A short cervix, measuring ≤25 mm in length, in the second trimester of pregnancy is considered a harbinger of spontaneous preterm birth. To investigate if 25mm was the accurate cut-off length to define a short cervix among asymptomatic pregnant women during the mid-trimester, researchers from Israel conducted a retrospective study, wherein they also analysed the maternal and neonatal outcomes in these women. For this they enrolled 1483 women with singleton pregnancies and cervical length of ≤25 mm detected on ultrasound at midtrimester and compared the outcomes with women with symptomatic cervical shortening and women with normal cervical length.

The preterm birth rate, which was the primary outcome of the study, was comparable between women with asymptomatic cervical shortening (4.9%) and those with normal cervical length (3.8%). However, the use of antenatal steroids, a secondary study outcome, was substantial in women with asymptomatic cervical shortening (78.2%) compared to 7.4% in women with normal cervical length.

Compared to the women with normal cervical length, the risk of early preterm birth was significantly higher in women with cervical length of ≤15 mm; 3.6% vs 47.2%, respectively. The late preterm birth rate was also considerably higher in women with cervical length of ≤15 mm; 3.8% vs 35.8%, respectively.

Based on these findings, it was concluded that while asymptomatic cervical length of 15-25 mm did not increase the odds of preterm birth, a cervical length of ≤15 mm was significantly associated with risk of preterm delivery.

Reference

1. Lauterbach R, et al. Is 25 mm the correct mid-trimester cut-off for cervical shortening among asymptomatic women? Int J Gynaecol Obstet. 2023 Apr;161(1):218-224. doi: 10.1002/ijgo.14396.