Prior uterine evacuation and risk for preterm birth

Abstract

We read with interest the meta-analysis by Saccone et al1Saccone G. Perriera L. Berghella V. Prior uterine evacuation of pregnancy as independent risk factor for preterm birth: a systematic review and metaanalysis.Am J Obstet Gynecol. 2016; 214: 572-591Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar 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. The vast majority of the reported odds ratios (OR) in this article were <2, most with a confidence interval (CI) approaching 1.0. Because of the large sample sizes, small differences in the outcomes can provide significant P values and narrow CI, which may yield statistically significant results but do not reflect meaningful clinical differences.2Grimes D.A. Schulz K.F. False alarms and pseudo-epidemics: the limitations of observational epidemiology.Obstet Gynecol. 2012; 120: 920-927Crossref PubMed Scopus (192) Google Scholar Additionally, we were surprised by the significantly higher OR provided by the Zhou et al3Zhou W. Sorensen H.T. Olsen J. Induced abortion and subsequent pregnancy duration.Obstet Gynecol. 1999; 94: 948-953Crossref PubMed Scopus (63) Google Scholar article in Figures 4, A; 5, A; 6, A; 10; and 12 (OR, 19.51; CI, 17.61–21.61) and were unable to verify those results in the original article. The authors suggest that perhaps women should be encouraged to use medical methods for uterine evacuation or to consider surgical methods with cervical preparation. We believe it is premature to make these recommendations because: (1) the overall association is weak; and (2) none of the studies included controlled for the variety of surgical techniques that may be used to evacuate a uterus, such as cervical preparation. Until we have more detailed information about the impact of various procedures and cervical preparation by gestational age, it is difficult to fully inform patients on the potential risk for preterm birth as a result of uterine evacuation. We would encourage the authors to reconsider their recommendations in light of the weak association between surgical uterine evacuation and subsequent preterm birth given that this is based on observational studies and the inherent limitations of this approach. Given the already hostile environment and stigma surrounding abortion care, we need to ensure that we avoid placing premature blame on surgical evacuation as a risk factor for preterm birth. Prior uterine evacuation of pregnancy as independent risk factor for preterm birth: a systematic review and metaanalysisAmerican Journal of Obstetrics & GynecologyVol. 214Issue 5PreviewPreterm 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. Full-Text PDF ReplyAmerican Journal of Obstetrics & GynecologyVol. 215Issue 6PreviewWe 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. Full-Text PDF