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

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Abstract
To determine what constitutes normal changes in the uterine cervix visible at transvaginal ultrasound examination from 24 gestational weeks until delivery in nulliparous women delivering at term. Cervical length and width were measured using transvaginal ultrasound, and the inner cervical os was assessed as being closed or open every 2 weeks from gestational week 24 until delivery in 19 healthy nulliparae delivering at term. 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), an accelerated shortening rate after approximately 30 gestational weeks (n = 5), or a sudden drop in length between the last two examinations (n = 3). The median rate of decrease in cervical length was 1 (range, 0.6–1.9) mm/week for women with continuous shortening of the cervix. For women with accelerated shortening the corresponding figure was 2.2 (range, 1.8–2.7) mm/week after the start of accelerated shortening. Two patterns of increase in cervical 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 women with continuous broadening of the cervix. For women with accelerated broadening rate the corresponding figure was 1.7 (range, 1.0–6.4) mm/week after 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 closing of the inner cervical os during examination) were seen in six women (32%) and were first detected at 31 gestational weeks. There are different patterns of normal change in cervical length 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. Copyright © 2001 International Society of Ultrasound in Obstetrics and Gynecology