Premature Birth

Categories of preterm birth

Babies born around 22 to 25 weeks are considered periviable: survival is possible with intensive care but not certain, and long-term disability is more common. Survival rises sharply with each additional week.

Causes and risk factors

About half of preterm births follow spontaneous preterm labor or early rupture of membranes; others are planned early deliveries because of health problems in the mother or baby.

Risk factors

• previous preterm birth, the strongest risk factor
• twins, triplets or more
• short cervix on ultrasound, or cervical insufficiency
• uterine abnormalities or previous cervical surgery
• infections: urinary, vaginal (bacterial vaginosis) and amniotic fluid infections
• preeclampsia and high blood pressure
• placental abruption or placenta previa
• diabetes and other chronic conditions
• intrauterine growth restriction
• smoking, alcohol and drug use
• pregnancy less than 18 months after a previous birth
• age under 17 or over 35
• stress, low income and limited access to prenatal care; in the US, Black women have higher rates, reflecting structural inequities

Warning signs of preterm labor

See preterm labor for details. Signs before 37 weeks include:

• contractions every 10 minutes or more often, which may feel like the belly tightening
• menstrual-like cramps or a dull low backache
• pelvic pressure, as if the baby is pushing down
• a change in vaginal discharge: watery, mucus-like or bloody
• fluid leaking from the vagina

If you notice these, contact your provider or labor unit immediately.

Care when preterm birth is likely

• Antenatal corticosteroids: given to the mother between 24 and 34 weeks (and sometimes later), they speed up the baby's lung development and reduce breathing problems, brain bleeding and death.
• Magnesium sulfate: given before 32 weeks to reduce the risk of cerebral palsy.
• Tocolytics: medicines that can delay labor for up to 48 hours, allowing steroids to work and transfer to a hospital with a NICU.
• Antibiotics: for group B strep or when membranes rupture early.
• Delivery at a hospital with an appropriate NICU.

Prevention in future pregnancies

• Vaginal progesterone for people with a short cervix.
• Cervical cerclage: a stitch around the cervix for selected people with cervical insufficiency or previous preterm birth with a short cervix.
• Low-dose aspirin for those at high risk of preeclampsia, as prescribed.
• Stopping smoking, treating infections, and spacing pregnancies.

Health problems in premature babies

Short-term

• Breathing problems: respiratory distress syndrome and apnea of prematurity.
• Temperature control and low blood sugar.
• Feeding difficulties: many need tube feeding at first.
• Jaundice.
• Infections.
• Brain bleeding (intraventricular hemorrhage).
• Necrotizing enterocolitis: a serious bowel inflammation.
• Patent ductus arteriosus: a heart vessel that fails to close.

Long-term

• Bronchopulmonary dysplasia (chronic lung disease)
• Retinopathy of prematurity and vision problems
• Hearing loss
• Cerebral palsy and developmental delays
• Learning and behavior difficulties, including ADHD

Risks are much higher in babies born before 28 weeks.

In the NICU

Premature babies may need incubators, breathing support (CPAP or ventilators), IV nutrition, tube feeds, phototherapy and monitoring. Parents are encouraged to provide breast milk, which protects against infection and necrotizing enterocolitis, and skin-to-skin (kangaroo) care. Babies usually go home around their original due date once they can breathe, feed and keep warm independently.

After discharge, follow-up includes hearing and eye checks, growth monitoring, developmental assessments and RSV prevention.

Outlook

Most babies born after 32 weeks do very well. Survival for babies born at 28 weeks is over 90% in US NICUs, and many extremely premature children go on to live healthy lives, though some have lasting effects. Early intervention services support development.

Frequently asked questions

What is considered a premature birth?

A birth before 37 completed weeks of pregnancy is premature. It is divided into late preterm (34 to 36 weeks), moderately preterm (32 to 33), very preterm (28 to 31) and extremely preterm (under 28 weeks).

What are the signs of preterm labor?

Signs include regular contractions or tightening every 10 minutes or more often, menstrual-like cramps, a dull low backache, pelvic pressure, a change in vaginal discharge, or leaking fluid before 37 weeks. Contact your provider right away.

What causes premature birth?

Common causes and risk factors include a previous preterm birth, twins or more, a short cervix, infections, preeclampsia, placental problems, smoking and short gaps between pregnancies. In many cases, no clear cause is found.

How early can a baby be born and survive?

Some babies born at 22 to 23 weeks survive with intensive care, but risks of death and disability are high. Survival improves significantly with each week, and most babies born after 28 weeks survive.