Medicine by the Numbers

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Preventing Spontaneous Abortion with Progestin Therapy


Am Fam Physician. 2019 Jul 1;100(1):online.


Details for This Review

Study Population: Women diagnosed with recurrent spontaneous abortion of unknown origin

Efficacy End Points: Spontaneous abortion, live birth, preterm labor

Harm End Points: None reported

Narrative: Spontaneous abortion, defined as loss of pregnancy before viability, is a common occurrence.1 A small percentage of women will experience three or more losses, a condition referred to as recurrent spontaneous abortion. The physical and emotional toll of recurrent spontaneous abortion can be high. Further, approximately only one-half of women who experience recurrent spontaneous abortion will discover the cause.2

When no cause is diagnosed for the recurrent losses, researchers and physicians postulate that low progesterone levels are the culprit.2 Progesterone plays a vital role in early pregnancy. It is secreted by the corpus luteum to induce changes in the lining of the uterus vital to implantation of the fetus. Theoretically, the administration of progestin or synthetic progesterone in early pregnancy will increase implantation rates and lead to more successful pregnancies. This review evaluates progestin as a therapy for women with recurrent pregnancy loss.3

The primary outcome in this review is spontaneous abortion and the analysis comes out in favor of treatment with progestin: a 26.3% spontaneous abortion rate in the control group and a 19.4% rate in the treatment group (number needed to treat [NNT] = 15; P = .0013). Studies varied in the method of administration of progestin, and no difference was shown between different routes. For the secondary end points that reached statistical significance, progestin therapy came out favorably. Patients saw decreased rates of preterm labor (NNT = 20; P = .012) as well as increased rates of live birth (NNT = 10; P = .042). Stillbirth rates were also decreased (NNT = 16; P < .00001).

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1 in 15 pregnant women did not have a spontaneous abortion

None reported

1 in 10 pregnant women went on to have a live birth

1 in 20 pregnant women

Author disclosure: No relevant financial affiliations.

Copyright © 2019 MD Aware, LLC ( Used with permission.

This series is coordinated by Dean A. Seehusen, MD, MPH, AFP Assistant Medical Editor, and Daniel Runde, MD, from the NNT Group.

A collection of Medicine by the Numbers published in AFP is available at


1. Salhi BA, Nagrani S. Acute complications of pregnancy. In: Walls R, Hockberger R, Gausche-Hill M, eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 9th ed. Philadelphia, Pa.: Elsevier; 2018:2237–2258.

2. Clinical overview: miscarriage and recurrent pregnancy loss. Elsevier Point of Care. ClinicalKey.!/content/clinical_overview/67-s2.0-8f91ecbf-e9f2-4579-97fa-54b72988d7cb. Accessed November 30, 2018.

3. Haas DM, Hathaway TJ, Ramsey PS. Progestogen for preventing miscarriage in women with recurrent miscarriage of unclear etiology. Cochrane Database Syst Rev. 2018;(10):CD003511.



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