Cervical length, risk factors, and delivery outcomes among women with spontaneous preterm birth

Objectives: To evaluate differences in risk factors and delivery outcomes among women with spontaneous preterm birth (sPTB) with short (<= 25 mm) versus normal (>25 mm) cervical length (CL). Methods: Secondary analysis of a prospective cohort study of singleton gestations between 18 0/7 and 23 6/7 weeks, without prior sPTB, undergoing universal transvaginal CL screening between 1 January 2012 and 31 December 2013. Only women with sPTB (<37 0/7 weeks) were included. Demographic characteristics, risk factors for sPTB, delivery outcomes and presentation of PTB were collected. The primary outcome was mean number of risk factors. Results: The cohort included 2071 women, of which 145 (7%) had PTB and 84 (4%) had sPTB. Sixty-nine (82%) women with sPTB had a CL >25mm and 15 (18%) had a CL <= 25 mm. Women with a short CL did not differ from women with normal CL with respect to demographic variables or mean number of risk factors (4.20 +/- 2.11 versus 3.52 +/- 1.97, p = 0.23), but they did deliver at a significantly earlier gestational age (25.0 +/- 1.1 versus 34.6 +/- 3.1 weeks, p<0.01). The distribution of the presentation of sPTB was different in women with a short versus normal CL (p<0.01). Conclusions: Among women with sPTB, women with a short CL had similar number of risk factors, but were more likely to deliver at a significantly earlier gestational age. A short CL identifies women at risk for very early sPTB.