Patterns of normal change in cervical length and width during pregnancy innulliparous women: a prospective, longitudinal ultrasound study

Objectives To determine what constitutes normal changes in the uterine cerv ix visible at transvaginal ultrasound examination from 24 gestational weeks until delivery in nulliparous women delivering at term. Design Cervical length and width were measured using transvaginal ultrasoun d, and the inner cervical os was assessed as being closed or open every 2 w eeks from gestational week. 24 until delivery in 19 healthy nulliparae deli vering at term. Results In all but one woman cervical length decreased, and in all but one woman cervical width increased, with advancing gestation. Three Patterns of change in cervical length were observed: a continuous decrease (n = 10), a n accelerated shortening rate after approximately 30 gestational weeks (n = 5), ora sudden drop in length between the last two examinations (n = 3). T he median rate of decrease in cervical length was 1 (range, 0.6-1.9) mm/wee k for women with continuous shortening of the cervix. For women with accele rated shortening the corresponding figure was 2.2 (range, 1.82.7) mm/week a fter the start of accelerated shortening. Two patterns of increase in cervi cal width (cervical broadening) were noted: a continuous increase (n = 12), or an accelerated broadening rate from around 32 weeks (n = 6). The median rate of increase in cervical width was 0.8 (range, 0.3-2.0) mm/week for wo men with continuous broadening of the cervix. For women with accelerated br oadening rate the corresponding figure was 1.7 (range, 1.0-6.4) mm/week aft er the start of increased broadening rate. Opening of the internal cervical os was observed at least once in eight of the 19 women (42%) and was first observed at 30 gestational weeks. Dynamic changes (i.e. opening and closin g of the inner cervical os during examination) were seen in six women (32%) and were first detected at 31 gestational weeks. Conclusions There are different patterns of normal change in cervical lengt h and width during pregnancy in nulliparous women. This must be taken into account if repeated ultrasound examinations of the cervix during pregnancy are used to identify nulliparae at increased risk of preterm delivery.