• David M Haas, Taylor J Hathaway, and Patrick S Ramsey.
• Department of Obstetrics and Gynecology, Indiana University School of Medicine, 1001 West 10th Street, F-5, Indianapolis, Indiana, USA, 46202.
• Cochrane Db Syst Rev. 2018 Oct 8; 10: CD003511.

BackgroundProgesterone, a female sex hormone, is known to induce secretory changes in the lining of the uterus essential for successful implantation of a fertilized egg. It has been suggested that a causative factor in many cases of miscarriage may be inadequate secretion of progesterone. Therefore, clinicians use progestogens (drugs that interact with the progesterone receptors), beginning in the first trimester of pregnancy, in an attempt to prevent spontaneous miscarriage. This is an update of a review, last published in 2013.ObjectivesTo assess the efficacy and safety of progestogens as a preventative therapy against recurrent miscarriage.Search MethodsFor this update, we searched Cochrane Pregnancy and Childbirth's Trials Register, ClinicalTrials.gov, the WHO International Clinical Trials Registry Platform (ICTRP) (6 July 2017) and reference lists from relevant articles, attempting to contact trial authors where necessary, and contacted experts in the field for unpublished works.Selection CriteriaRandomized or quasi-randomized controlled trials comparing progestogens with placebo or no treatment given in an effort to prevent miscarriage.Data Collection And AnalysisTwo review authors independently assessed trials for inclusion and risk of bias, extracted data and checked them for accuracy. Two reviewers assessed the quality of the evidence using the GRADE approach.Main ResultsThirteen trials (2556 women) met the inclusion criteria. Nine of the included trials compared treatment with placebo and the remaining four trials compared progestogen administration with no treatment. The trials were a mix of multicenter and single-center trials, conducted in Egypt, India, Jordan, UK and USA. In six trials women had had three or more consecutive miscarriages and in seven trials women had suffered two or more consecutive miscarriages. Routes, dosage and duration of progestogen treatment varied across the trials. The majority of trials were at low risk of bias for most domains. Eleven trials (2359 women) contributed data to the analyses.The meta-analysis of all women, suggests that there is probably a reduction in the number of miscarriages for women given progestogen supplementation compared to placebo/controls (average risk ratio (RR) 0.69, 95% confidence interval (CI) 0.51 to 0.92, 11 trials, 2359 women, moderate-quality evidence). A subgroup analysis comparing placebo-controlled versus non-placebo-controlled trials and different routes of administration showed no differences between subgroups for miscarriage. However, there appears to be a subgroup difference for miscarriage between women with three or more prior miscarriages compared to women with two or more miscarriages, with a more pronounced effect in women with three or more prior miscarriages. However, it should be noted that there was high heterogeneity in the subgroup of women with three or more prior miscarriages.None of the trials reported on any secondary maternal outcomes, including severity of morning sickness, thromboembolic events, depression, admission to a special care unit, or subsequent fertility.There was probably a slight benefit for women receiving progestogen seen in the outcome of live birth rate (RR 1.11, 95% CI 1.00 to 1.24, 7 trials, 2086 women, moderate-quality evidence). While the rate of preterm birth is probably reduced for women receiving progestogen, this outcome was mainly driven by one trial and thus should be interpreted with great caution (RR 0.59, 95% CI 0.39 to 0.89, 5 trials, 811 women, moderate-quality evidence). No clear differences were seen for women receiving progestogen for the other secondary outcomes of neonatal death or fetal genital abnormalities. A possible reduction in stillbirth was seen, but again this outcome was driven mainly by one trial and should be interpreted with caution (RR 0.38, 95% CI 0.24 to 0.58, 3 trials, 1199 women). There may be little or no difference in the rate of low birthweight and trials did not report on the secondary child outcomes of teratogenic effects or admission to a special care unit.Authors' ConclusionsFor women with unexplained recurrent miscarriages, supplementation with progestogen therapy probably reduces the rate of miscarriage in subsequent pregnancies.

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