Preterm Labor

What preterm labor is

Labor is the process of regular contractions that dilate and thin (efface) the cervix so the baby can be born. When this starts after 20 weeks but before 37 completed weeks, it is preterm labor. If the baby is born, it is a premature birth.

Preterm labor is not always progressive. Many people with preterm contractions have no change in the cervix and go on to deliver at term. That is why assessment in hospital is so important: it separates true preterm labor from false alarms and lets treatment start quickly when needed.

Signs of preterm labor

• Contractions: the belly tightens like a fist every 10 minutes or more often. They may be painless.
• Menstrual-like cramps low in the belly, which may come and go or be constant.
• A dull, low backache, constant or in waves.
• Pelvic pressure: a feeling that the baby is pushing down.
• Change in vaginal discharge: more of it, or watery, mucus-like or bloody.
• Fluid leaking from the vagina.
• Abdominal cramps with or without diarrhea.

What to do if you think you are in preterm labor

1. Stop what you are doing. Empty your bladder, then lie down on your left side.
2. Drink 2 to 3 glasses of water.
3. Time the contractions from the start of one to the start of the next, for one hour.
4. Call your provider or go to labor and delivery if you have 6 or more contractions in an hour, any fluid leaking, bleeding, or symptoms that do not ease. Do not wait for symptoms to become painful.

Preterm labor vs Braxton Hicks contractions

If you are unsure, get checked. It is always safer to be assessed and sent home than to miss preterm labor.

Causes and risk factors

Often no single cause is found. Known contributors include:

• a previous preterm birth, the strongest risk factor
• a short cervix on ultrasound, or cervical insufficiency
• twins, triplets or more, or too much amniotic fluid
• infections, including urinary tract infections, bacterial vaginosis, sexually transmitted infections and infection of the membranes (chorioamnionitis)
• bleeding in pregnancy, including placental abruption and placenta previa
• uterine abnormalities or previous cervical surgery such as a cone biopsy
• high blood pressure, preeclampsia, diabetes and other chronic conditions
• pregnancies less than 18 months apart, IVF pregnancies
• smoking, alcohol and drug use, high stress and low or very high body weight
• age under 17 or over 35

Black women in the US have higher preterm birth rates, a gap linked to structural inequities and stress rather than biology alone.

How preterm labor is diagnosed

At labor and delivery, the team will:

• monitor contractions and the baby's heart rate
• do a sterile speculum exam to check for leaking fluid, bleeding and infection, and take swabs, including for group B strep
• check the cervix by examination or by transvaginal ultrasound to measure its length
• in some cases, test for fetal fibronectin (fFN), a protein in vaginal fluid. A negative result between 24 and 34 weeks makes birth in the next 2 weeks very unlikely
• check urine for infection and blood pressure for preeclampsia
• do an ultrasound to check the baby's position, size and amniotic fluid

Preterm labor is diagnosed when there are regular contractions with cervical change, or with significant dilation on arrival.

Treatment

Treatment can rarely stop preterm labor for long, but it buys time for measures that protect the baby.

• Corticosteroids (betamethasone or dexamethasone): two injections, usually given 24 hours apart, between about 24 and 34 weeks. They speed up lung and brain development and reduce the risk of breathing problems, bleeding in the brain and death. They work best when birth happens at least 24 to 48 hours later, but help even with less time. Some people at 34 to 36 weeks are also offered them.
• Magnesium sulfate: given by IV when birth seems likely before 32 weeks, to lower the risk of cerebral palsy.
• Tocolytics: medicines such as nifedipine or indomethacin that slow contractions for up to 48 hours, to allow steroids to work or transfer to a hospital with a neonatal intensive care unit (NICU). They are generally used between about 24 and 34 weeks.
• Antibiotics: for group B strep if status is positive or unknown, and for infection or early rupture of membranes.
• Transfer to a hospital with the right level of NICU care, if time allows.

Bed rest is no longer recommended to prevent preterm birth, because it does not help and carries risks such as blood clots and muscle loss.

If preterm labor stops, you may go home with advice to watch for signs. If it does not, the team prepares for a preterm birth.

Preventing preterm labor

For people at higher risk, options include:

• Vaginal progesterone for a short cervix found on ultrasound in a singleton pregnancy.
• Cervical cerclage, a stitch placed around the cervix, for selected people with a short cervix and a previous preterm birth, or cervical insufficiency.
• Low-dose aspirin from 12 to 28 weeks for people at high risk of preeclampsia.
• Cervical length screening by ultrasound in mid-pregnancy.
• Treating urinary infections, stopping smoking, early and regular prenatal care, and spacing pregnancies at least 18 months apart.

Note that 17-OHP injections (Makena) were withdrawn from the US market in 2023 after studies found they did not reduce preterm birth.

Frequently asked questions

What are the first signs of preterm labor?

Early signs include contractions every 10 minutes or more often, menstrual-like cramps, a dull low backache, pelvic pressure and a change in vaginal discharge to watery, mucus-like or blood-tinged. Contact your provider promptly if you notice any of these before 37 weeks.

Can preterm labor be stopped?

Sometimes contractions stop on their own, and medicines called tocolytics can delay labor for up to about 48 hours. This is usually not enough to prevent preterm birth, but it allows steroid injections and magnesium to protect the baby, and time to transfer to a hospital with a NICU.

How do I know if it's Braxton Hicks or preterm labor?

Braxton Hicks contractions are irregular, do not get stronger and usually ease with rest, water or a change in position. Preterm labor contractions become regular and closer together, and may come with backache, pressure, bleeding or fluid leaking. If in doubt, get checked.

What happens at the hospital if I'm in preterm labor?

The team monitors your contractions and baby, checks your cervix, often with an ultrasound, takes swabs, and may test for fetal fibronectin. If labor is confirmed, you may receive steroid shots, magnesium sulfate, medicines to slow contractions and antibiotics.

Does preterm labor mean my baby will be born early?

Not necessarily. Many people with preterm contractions do not have cervical change and deliver at term. Even true preterm labor sometimes stops. If the baby is born early, outcomes improve greatly with each extra week and with steroid treatment beforehand.