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19: The impact of cervical length on risk of preterm birth in twin gestations

      Objective

      To compare rates of preterm birth(PTB) <35 weeks(wks) in women with twin gestations identified to have a short cervix defined as cervical length(CL) <25thpercentile(%ile) at 16-20 wks who received 17 alpha hydroxyprogesterone caproate(17OHPC) versus placebo.

      Study Design

      A secondary analysis of a randomized,double-blind,placebo-controlled trial of twin gestations exposed to 17OHPC versus placebo. Baseline transvaginal ultrasound of CL was performed prior to treatment assignment at 16-20 wks. The measurement cut off for 25th%ile was identified. Those with CL<25th and ≥25th%ile were compared regarding PTB <35 wks. The impact of 17OHPC in women with short cervix was evaluated.

      Results

      Of 661 twin gestations studied,221(33.4%) women underwent CL measurement. Of these,101 were randomized to 17OHPC; 120 received placebo.The 25th%ile CL at 16-20 wks was 36 mm(range 16-72 mm). Clinical characteristics such as race,gravidity,parity,pregravid BMI,prior PTB,chorionicity,assisted reproductive technology,gestational age at randomization were similar between groups. Women with CL ≥25th%ile were older than those with cervix <25th%ile(31±6.8 vs 29±6.5 years,p=0.046).The risk for PTB <35 wks was increased for women with short cervix after controlling for treatment(RR 1.5,95%CI 1.12, 2.14,see Table, *one lost to follow up). 17OHPC did not reduce PTB <35 wks among those with short or long cervix.
      Tabled 1
      TotalCervix < 25th %ileCervix ≥ 25th %ileP-value
      PTB <35wks29/52 (55.8%)62/168 (36.9%)0.016
      17OHPC43/101 (42.6%)18/28 (64.3%)25/73 (34.3%)0.006
      Placebo48/119 (40.3%)11/24 (45.8%)37/95 (39%)*0.53
      P-value0.740.180.53

      Conclusion

      In twin gestations, short CL at 16-20 wks is a marker for PTB. In the subgroup of women with twin gestation and CL <25th%ile, 17OHPC did not prevent PTB <35 wks.