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Prior uterine evacuation of pregnancy as independent risk factor for preterm birth: a systematic review and metaanalysis

Published:December 29, 2015DOI:https://doi.org/10.1016/j.ajog.2015.12.044

      Background

      Preterm birth (PTB) is the number one cause of perinatal mortality. Prior surgery on the cervix is associated with an increased risk of PTB. History of uterine evacuation, by either induced termination of pregnancy (I-TOP) or spontaneous abortion (SAB), which involve mechanical and/or osmotic dilatation of the cervix, has been associated with an increased risk of PTB in some studies but not in others.

      Objective

      The objective of the study was to evaluate the risk of PTB among women with a history of uterine evacuation for I-TOP or SAB.

      Data Sources

      Electronic databases (MEDLINE, Scopus, ClinicalTrials.gov, EMBASE, and Sciencedirect) were searched from their inception until January 2015 with no limit for language.

      Study Eligibility Criteria

      We included all studies of women with prior uterine evacuation for either I-TOP or SAB, compared with a control group without a history of uterine evacuation, which reported data about the subsequent pregnancy.

      Study Appraisal and Synthesis Methods

      The primary outcome was the incidence of PTB < 37 weeks. Secondary outcomes were incidence of low birthweight (LBW) and small for gestational age (SGA). We planned to assess the primary and the secondary outcomes in the overall population as well as in studies on I-TOP and SAB separately. The pooled results were reported as odds ratio (OR) with 95% confidence interval (CI).

      Results

      We included 36 studies in this metaanalysis (1,047,683 women). Thirty-one studies reported data about prior uterine evacuation for I-TOP, whereas 5 studies reported data for SAB. In the overall population, women with a history of uterine evacuation for either I-TOP or SAB had a significantly higher risk of PTB (5.7% vs 5.0%; OR, 1.44, 95% CI, 1.09–1.90), LBW (7.3% vs 5.9%; OR, 1.41, 95% CI, 1.22–1.62), and SGA (10.2% vs 9.0%; OR, 1.19, 95% CI, 1.01–1.42) compared with controls. Of the 31 studies on I-TOP, 28 included 913,297 women with a history of surgical I-TOP, whereas 3 included 10,253 women with a prior medical I-TOP. Women with a prior surgical I-TOP had a significantly higher risk of PTB (5.4% vs 4.4%; OR, 1.52, 95% CI, 1.08–2.16), LBW (7.3% vs 5.9%; OR, 1.41, 95% CI, 1.22–1.62), and SGA (10.2% vs 9.0%; OR, 1.19, 95% CI, 1.01–1.42) compared with controls. Women with a prior medical I-TOP had a similar risk of PTB compared with those who did not have a history of I-TOP (28.2% vs 29.5%; OR, 1.50, 95% CI, 1.00–2.25). Five studies, including 124,133 women, reported data about a subsequent pregnancy in women with a prior SAB. In all of the included studies, the SAB was surgically managed. Women with a prior surgical SAB had a higher risk of PTB compared with those who did not have a history of SAB (9.4% vs 8.6%; OR, 1.19, 95% CI, 1.03–1.37).

      Conclusion

      Prior surgical uterine evacuation for either I-TOP or SAB is an independent risk factor for PTB. These data warrant caution in the use of surgical uterine evacuation and should encourage safer surgical techniques as well as medical methods.

      Key words

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      Linked Article

      • Prior uterine evacuation and risk for preterm birth
        American Journal of Obstetrics & GynecologyVol. 215Issue 6
        • Preview
          We read with interest the meta-analysis by Saccone et al1 regarding the risk of preterm birth in women with a history of uterine evacuation. While the authors used rigorous methodology to conduct their meta-analysis, the outcomes are only as good as the original data from which they are derived. Since most of the original studies did not include a number of known confounders for preterm birth, including prior preterm birth, multiple gestations, and short interpregnancy interval to name a few, it is important to highlight the potential for bias and false assumptions based on the meta-analysis.
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      • Re: Prior uterine evacuation of pregnancy as independent risk factor for preterm birth: a systematic review and metaanalysis
        American Journal of Obstetrics & GynecologyVol. 216Issue 1
        • Preview
          The meta-analysis by Dr Saccone and colleagues1 concludes that surgical abortion “is an independent risk factor” for subsequent preterm birth. The authors found a weak association (odds ratios [OR], 1.44; 95% confidence interval, 1.09–1.90) between abortion and preterm birth, but we question whether this association is causal. We agree with the discussion of study limitations and will highlight several key points. First, the reported associations all had OR <2. Not only do bias and confounding often account for weak associations, but OR exaggerate true relative risk.
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      • Reply
        American Journal of Obstetrics & GynecologyVol. 215Issue 6
        • Preview
          We thank Dr Quinn et al for their interest in our study.1 Their letter offers a possible explanation for why women with prior abortion have an increased risk of spontaneous preterm delivery. They speculate that both surgical and medical evacuation of the uterus might result in injuries of the uterosacral ligaments and of the uterovaginal nerves, which could lead to an increased risk of preterm labor. They also state that “medical evacuation complicated by excessive uterine activity may increase the risk of preterm labor.” These statements raise at least 3 issues.
        • Full-Text
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      • Medical evacuation of the uterus and subsequent preterm labor
        American Journal of Obstetrics & GynecologyVol. 215Issue 6
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          Several systematic reviews draw attention to a relationship between medical or surgical evacuation of the uterus and subsequent preterm labor though do not suggest potential mechanisms. Saccone et al1 conclude that “Prior surgical uterine evacuation for either induced termination of pregnancy or spontaneous abortion is an independent risk factor for preterm birth. These data warrant caution in the use of surgical uterine evacuation and should encourage safer surgical techniques as well as medical methods.”
        • Full-Text
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      • Reply
        American Journal of Obstetrics & GynecologyVol. 215Issue 6
        • Preview
          We thank Macafee et al for their interest in our study.1 They emphasize important issues, with which we in general agree. In our manuscript we highlighted the limitations of the meta-analysis, including that about half of the original studies did not adjust for confounders, and because of the stigma associated with abortion, previous procedures may have been underreported in the case and control groups. Lack of adjustment for confounders is indeed an important limitation. Approximately 18 of the 36 included studies (references 24−27, 29−35, 37−39, 44−47) did adjust for some confounders, and most found an association with surgical termination and preterm birth, even after they adjusted for confounders.
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      • Reply
        American Journal of Obstetrics & GynecologyVol. 216Issue 1
        • Preview
          We thank Dr Averbach et al for their interest in our study. As we have highlighted in our article1 and in prior letters,2,3 we completely agree that we have found a weak association (odds ratio <2) between abortion and preterm birth and acknowledge the high risk of bias of the included studies. Most of the included studies did not control appropriately for confounders, and only 6 included parity, an important determinant of preterm delivery,4 as a potential confounder. Moreover, because women face stigma when reporting an induced abortion, patients in the case or control group could have omitted abortion from their medical history, which would lead to a high risk of recall bias.
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