Background English Abortions have increased to over 185,000 pa in 2013. Woman undergoing a termination are often unaware of any subsequent risk to a future pregnancy or birth as it is not currently mentioned on the consent form. In Scandinavia, abortion registers have been kept and cohort studies undertaken to establish side-effects of terminations. This is not possible England. The NHS no. is not required to be recorded for this procedure, thus data cannot easily be linked and few studies have been undertaken in the UK to establish this risk. This study summarises results from international papers, in settings comparable to the NHS, published on this issue since 1990, and a meta-analysis has been conducted to quantify the risk.

Methods Data Sources, Searching and Eligibilty Criteria: Titles and Abstracts in Pubmed, Medline, Cochrane and DARE databases were searched. Jan 1990–Dec 2014 (all languages). Observational controlled studies were considered. Those which confused abortion and miscarriage were excluded. Medical and surgical abortions were distinguished where possible. Risk of bias was assessed using ACROBAT criteria and papers scored. Both reviewers collected data, and used the same eligibility criteria to abstract relevant studies independently. Expert authors were contacted for further data and hand searched references were reviewed.

Inclusions: 3828 titles were identified leading to 369 abstracts screened for eligibility and 16 studies met the inclusion criteria for the final meta-analysis using adjusted odds rations allowing for confounders (age, smoking, and other obstetric risk) for the summary adjusted odds ratio.

A meta-analysis was undertaken to measure the risk of preterm birth, including very preterm and extremely preterm birth after previous exposure to induced abortion, (medical and surgical distinguished) compared to mothers who had not had a termination

Results An increased risk of pre-term birth following a termination was observed in 15 studies. An overall adjusted Odds ratios (OR) of 1.16 for risk of preterm birth was observed after one or more abortions in 14 studies. A dose-response effect was seen after two or more abortions (11 studies) with greater risk of extreme premature delivery (below 28 weeks gestation) associated with 3 or more abortions (recorded in 3 studies).

Conclusion Women who have induced abortions are at increased risk of preterm birth in subsequent pregnancies. The risk is increased for extreme preterm birth with multiple abortions. This is an important public health issue and has implications for consent forms, research and commissioning in England.