Interpregnancy interval following miscarriage and adverse pregnancy outcomes: systematic review and meta-analysis

BACKGROUND: A short interpregnancy interval (IPI) following a delivery is believed to be associated with adverse outcomes in the next pregnancy. The optimum IPI following miscarriage is controversial. Based on a single large-scale study in Latin and South America, the World Health Organization recommends delaying pregnancy for 6 months after a miscarriage to achieve optimal outcomes in the next pregnancy. OBJECTIVE AND RATIONALE: Our aim was to determine if a short IPI (<6 months) following miscarriage is associated with adverse outcomes in the next pregnancy. SEARCH METHODS: Studies were retrieved from MEDLINE, Embase and Pubmed, with no time and language restrictions. The search strategy used a combination of Medical Subject Headings terms for miscarriage, IPI and adverse outcomes. Bibliographies of the retrieved articles were also searched by hand. All studies including women with at least one miscarriage, comparing subsequent adverse pregnancy outcomes for IPIs of less than and more than 6 months were included. Two independent reviewers screened titles and abstracts for inclusion. Characteristics of the studies were extracted and quality assessed using Critical Appraisal Skills Programme criteria. A systematic review and meta-analysis were conducted to compare short (<6 months) versus long (>6 months) IPI following miscarriage in terms of risk of further miscarriage, preterm birth, stillbirth, pre-eclampsia and low birthweight babies in the subsequent pregnancy. Review Manager 5.3 was used for conducting meta-analyses. OUTCOMES: Sixteen studies including 1 043 840 women were included in the systematic review and data from 10 of these were included in one or more meta-analyses (977 972 women). With an IPI of less than 6 months, the overall risk of further miscarriage (Risk ratio (RR) 0.82 95% CI 0.78, 0.86) and preterm delivery (RR 0.79 95% CI 0.75, 0.83) were significantly reduced. The pooled risks of stillbirth (RR 0.88 95% CI 0.76, 1.02); low birthweight (RR 1.05 95% CI 0.48, 2.29) and pre-eclampsia (RR 0.95 95% CI 0.88, 1.02) were not affected by IPI. Similar findings were obtained in subgroup analyses when IPI of < 6 months was compared with IPI of 6-12 months and >12 months. WIDER IMPLICATIONS: This is the first systematic review and meta-analysis providing clear evidence that an IPI of less than 6 months following miscarriage is not associated with adverse outcomes in the next pregnancy. This information may be used to revise current guidance.