The aim of our study is to evaluate the effect of use of prophylactic vaginal progesterone on the incidence of severe preterm delivery, defined as delivery before 33+6 weeks in women with a short cervical length of 15mm.

BACKGROUND The results of randomized studies have shown that the prophylactic use of progesterone in women who previously delivered prematurely reduces the risk of recurrence. Asymptomatic women found to have a short cervix (< 15 mm) at mid-gestation are at greatly increased risk for spontaneous early preterm delivery and it is uncertain whether in such women the risk is reduced by progesterone.

METHODS Cervical length was measured by transvaginal sonography at 22 (range 20-25) weeks in 24,620 pregnant women attending for routine antenatal care. The cervix was 15 mm or less in 413 (1.7%), and 250 (60.5%) of these women participated in a randomized study of vaginal progesterone (200 mg per night) vs identical-looking placebo, between 24 and 34 weeks. Primary outcome was the frequency of spontaneous delivery before 34 weeks (238 days) of pregnancy. Analysis was performed according to the intention-to-treat principle.

Inclusion Criteria:

• All women with singleton or twin pregnancies attending for routine ultrasound examination at 20-25 weeks of gestation with a short cervical length (<15 mm).

Exclusion Criteria:

• Women with major fetal abnormalities,
• Painful regular uterine contractions, or history of ruptured membranes or cervical cerclage in-situ were excluded from screening.