Preventing Preterm Birth With Twins

The number everything starts from

NICE NG137 says teams should explain that about 60 in 100 twin pregnancies result in spontaneous birth before 37 weeks, and about 75 in 100 triplet pregnancies result in spontaneous birth before 35 weeks. The NHS gives the same figures as around 6 in 10 twins born before 37 weeks and almost 8 in 10 triplets before 35 weeks. RCOG repeats them, and adds that around 8 in 100 babies overall are born prematurely.

Those are spontaneous births, not planned ones. They describe labour starting on its own.

The one screening test that is offered

NG137 was updated in 2024 to recommend a single cervical length scan between 16 and 20 weeks for everyone with a twin or triplet pregnancy. Twins Trust, whose page on this was written with that change in mind, says it is offered to all women carrying twins regardless of chorionicity, because dichorionic twins remain at increased risk of spontaneous preterm birth and monochorionic twins carry placental problems on top of that.

The NHS describes the same scan as being offered between 16 and 20 weeks to help assess your risk of giving birth prematurely. Twins Trust adds that it is a screening test, so it is not repeated unless you develop new symptoms of concern such as bleeding, watery discharge, abdominal pain or cramps, and that the scan itself does not cause preterm birth or miscarriage.

What a short cervix leads to

NG137 says teams should discuss that if a cervical length scan shows a short cervix, 25 mm or less, treatment with progesterone may reduce the risk of preterm birth, and should offer vaginal progesterone where the cervix measures 25 mm or less, continuing until 34 weeks or birth if sooner. The same applies if a cervical length of 25 mm or less is found incidentally on a scan between 20 and 24 weeks. We are not quoting doses here; that conversation belongs with the person prescribing.

Twins Trust is refreshingly honest about the strength of the evidence. It says the scientific evidence for treating a short cervix in twins is not strong, mainly because few studies have been done in twin pregnancies, that there is some evidence of a lower chance of preterm birth in twins treated with progesterone, and that there is no evidence of benefit in triplets but that treatment is reasonable given the high risk.

What NICE says not to offer

This is the most useful list in the guideline, because it names things that are still discussed in forums and occasionally still offered. NG137 says not to offer the following, alone or in combination, routinely to prevent spontaneous preterm birth in a twin or triplet pregnancy: an arabin pessary, bed rest, cervical cerclage, or oral tocolytics. Separately, it says not to offer intramuscular progesterone.

Bed rest deserves a moment. It is the intervention people most often impose on themselves, and it appears on the list of things not to offer.

Tests that are not used to predict it

NG137 also rules out two prediction tools. It says not to use fetal fibronectin testing alone to predict the risk of spontaneous preterm birth in twin and triplet pregnancy, and not to use home uterine activity monitoring for the same purpose. If you have seen either recommended for singletons, that is why they may come up.

NG137 further says not to offer screening for fetal growth restriction or feto-fetal transfusion syndrome in the first trimester, which is a different question but often gets folded into the same anxiety.

What screening can and cannot do

Twins Trust answers this directly: having a cervical length scan will help determine the chance of preterm birth, but will not prevent it. Treatment with progesterone may prevent a preterm birth but is not a guarantee, and some women with a normal measurement and some with a treated short cervix will still give birth early.

That is worth absorbing before the scan rather than after. A reassuring measurement is genuinely reassuring, but it is not a promise.

Steroids are not prevention

Antenatal corticosteroids do not stop preterm birth; they help a baby's lungs cope with being born early. NG137 says women should be informed of their increased risk of preterm birth and about the benefits of targeted corticosteroids, and then says explicitly not to use single or multiple untargeted or routine courses of corticosteroids in twin or triplet pregnancy, and to inform women that there is no benefit in untargeted administration.

Twins Trust adds useful context for multiples: twins have been less well studied here, evidence between 35 and 39 weeks is less clear, and RCOG advises that after 34 weeks doctors should discuss the potential benefits and drawbacks so you can make an informed choice. The NHS notes that steroids may not be offered after 36 weeks because a baby's lungs are likely to be ready.

Knowing the signs still matters

Twins Trust points out that premature tightenings can be part of normal pregnancy, especially with twins, but that it is always safest to contact your midwife or maternity unit if you are unsure. The NHS lists the checks a unit will do, and notes that if preterm labour starts it is sometimes possible to slow it briefly, which buys time for steroids and for the neonatal team to prepare.

Prevention is a short list. Recognition is not, and it is the part that is actually within your control.