Routine second trimester cervical length screening in low risk women identified women at risk of a 'very' preterm birth but did not reduce the preterm birth rate: a randomised study from India.

Women (n = 300) at 'low risk' for a preterm birth (PTB), a singleton pregnancy and for a 16-24 week period of gestation (POG) were randomised to undergo cervical length (CL) measurement by transvaginal sonography (TVS) or not. The aim was to see if routine CL measurement and treatment of a short CL reduced the PTB rate. 'Low risk' was defined by an absence of a prior abortion or PTB of a singleton infant (>16 to <37 weeks) due to a spontaneous preterm labour (PTL) or a preterm pre-labour rupture of membranes (pPROM). The PTB rate was similar in the screened and unscreened group (10.3 and 8%, respectively, p = .433). In the screened group, women who delivered at 'term' or 'moderate to late' preterm (32 to <37 weeks) had a significantly higher mean CL (3.46 ± 0.41 and 3.48 ± 0.65 cm, respectively) than the women who delivered 'very' preterm (28 to 31 + 6 weeks; 2.05 ± 0.5 cm; p = .01). A short CL ≤2.5 cm was observed in two primigravidas (2/147 or 1.3%). They delivered at 28 + 3 and 30 + 6 weeks POG, respectively, despite treatment with vaginal progesterone and rescue cerclage in one. Their neonates were discharged in a good condition. In our low risk cohort, a routine second trimester CL measurement did not reduce the overall PTB rate. However, it identified two primigravidas at risk of having a 'very' PTB.Clinical Trials Registry (CTRI), India: Registration number CTRI/2016/01/010438 Impact statement What is already known on this subject? In women with a singleton pregnancy who are at a 'low risk' for preterm birth (PTB), a short cervical length (CL) at mid trimester measured by transvaginal sonography (TVS) identifies those at risk for a PTB. This risk may be reduced by the treatment with vaginal progesterone. At present, though evidence in favour of CL measurement in low-risk women exists, it is not established as a part of antenatal care. What do the results of this study add? A routine second trimester CL measurement in low risk women did not reduce the PTB rate. However, screening for a short CL helped to identify two primigravidas at risk for a 'very' PTB. It may be possible that detection and treatment of a short CL averted an 'extremely' PTB (<28 weeks) in these two women. What are the implications of these findings for clinical practice and/or further research? Future studies should assess the outcome of women with a short mid-trimester CL to see whether its treatment resulted in pregnancy prolongation and an improved neonatal outcome.

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