In a multivariable logistic regression model, independent risk factors for non-response to 17-OHPC were each additional week of gestation of the earliest previous preterm birth (odds ratio [OR], 1.23; 95 % CI: 1.17 to 1.30, p < 0.001), placental abruption or significant vaginal bleeding (OR, 5.60; 95 % CI: 2.46 to 12.71, p < 0.001), gonorrhea and/or chlamydia in the current pregnancy (OR, 3.59; 95 % CI: 1.36 to 9.48, p = 0.010), carriage of a male fetus (OR, 1.51; 95 % CI: 1.02 to 2.24, p = 0.040), and a penultimate preterm birth (OR, 2.10; 95 % CI: 1.03 to 4.25, p = 0.041). Cervical length was 15 mm or less in 413 of the women (1.7 %), and 250 (60.5 %) of these 413 women were randomly assigned to receive vaginal progesterone (200 mg each night) or placebo from 24 to 34 weeks of gestation. Intra-uterine Device (IUD) What is it? The primary study outcome was delivery or fetal death before 35 weeks of gestation. The size of the Kyleena T-body is 28mm x 30mm, and its placement tube has a diameter of 3.8mm. Summary of randomized studies indicates that in women with singleton gestations, no prior PTB, and short CL less than or equal to 20 mm at less than or equal to 24 weeks, vaginal progesterone, either 90-mg gel or 200-mg suppository, is associated with reduction in PTB and perinatal morbidity and mortality, and can be offered in these cases. It is placed inside the womb by a healthcare provider. The mean gestational age at delivery was 35.4 weeks for the 17α-hydroxyprogesterone caproate group and 35.7 weeks for the placebo group (p = 0.32).

A meta-analysis was performed on randomized trials including singleton pregnancies with previous preterm birth.

The primary outcome was delivery or intra-uterine death before 34 weeks' gestation. Additionally, as an intramuscular injection administered every 3 months, Depo-Provera has been shown to be highly effective in the prevention of pregnancy (less than 1 % failure rate in the first year).

Spontaneous delivery before 34 weeks of gestation was less frequent in the progesterone group than in the placebo group (19.2 % versus 34.4 %; relative risk, 0.56; 95 % CI: 0.36 to 0.86). These investigators used decision-analytic and cost-effectiveness analyses to estimate which of 4 strategies was superior based on quality-adjusted life-years, cost in US dollars, and number of preterm births prevented. 17-OHPC with that of vaginal progesterone for prevention of recurrent preterm birth. The overall impact on US natality was real but modest: 2% (12.1% - 11.8%) and suggested 17P appears to be more valuable in reducing preterm birth in eligible women than the general population.There is a limited overall effect in general population. In these women with prior PTB, if the trans-vaginal ultrasound CL shortens to less than 25 mm at less than 24 weeks, cervical cerclage may be offered. The authors concluded that administration of vaginal progesterone gel to women with a sonographic short cervix in the mid-trimester is associated with a 45 % reduction in the rate of preterm birth before 33 weeks of gestation and with improved neonatal outcome.Klein and colleagues (2011) noted that progesterone treatment reduces the risk of preterm delivery in high-risk singleton pregnancies.

The primary outcome was birth before 37 weeks of pregnancy. Women who received vaginal progesterone had a significantly lower rate of SPTB less than 34 weeks (17.5 % versus 25.0 %; RR 0.71, 95 % CI: 0.53 to 0.95; low quality of evidence) and SPTB less than 32 weeks (8.9 % versus 14.5 %; RR 0.62, 95 % CI: 0.40 to 0.94; low quality of evidence) compared to women who received 17-OHPC. Three studies pertained to 1st-generation endometrial ablation (manual hysteroscopy) and 3 to 2nd-generation endometrial ablation (thermal balloon). The least common pattern was frequent bleeding, defined as more than 5 episodes of bleeding in a reference period. In high doses, progestins are relatively effective in suppression of menstrual cycling in girls and women and androgen levels in boys and men. Nonetheless, implementation of such a screening strategy can be viewed as reasonable, and can be considered by individual practitioners, following strict guidelines. The authors concluded that 17α-hydroxyprogesterone caproate does not prevent neonatal morbidity or preterm birth in multiple pregnancies.Rode et al (2009) provided an update on the preventive effect of progesterone on preterm birth in singleton pregnancies. The most common bleeding pattern observed throughout the study was infrequent bleeding, defined as less than 3 episodes of bleeding in a reference period (excluding amenorrhea). Searches were performed in electronic databases. Three participants in each group were lost to follow-up, leaving 247 analysed per group. Baseline characteristics for progesterone and placebo groups were similar.