Written by Ada’s Medical Knowledge Team
What is premature labor?
Premature labor, or preterm labor, is labor that begins after the 20th week and before the 37th week of pregnancy. Labor is defined as the the beginning of regular contractions and the shortening of the cervix (opening of the womb). Most cases of premature labor occur between the 34th week and the 37th week.
Premature labor is relatively common, taking place in roughly 7 in 100 single baby births. In pregnancies of twins or triplets, premature labor is even more common – the average delivery date for twins is the 37th week and for triplets, the 33rd week. A variety of other factors, including smoking and drinking alcohol during pregnancy, can also make premature labor more likely.
Roughly 1 in 10 cases of premature labour will result in a premature birth. In cases where the baby is sufficiently developed to survive after birth (usually babies older than 34 weeks), labor will generally be allowed to progress naturally. If the baby is less developed (pre-34 weeks), a variety of methods can be used to delay labor until the baby is sufficiently mature.
Causes of premature labor
In many cases, the cause of premature labor cannot be clearly identified. However, several factors are known to make premature labor more likely.
- Womb or cervical abnormalities
- Carrying twins or triplets
- Excess fluid in the womb (polyhydramnios)
- Placenta praevia (when the placenta attaches near or over the cervical opening)
- Cervical insufficiency (when the cervix begins to open prematurely)
- Fertility treatment (for the current pregnancy)
- Less than six months between two pregnancies
- Premature birth in previous pregnancy
- Premature rupture of membranes (waters breaking before labor has begun) in a previous pregnancy
- Late miscarriage in a previous pregnancy
Factors concerning the pregnant woman’s health can also make premature labor more likely. These include:
- Having a urinary tract infection
- High blood pressure
- Preeclampsia, eclampsia or HELLP syndrome
- Problems with blood clotting
- Drinking alcohol during pregnancy
- Use of illegal drugs during pregnancy
- Being under 18 or over 35 years old
Vaginal infections may also make premature labour more likely. These include:
- Bacterial vaginosis
- Infections caused by Group B streptococci.
Symptoms and warning signs of premature labor
The symptoms and warning signs of premature labor include:
- The waters breaking (rupture of the membranes). The pregnant woman may feel a soft popping sensation, followed by a slow trickle or gush of clear or pinkish liquid from the vagina. In some cases, there may only be an increase in vaginal discharge.
- If the waters break, contractions may begin. These may be regular and are often painless.
Other symptoms of premature labor include:
- An aching back
- Strong cramps (which may be painful)
- A need to urinate often
- Pressure in the pelvis
- Nausea, vomiting and/or diarrhoea
- The mucus plug in the cervix comes away
These symptoms may also occur if an individual is not in premature labor. However, a pregnant woman experiencing any of these symptoms should contact their doctor or midwife urgently.
Premature labor diagnosis
Diagnosis is usually made based on the symptoms and a physical examination. This will involve a gynecological exam to see if the cervix (the opening to the womb) has opened as well as general checks on the health of the mother and baby. This may include:
- Temperature, pulse and blood pressure checks
- A check of the baby’s heartbeat (to look for irregularities)
- A blood test and vaginal swab (to check for infection)
- An ultrasound
Premature labor treatment
- Allowing labor to continue naturally. This is generally advised in pregnancies of 34 weeks or more, when the baby will be sufficiently mature to survive outside of the womb. Nevertheless, the birth should still take place in a hospital where specialist care can be administered should it be necessary.
- Artificially delaying birth to allow time for doctors to prepare the baby for birth (usually steroids will be used to mature the baby’s lungs) and transfer the mother to a specialist care unit. This option will generally be advised in pregnancies of under 34 weeks. Birth will normally be delayed for at least 48 hours, and ideally for longer if needed. Due to the possible complications, this option is usually avoided if possible.
- Accelerating delivery using medication or caesarean section. This option will typically be chosen if the mother and/or baby are unwell.
Premature labor prevention
As the causes of premature labor are not always clear, prevention can be difficult. However, there are several steps a pregnant woman can take to help reduce the risk of premature labor.
Being tested for and treating infections can help to prevent some cases of premature birth. Receiving treatment for STIs is important during pregnancy, as is avoiding food poisoning by not eating certain foods (such as raw or undercooked meat, unpasteurized milk and pâté) and maintaining high general hygiene standards (washing the hands regularly, for example).
Certain lifestyle choices can also help reduce the risk of premature labor. Staying active through regular light exercise is generally advised for pregnant women – this will also boost overall wellbeing and help reduce the chances of conditions such as diabetes and preeclampsia, which can contribute to the onset of premature labor.
Premature labor complications
The earlier a premature baby is born, the greater the risk of complications. Possible complications include:
- Immature lungs are the main concern for babies born early. In most cases, a baby’s lungs are mature by roughly week 36 of pregnancy. Babies born earlier than this may be given steroids to help accelerate the maturation process.
Immature lungs can increase the risk of further complications. These include:
- Respiratory distress syndrome (RDS): A condition involving irregular breathing and a lack of surfactant – a substance that helps prevent the lungs from collapsing – in the lungs.
- Transient tachypnea: A condition characterized by rapid shallow breathing.
- Pneumonia: An infection of the lungs that can cause breathing problems.
Other possible complications include:
- Infection: Premature babies are at high risk of infection. For this reason, premature babies will be kept in an incubator to protect against bacteria.
- Jaundice: A yellowing of the skin caused by a lack of the substance bilirubin. See this resource on neonatal jaundice for further information.
- Anemia: A condition involving low levels of red blood cells in the blood.
Premature labor FAQs
Q: What happens if my waters break but I am not in labor?
A: It is possible for the waters to break but for a woman to not be in labor, this is called preterm prelabor rupture of the membranes (P-PROM). If this happens, in most cases antibiotics will be administered to prevent infection (made more likely by the breaking of the waters) and steroids given to help mature the baby’s lungs. Doctors will generally aim to delay the birth until at least 34 weeks and after this induce labor artificially.
Other names for premature labor
- Premature birth
- Premature newborn
- Preterm birth
The American College of Obstetricians and Gynecologists. “Preterm (Premature) Labor and Birth: Resource Overview.” November, 2016. Accessed May 15, 2018. ↩
Tommy’s. “How you can reduce your risk of premature birth.” June 1, 2017. Accessed May 16, 2018. ↩