Rates of recurrent preterm birth by obstetrical history and cervical length.

OBJECTIVE: This study was undertaken to determine rates of recurrent preterm birth according to number of prior preterm births, 1 versus 2 or more and cervical length by endovaginal ultrasound at 22(0) to 24(6) weeks, less than 25 mm versus more than 25 mm.

STUDY DESIGN: We retrospectively analyzed data from charts of women with prior spontaneous preterm birth seen in a Prematurity Prevention Clinic from 1998 through 2004. Women with a history of 1 or more spontaneous preterm births (18(0)-36(6) weeks) were included. Women with multiple gestations, uterine anomalies, and prior cervical surgery were excluded. Transvaginal sonography was used to evaluate each woman's cervical length at 22(0) to 24(6) weeks. Cerclage, bed rest, tocolysis, and steroids were used when clinically appropriate. Primary outcome was gestational age at delivery less than 32 and less than 35 weeks. Data were analyzed according to number of prior preterm births (1 vs > or = 2) and sonographic cervical length at 22(0) to 24(6) weeks (<25 mm vs > or = 25 mm).

RESULTS: A total of 188 eligible women were evaluated. Median gestational age of earliest preterm birth was 26.3 weeks. Of the total 188, 118 (62.8%) women had 1 prior and 70 (37.2%) had 2 or more preterm births. Thirty-eight (20.2%) of the women had a cervical length less than 25 mm and 150 (79.8%) had a cervical length 25 mm or greater. A higher percentage of women with a cervical length less than 25 mm and 2 or more preterm births delivered less than 32 weeks compared with women with 1 prior preterm birth, although this did not reach statistical significance (21.5% vs 12.5%, P = .47). Rates of delivery less than 35 weeks in women with a cervical length less than 25 mm were similar in those with a history of 1 and 2 or more preterm births. Women who had 2 or more prior preterm births were analyzed separately to identify if a cervical length greater than 30 mm or greater than 35 mm could be reassuring for decreasing the risk of recurrent preterm birth.

CONCLUSION: Rates of preterm birth less than 32 and less than 35 weeks were similar in women whose cervical length was less than 25 mm at 22(0) to 24(6) weeks, regardless of number of prior preterm births. Women with 2 prior preterm births and a cervix greater than 35 mm were at low risk for subsequent preterm birth less than 35 weeks.