Cervical length and maternal factors in expectantly managed prolonged pregnancy: prediction of onset of labor and mode of delivery.

OBJECTIVE To examine the value of combining cervical length and maternal characteristics in a prolonged-pregnancy clinic in the prediction of the probability of firstly, spontaneous onset of labor within the subsequent 10 days and secondly, the need for Cesarean section. METHODS This was a prospective study of women with singleton pregnancies attending an ultrasound-based prolonged-pregnancy clinic at 40 + 4 to 41 + 6 weeks of gestation. The policy was to delay induction of labor by 7-10 days unless there was evidence of a specific medical or obstetric indication or the mother wanted earlier delivery. The measurement of cervical length was not given to the obstetrician, midwife or patient. Regression analysis was used to determine which of the following factors had a significant contribution in predicting induction of labor: maternal age, body mass index (BMI), ethnic origin, parity and cervical length. Regression analysis was also used to determine which of the factors amongst the maternal characteristics, onset of labor and cervical length provided significant prediction of Cesarean section. RESULTS We examined 2316 pregnancies but we excluded from further analysis 452 (19.5%) cases because iatrogenic delivery was carried out within the subsequent 6 days, including 427 cases of induction of labor (340 at the request of the mother and 87 for medical indications) and 25 cases of Cesarean section. In the remaining 1864 cases there was spontaneous onset of labor and delivery within 10 days in 1536 (82.4%) and induction of labor in 7-10 days in 328 (17.6%). The rate of Cesarean section was 15.2% (233 of 1536) in those with spontaneous onset of labor and 36.0% (118 of 328) in those whose labor was induced. Regression analysis demonstrated that in the prediction of induction of labor there were significant contributions from cervical length, BMI, parity and gestational age, and in the prediction of Cesarean section there were significant contributions from onset of labor, cervical length, BMI, parity and ethnicity. CONCLUSION Ultrasonographic measurement of cervical length at 41 weeks together with maternal factors can define the patient-specific probability of spontaneous onset of labor in the subsequent week and the risk of Cesarean section.