Cervical length at 23 weeks of gestation: relation to demographic characteristics and previous obstetric history.

OBJECTIVES To examine the feasibility of introducing routine measurement of cervical length at 23 weeks of gestation, to establish the distribution of cervical lengths in a routine population of singleton pregnancies and to examine the relation between cervical length and demographic characteristics and previous obstetric history. METHODS Cervical length was measured by transvaginal sonography at 23 weeks of gestation in women with singleton pregnancies attending for routine antenatal care. The distribution of cervical lengths was established and the significance of differences in median cervical length between subgroups according to maternal age, ethnic origin, maternal ponderal index, cigarette smoking, alcohol drinking, drug abuse and previous obstetric history was calculated. In addition, 100 women were asked to complete a questionnaire aimed to assess the degree of discomfort, pain or embarrassment caused by the scan. In 100 pregnancies, cervical length was measured in each patient by two of four operators to determine intraobserver and interobserver variabilities. RESULTS During the study period, 2702 (80%) of the 3358 women attending for a 23-week scan agreed to participate in the study and, in all cases, the cervical length was measured successfully. The median cervical length was 38 mm and in 1.6% of cases the length was 15 mm or less. More than 90% of the women reported that the procedure was associated with no or only mild discomfort and embarrassment, whilst 85% found the ultrasound scan to be equally or less uncomfortable than a speculum examination. Measurement of cervical length was highly reproducible and, on 95% of occasions, the difference between two measurements by the same observer and by two observers was < or = 3.5 mm and < or = 4.2 mm, respectively. Cervical length was significantly shorter in women of Afro-Caribbean origin compared to Caucasians, those aged less than 20 years, those with a low ponderal index, those with a history of previous miscarriage or preterm delivery and in drug abusers. CONCLUSIONS Transvaginal sonographic measurement of cervical length is highly reproducible and it is associated with a minimal degree of discomfort to the patients. At 23 weeks, the median cervical length is 38 mm and, in 1.6% of the population, the length is 15 mm or less. There is an association between cervical length and demographic characteristics and previous obstetric history.