Objective: To identify the risk factors for preterm birth in primigravidae with twin gestation and the role of transvaginal ultrasonographic assessment of the cervix.
Methods: Between January 1996 and December 1996, 54 twin pregnancies were prospectively enrolled. All women were at their first pregnancy. All women conceived following infertility treatments and all had a normal uterine cavity proven by hysterosalpingography (HSG) or hysteroscopy. Multiple logistic regression analysis was used to evaluate the association between the length of the cervix at 18-24 weeks of gestation and outcome variables, controlling for possible confounding factors.
Results: The mean +/- SD maternal age was 30.9 +/- 5.3 years (range 22-46), and five of them were aged 40 or more. Nine patients (20.5%) delivered prematurely, defined as spontaneous delivery at or before 34 weeks of gestation. There was no statistically significant difference between women who delivered before or after 34 weeks of gestation in regard to maternal age, body mass index (BMI), weight gain in pregnancy, smoking and work during pregnancy. The mean cervical length of patients who delivered before 34 weeks of gestation (30.1 +/- 6.1 mm) was significantly shorter than that of women who delivered after 34 weeks of gestation (42.2 +/- 6.2 mm; P < 0.001). Cervical length longer than 35 mm predicted delivery after 34 weeks of gestation with sensitivity and specificity of 88.5% and 88.9%, respectively. The positive and negative predictive values were 96.9% and 66.7%.
Conclusion: A transvaginal ultrasonographic measurement of the cervix > 35 mm at 18-24 weeks in twin gestation can identify patients at low risk for delivery before 34 weeks. Maternal age, BMI, weights gain, smoking and work during the pregnancy did not influence the duration of the pregnancy.