Second trimester cervical length screening, in a low-risk European population

Purpose: The aim of this work is to assess cervical length (CL) distribution in a low-risk population in order to evaluate the applicability of a possible universal CL screening in the second trimester, aimed at preventing preterm birth (PTB).

Methods: In a multicentric, prospective cohort study, singleton pregnant women attending second trimester anatomy scan between 18 + 0 to 22 + 6 weeks of gestation were eligible. Teenage pregnancy and women with previous PTB were excluded. The recruitment occurred from February 2020 to December 2022. TVU CL was measured by expert sonographers, in 12 National Health Service (NHS) care clinics of Modena and Parma districts (Emilia-Romagna Region, Italy). Internal quality check of images was performed. Personal and obstetric history, as well as gestational age were collected. Primary outcomes were to define CL curves and the incidence of CL ≤25 mm in low-risk pregnant women Secondary outcomes were the incidences of PTB <37, <34, and <32 weeks.

Results: Among 3226 screened women, mean and median CL were 40.8 and 40 mm, respectively. The 10th centile was equal to 33 mm while 25 mm represented the 2nd centile of the distribution. The incidence of CL ≤25 mm (short cervix) was 1.25%. Among those women, 7.5% were shorter than 150 cm, opposed to 2.1% in the normal CL group (p = .02); in addition there were more nullipara, women ≥ 40 and smokers (p = .03). Women with short cervix were at higher risk of PTB (23.6 vs 4.3%; RR: 4.6, 95%CI 2.49-8.48). At multivariate analysis, both CL ≤ 25 mm (RR: 5.51, 95%CI: 2.45-12.3) and stature ≤150 cm (RR: 2.54, 95%CI: 1.11-5.79) resulted independent predictors for PTB, once adjusted for other risk factors (fibroids, cervical surgery, obesity, low education, older age, smoking habit).

Conclusion: Although our study confirmed that women with short cervix are more likely to deliver preterm, the low incidence of such risk factor means that most of the preterm births occurred among women with normal cervical length. Thus, in a low-risk Italian population, ineffectiveness of universal screening is forecast.