Short cervix without prior preterm birth: progesterone alone stays the benchmark

Design

Systematic review and Bayesian network meta-analysis of 26 RCTs

Population

8,561 asymptomatic women with singleton pregnancy, sonographic short cervix, no prior spontaneous preterm birth

Primary outcome

Preterm birth before 34 and 37 weeks

Effect

Vaginal progesterone vs control, birth <34 weeks RR 0.56 (95% CI 0.44 to 0.72), high certainty

A Bayesian network meta-analysis brought together 26 randomised trials (8,561 women) of interventions for asymptomatic singleton pregnancies with a short cervix on ultrasound and no previous spontaneous preterm birth. Published in BMJ Medicine on 12 October 2026.

In direct comparisons, vaginal progesterone alone reduced preterm birth before 34 weeks with high-certainty evidence (RR 0.56, 95% CI 0.44 to 0.72). In the network, it ranked highly for birth before 34 and 37 weeks. The pessary-plus-progesterone combination ranked first for efficacy, but combinations carried more maternal adverse events than progesterone alone (RR for progesterone vs combinations 0.56, 0.42 to 0.76) and rested on lower-certainty evidence.

The authors conclude that vaginal progesterone alone should remain standard care, with combinations kept to research settings and a pessary a possible alternative in selected women. For most units this confirms current practice rather than changing it, and it is a useful answer when a combination is proposed on the strength of rankings alone.

• Offer vaginal progesterone to women with a short cervix and no prior spontaneous preterm birth, in line with local guidance
• Do not add a pessary or cerclage routinely on the basis of network rankings
• Reserve combination regimens for trials or specialist decision-making
• Discuss a pessary only in selected women where progesterone is unsuitable
• Confirm the measurement is transvaginal before starting treatment

Why it matters

A top ranking in a network meta-analysis is not a reason to stack interventions that add harm without stronger evidence.

Don't overread it

The combination's first-place ranking comes from indirect, lower-certainty comparisons and is not proof it works better.

The statistics, in plain English

A risk ratio of 0.56 means preterm birth before 34 weeks was about 44% less likely with vaginal progesterone, and the whole interval sits below 1.0. Network rankings show which option is most likely best, not by how much; a high rank built on few or indirect trials can move as evidence accumulates.

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