delay pregnancy by a least six months after a miscarriage or abortion might be unnecessarily cautious – or even mistaken - according to results of a large cohort study.(1) The study, involving almost 75,000 births, found that conception within three months of a miscarriage or abortion is not associated with increased risks of adverse pregnancy outcomes, and suggests that, contrary to current advice, women could attempt pregnancy without raised maternal or perinatal risks.(2) The results, say the authors, reassure those who want to try again sooner than the guidelines recommend.

The WHO has since 2007 advised that women should wait at least six months before trying to become pregnant again after a miscarriage or induced abortion. But this advice, say the study authors, has never been strong and is based largely on one study ‘likely to have resulted in substantial heterogeneity’. Since then, two cohort studies have failed to find any increased risk of adverse pregnancy outcomes in births following a short interpregnancy interval (<6 months) after a miscarriage, while a third did find a raised risk after induced abortion.

This latest study, performed in Australia, analysed 49,058 births following miscarriage and 23,707 following abortion recorded in the birth registries of Norway between 2008-2016. Six adverse outcomes were considered: preterm birth, spontaneous preterm birth, small for gestational age, large for gestational age, preeclampsia and gestational diabetes.

Results of the analysis showed that, when compared with waiting 6-11 months after miscarriage, there was a lower risks of small for gestational age for babies conceived in less than six months (RR 0.85), and a lower risk of gestational diabetes in women conceiving in under three months (RR 0.84). Similarly, following abortion there was a slight but non-significant increased risk of small for gestational age for conception in under three months, but the risk of large for gestational age was lower in the group with an interpregnancy interval of 3-5 months.

There was no evidence of higher risk of adverse pregnancy outcomes among women with an interpregnancy interval of greater than 12 months after miscarriages or induced abortions, with the exception of a modest increased risk of gestational diabetes. The authors acknowledge that the study was limited in that it lacked information on potential confounders, including pregnancy intention and ‘health seeking’ behaviour.

This may be evident in the authors’ explanation of why a short interpregnancy interval may not increase the risk of adverse outcomes in the next pregnancy. One possible explanation, they write, ‘would be that pregnancies conceived shortly after a miscarriage are more likely to be intended, and, hence, these women may seek health services with the aim of avoiding the previous unfavourable experience’.

However, the bottom line of the study is simply that women might attempt pregnancy soon after a previous miscarriage or induced abortion without increasing perinatal health risks. ‘Our results do not support current international recommendations to wait at least 6 months after miscarriages or induced abortions,’ they write, ‘and suggest a need to review these guidelines and provide up to date, evidence-based recommendations for women.’



1. World Health Organization. Report of a WHO technical consultation on birth spacing: Geneva, Switzerland 13–15 June 2005. World Health Organization; 2007. Available from: https://apps.who.int/iris/handle/10665/69855
2. Tessema GA, Håberg SE, Pereira G, et al. Interpregnancy interval and adverse pregnancy outcomes among pregnancies following miscarriages or induced abortions in Norway (2008–2016): A cohort study. PLoS Med 2022; 19(11): e1004129. https://doi.org/10.1371/journal.pmed.1004129

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