What counts as preterm

The NHS defines premature labour as labour that happens before the 37th week of pregnancy, and says "about 8 out of 100 babies will be born prematurely."

Not all of it is spontaneous. The NHS notes that some preterm births are planned and induced "because it's safer for the baby to be born sooner rather than later" — for example because of pre-eclampsia or a problem with the baby. Even then, the NHS says you can still make a birth plan and discuss your wishes.

The signs, and why people wait too long

The NHS says to call your midwife or maternity unit if you are less than 37 weeks pregnant and you have:

regular contractions or tightenings
period-type pains
a gush or trickle of fluid from your vagina — this could be your waters breaking
backache that is not usual for you

It adds a line worth taking literally: "You can also call your midwife or maternity unit if you're unsure or worried about anything."

Tommy's lists the same signs and adds a "show" — the plug of mucus that has sealed the cervix coming away, which may be a sticky jelly-like blob sometimes streaked with pink or brown blood, and which may come out gradually. Tommy's also says to call immediately at any stage of pregnancy for vaginal bleeding, a change or reduction in your baby's movements, or if you think your waters have broken.

The confusion is usually Braxton Hicks. Tommy's describes practice contractions as usually "uncomfortable rather than painful", not lasting long, not happening often, and not building up — and says to contact your maternity unit if contractions are painful. If you cannot tell, that is itself a reason to phone; nobody at the unit will think you wasted their time.

The HSE's Irish guidance on the signs of premature labour follows the same pattern.

What happens when you go in

The NHS says the midwife or hospital will offer checks, tests and monitoring to find out whether your waters have broken, whether you are in labour, and whether you have an infection. That may include a vaginal examination, blood test, urine test and cardiotocography to record contractions and the baby's heartbeat.

Behind that, NICE's preterm labour guideline sets out a fairly precise decision tree. If clinical assessment suggests suspected preterm labour and you are 29+6 weeks or less, NICE says to advise treatment straight away rather than test first.

At 30+0 weeks or more, NICE says to consider transvaginal ultrasound measurement of cervical length to judge the likelihood of birth within 48 hours: if the cervix is more than 15 mm, preterm labour is unlikely and going home can be discussed; if it is 15 mm or less, you are treated as being in diagnosed preterm labour. Where cervical length measurement is unavailable or unacceptable, NICE says to consider fetal fibronectin testing instead, with 50 ng/ml as the cut-off. NICE is explicit that the two tests should not be combined.

NICE also says that if neither test is done at 30 weeks or more, you should be treated as though you are in preterm labour. In other words, uncertainty is resolved in the baby's favour.

The three treatments, and what each is for

Steroid injections

These are for the baby's lungs, not to stop labour. NICE recommends offering maternal corticosteroids between 24+0 and 33+6 weeks where there is suspected, diagnosed or established preterm labour, a planned preterm birth, or preterm prelabour rupture of membranes, and says to consider them between 34+0 and 35+6 weeks. Between 22+0 and 23+6 weeks it is a discussion with you and the multidisciplinary team.

NICE also caps repeats: consider a single repeat course before 34+0 weeks if the last course was more than 7 days ago and birth is very likely within 48 hours, and "do not give more than 2 courses of maternal corticosteroids for preterm birth." The NHS notes steroids may not be offered after 36 weeks because the lungs are likely ready. The RCOG has a dedicated patient leaflet on corticosteroids that goes through the benefits and risks.

Magnesium sulfate

This is for the baby's brain. The NHS explains that if you are in premature labour at 24 to 29 weeks you should be offered magnesium sulfate through a drip to help protect brain development, and that it may also be offered at 30 to 33 weeks to reduce problems such as cerebral palsy. NICE's recommendations match, with the 23+0 to 23+6 week window treated as a discussion.

The NHS adds a practical caveat: prolonged use has in rare cases been linked to bone problems in newborns, so a baby may be offered extra checks if magnesium was used for more than 5 to 7 days or several times — but it also says it is very unlikely you would receive it for more than 24 hours.

Tocolysis — medicine to delay labour

NICE recommends offering nifedipine for tocolysis between 26+0 and 33+6 weeks where membranes are intact and labour is suspected or diagnosed, and considering it between 24+0 and 25+6 weeks. If nifedipine is contraindicated, NICE says to offer an oxytocin receptor antagonist, and not to use betamimetics at all.

The NHS is clear that this is not always the right call: slowing or stopping labour "is not appropriate in all circumstances", and the team will weigh how many weeks you are, whether it might be safer for the baby to be born — for example if there is infection or bleeding — the availability of local neonatal care, and your wishes. Buying 24 to 48 hours to complete steroids and, if needed, transfer you to a unit with the right cot is often the actual goal.

Preventive treatment before anything starts

The NHS lists who is offered this: people who have given birth before 34 weeks previously, had a miscarriage from 16 weeks, had waters break before 37 weeks in a previous pregnancy, or whose cervix has been injured, for example by surgery. A vaginal ultrasound scan between 16 and 24 weeks measures cervical length, and the NHS notes that a cervix shorter than 25 mm is linked to higher risk.

The two options are a progesterone pessary or a cervical stitch. NICE recommends offering a choice between them where there is both a history of spontaneous preterm birth up to 34+0 weeks (or loss from 16+0 weeks) and a cervical length of 25 mm or less on a scan between 16+0 and 24+0 weeks. ACOG's guidance on preventing spontaneous preterm birth covers the equivalent US approach.

What being born early actually means

The NHS puts it without euphemism: babies born before 37 weeks are vulnerable to problems associated with prematurity, and "the earlier in the pregnancy a baby is born, the more vulnerable they are." It says it is possible for a baby to survive if born from around 24 weeks, and that babies born that early need care on a neonatal unit with specialist facilities.

If preterm birth looks likely, ask specifically about which unit has a cot, whether transfer is being considered, and whether a neonatal team can speak to you before the birth. Those conversations are routine and you are entitled to them.

Preterm Labour