# Progesterone for Preterm Birth Prevention

> Indications by prior preterm birth or short cervix, vaginal versus 17-OHPC route and timing for NEET-PG Obstetrics and Gynaecology exam preparation.

- Canonical URL: https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/progesterone-for-preterm-birth-prevention
- Exam / course: NEET-PG · Subject: Obstetrics and Gynaecology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-08
- Last updated: 2026-10-08
- Reference basis: ACOG Practice Bulletin on Prediction and Prevention of Spontaneous Preterm Birth; Williams Obstetrics; D.C. Dutta's Textbook of Obstetrics
- How to cite: "Progesterone for Preterm Birth Prevention", PrepElephant, https://prepelephant.com/topics/neet-pg/obstetrics-and-gynaecology/progesterone-for-preterm-birth-prevention

## Direct answer

Progesterone for preterm birth prevention is indicated in singleton pregnancies with a previous spontaneous preterm birth or a short cervix on mid-trimester ultrasound. Weekly intramuscular 17-alpha hydroxyprogesterone caproate is the classic choice after a previous preterm birth, while vaginal progesterone is used for a short cervix. Progesterone is not recommended to prevent preterm birth in twin pregnancies, because trials show no reliable benefit there.

## What you must remember

- **Prior spontaneous preterm birth:** 17-OHPC 250 mg intramuscularly weekly, started between 16 and 24 weeks and continued to about 36 weeks.
- **Short cervix:** vaginal progesterone 200 mg nightly for a singleton with cervical length below about 25 mm, with thresholds varying between guidelines.
- **Route choice:** vaginal progesterone for a short cervix; intramuscular 17-OHPC for prior preterm birth where it is available.
- **Twin pregnancies:** not recommended for preventing preterm birth.
- **Mechanism:** maintains myometrial quiescence and supports cervical integrity.
- **Availability:** 17-OHPC was withdrawn from the United States market in 2023 after the PROLONG trial failed to confirm benefit, so vaginal progesterone is increasingly used for prior preterm birth too; textbooks and exams still cite 17-OHPC.

## A timed pathway from indication to stopping

Progesterone is a preventive therapy with a defined indication, a defined start and a defined stop. The steps below set out that sequence.

1. **Identify the indication:** a previous spontaneous preterm birth, or a short cervix on scan, in a singleton pregnancy.
2. **Check the start point:** 17-OHPC starts between 16 and 24 weeks, and vaginal progesterone starts once the short cervix is found in mid-trimester.
3. **Choose the route:** vaginal progesterone for a short cervix, and intramuscular 17-OHPC for prior preterm birth where available.
4. **Continue to the target:** continue treatment until about 36 weeks for either route, as per protocol.
5. **Review if labour starts:** progesterone does not treat established preterm labour; tocolysis, corticosteroids and transfer follow standard protocols.

The indication must match the pregnancy. Progesterone has no role in twins, and it is not a rescue treatment once labour begins. Exam questions usually give a history or a scan finding first, so the indication must be named before the drug. Stopping at about 36 weeks is as important as starting on time, and a woman already in labour falls outside the preventive pathway.

## Where the exam tries to catch you

Questions in this area separate prevention from treatment and singleton from twin pregnancy.

- **Trap:** Prescribing progesterone to every woman with threatened preterm labour. **Correct:** Progesterone prevents recurrence in defined indications and does not treat active labour.
- **Trap:** Using 17-OHPC in twin pregnancy. **Correct:** Progesterone is not recommended for preventing preterm birth in twins.
- **Trap:** Confusing progesterone for preterm birth prevention with progesterone for threatened miscarriage. **Correct:** The indications, gestations and trial evidence differ.

## Frequently asked questions

### Who should receive 17-OHPC for preterm birth prevention?

Women with a singleton pregnancy and a previous spontaneous preterm birth are the classic indication for 17-OHPC. Weekly intramuscular injections are started between 16 and 24 weeks. Progesterone for preterm birth prevention is therefore tied to a documented obstetric history.

### What is the vaginal progesterone dose for a short cervix?

Vaginal progesterone 200 mg nightly is the standard dose for a singleton pregnancy with a short cervix on mid-trimester scanning. The cervical length threshold for treatment varies by guideline. Treatment is usually continued until around 36 weeks.

### Is progesterone useful in twin pregnancies?

Progesterone is not recommended to prevent preterm birth in twin pregnancies. Trials have not shown reliable benefit in this group. Twin pregnancies are managed with cervical length surveillance and other preventive strategies instead.

### Can progesterone stop preterm labour that has already started?

Progesterone is not a treatment for established preterm labour. Its role is prevention in women with a defined risk. Active preterm labour is managed with tocolysis, corticosteroids and transfer as indicated.