Management of threatened preterm labor based on cervical length: a randomized controlled trial

A substantial proportion of women with threatened preterm labor do not deliver imminently, frequently receiving unnecessary tocolytic agents and antenatal corticosteroids. The objective of this study is to evaluate whether the use of cervical length measurement in managing threatened preterm labor can reduce inappropriate treatment.

A randomized controlled trial was conducted involving patients presenting with threatened preterm labor between 24 and 33^+ 6 weeks of gestation. Patients exhibiting a transvaginal cervical length between 15 and 30 mm were randomized into two groups: (1) the expectant group; and (2) the treatment group. The expectant group received no treatment, while the treatment group received standard corticosteroids and tocolytic agents. The measurements of cervical length in the expectant management group were performed every 2 h if there were regular uterine contractions with intervals of less than 10 min or every 4 h if the contractions occurred at intervals > 10 min or were irregular until there was no uterine contraction. Corticosteroids and tocolytics were administered only if cervical shortening > 20% from the baseline value or cervical length measured below 15 mm. The primary outcome was inappropriate treatment, defined as undelivered for more than a week after a complete course of corticosteroid treatment or spontaneous preterm delivery within 7 days of recruitment without corticosteroid administration.

One hundred fifteen patients were identified, and 65 cases were excluded. Among the 50 recruited cases, 26 were randomized to the expectant group and 24 to the treatment group. Expectant management leads to a significant 92% reduction in inappropriate treatment [7.7% vs. 98.5%; RR 0.08; 95% CI: 0.02-0.31]. There were significantly lower rates of maternal tachycardia, hypotension, and hypokalemia, as well as a shorter median maternal stay (p < 0.05 for all) in the expectant group.

Patients with threatened preterm labor whose cervical length is within 15-30 mm without additional cervical shortening can be safely managed expectantly. This approach reduces maternal side effects and shortens maternal hospital stays.

This study was retrospectively registered at the Thai Clinical Trials Registry (Registration Number: TCTR20250218004) on February 18, 2025 (Date of registration) was conducted and reported in accordance with the Consolidated Standards of Reporting Trials (CONSORT) 2010 Statement.