Background Premature births have increased in the UK in the last decade. The incidence of PTB in Scotland is now at an all-time high. The cause remains a mystery. We aim to quantify the risk of moderate PTB (mPTB<37 weeks), very PTB (vPTB<32 weeks) and extremely PTB (xPTB<28 weeks) allowing for other risk factors, following single and multiple abortions, and single and multiple miscarriages using a series of systematic meta-analysis of papers published 1990–2019.
Methods Systematic review* using PubMed, Cochrane, and Embase of papers published 1990–2019 and meta-analyses of observational studies were conducted separately for ToP and miscarriage. 67 separate studies were identified from 22 eligible papers for ToP; Further investigation allowed analysis relating to numbers of ToP, numbers of miscarriages and the degree of prematurity according to gestational birth age. Bias and Heterogeneity are measured and considered.
Results Miscarriage: AdjOR between 1.70, 95% CI (1.51–1.92) from Denmark and 1.12 (1.08–1.16) from Scotland for PTB after one miscarriage were noted from papers. These risks increased after two miscarriages with adjOR of between 2.20 (0.70–2.0) from Seattle and 1.36 (1.25–1.47) from Scottish data; AdjOR for xPTB after two or more miscarriages were between 4.0 (2.3–7.1) from Sweden and 2.81 (1.47–5.38) from Scotland. Iran reported Adj OR for xPTB of 4.10 (2.08–8.08) after three+ miscarriages.
Abortion and Meta-analysis: Fifty of the 67 studies demonstrated a significant increased risk of PTB related to abortion. Data was obtained from 22 countries worldwide. Risk of PTB after one+ abortion carried an Adj OR of 1.52 95% CI (1.43–1.62) compared to matched women who had no ToP (67 studies); Risk for corresponding miscarriage was 1.31 (1.18–1.45). Risk of vPTB after either ToP or miscarriage increased with increasing numbers of both ToP and miscarriage. The greatest risk increase noted was for xPTB after three+ ToP with Adj OR of 5.22 (1.58–17.21), whilst for three+ miscarriages it was 3.87 (2.85–5.26).
Risk of PTB was also measured according to method of abortion, or miscarriage treatment, and Adj OR compared for medical versus surgical treatments.
Conclusion The likelihood of xPTB increased after multiple Top (3 or more) and increased for miscarriages but to a lesser degree. The risk of any PTB also increases with multiple ToP and with several miscarriages. This is an important public health finding for women’s choices for consent to ToP or to treatment after miscarriage in the UK. It has implications for costs, future research and reduction of premature births in the UK.
* Included studies 6005 titles and abstracts were identified 1990–2019 and papers were screened for eligibility. 43 papers were selected for systematic review, from which 23 papers (with 3,796,010 participants) met the inclusion criteria for the meta–analysis for ToP.
Papers which did not distinguish miscarriage from abortion, and studies with overlapping data were excluded.
The search strategy used MESH terms for Abortion or ToP ((‘Abortion, Induced’ or ‘Abortion, Legal’ or ‘Abortion, Therapeutic’, ‘Termination of pregnancy’ ) AND (‘’infant, premature’ ’or ‘obstetric labor, premature’ or ‘premature birth’ or ‘preterm birth’ ‘fetal membranes, premature rupture’ or ‘’Pregnancy complications, or ‘pregnancy outcome’.
For Miscarriage: (‘miscarriage’; ‘spontaneous abortion’; ‘pregnancy loss’)’
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