Background: Prolonged pregnancy occurs in approximately 10% of all singletone pregnancy and is associated with an increased risk of foetal macrosomia, intrapartum fetal cardiac abnormalities, meconium staining, perinatal death, and cesarean delivery. Objective: To detect the relationship between transvaginal ultrasound measurement of cervical length at 37 weeks of pregnancy and prolonged pregnancy in nullipara. Patients and Methods: This was a prospective study of women attending Mataria teaching hospital was conducted from January 2019 to December 2019. The study included 120 women at 37 weeks of gestation observed till time of delivery. Gestational age was determined from the menstrual history and confirmed by an ultrasound scan and measurement of the crown–rump length in the first trimester, or the head circumference in the second trimester. Results: This study showed that cervical length at weeks can predict the likelihood of prolonged pregnancy and is associated with the gestation at spontaneous onset of labor in low-risk nulliparous women and the best cut-off value for prediction of prolonged pregnancy was 3.3cm with a sensitivity of 80% and specificity of 83.1. Conclusions: Transvaginal ultrasound measurement of cervical length at 37 weeks of pregnancy is important for prediction of the duration of pregnancy in primigravidae.