Preterm birth

A full-term pregnancy lasts around 40 weeks, usually between 38- and 42-weeks’ gestation. A preterm baby is born before 37 weeks and often has more health problems than a full-term baby. The World Health Organization describes the degree of prematurity as late moderate to late preterm (32-37 weeks and most common), very preterm (28-32 weeks) or extremely preterm (less than 28 weeks).

Globally about 15 million babies – up to one in ten – are born preterm each year and this rate is increasing.

In Australia, 8.6 per cent of babies are born preterm. That rate is higher in mothers who smoke during pregnancy (13 per cent) and in most Indigenous (14 per cent) and remote communities (13 per cent). Mothers aged under 20 and over 40 have higher rates of preterm babies (11 and 12 per cent), as do multiple births, including 63 per cent of twins and all babies born as triplets or more.

The World Health Organization says that across 184 countries, the rate of preterm birth ranges from 5-18 per cent. In low-income settings, half the babies born at or below 32 weeks die due to a lack of feasible, cost-effective care. In high-income countries, almost all these babies survive.

It is rare for babies born before 22 weeks of pregnancy to survive. Survival rates rapidly increase for those born after 23 weeks, reaching 80-90 per cent at 28 weeks if treated in a high-level neonatal intensive care unit (NICU), but these infants may face serious and possibly lifelong disabilities. The longer a pregnancy has progressed, the more likely the baby will be born without long-term complications.

The introduction of corticosteroid injections to mothers within 48hrs of delivery in the 1970’s has greatly reduced death and disability rates in infants born under 28 weeks. Marked improvements in the care of these infants in the hours to days after birth has also increased survival rates, but the risk of disability (eg cerebral palsy and learning delays) and long-term morbidity (particularly chronic lung disease) remain stubbornly high, particularly in infants born extremely premature.

Most babies born extremely preterm will experience significant problems immediately after birth. The single greatest challenge they face is to clear the liquid that has filled their airways throughout fetal life so that air can enter their lungs and the baby can start air breathing.

While most preterm babies will try to breathe after birth, their efforts are usually weak and ineffective and so most infants will require help to start air-breathing. However, it is still unclear what is the best approach to assist these infants without damaging their immature lungs. As stimulating the baby to breathe is thought to be very important, avoiding low oxygen levels are also important, as these inhibit breathing.

Respiratory support is mostly provided using a face mask and may also involve the use of artificial breathing if the infants own breathing is insufficient. The infant will be placed in a plastic wrap to keep it warm.

In the hours to days after birth, preterm infants are at high risk of jaundice, bleeding in the brain, anaemia and infections. They may also have problems breathing unassisted, maintaining blood pressure and a good circulation and develop digestive problems. Some cannot regulate their body temperature, breathing or heart rate.

If preterm labour progresses, some medications can improve the baby’s survival prospects and reduce complications. They may include antenatal corticosteroids to mature the baby’s lungs and other organs, magnesium sulfate to decrease the risk of cerebral palsy, and antibiotics to prevent infection if the waters have broken.

Recent research has indicated that, at delivery, there is a significant benefit for the baby to remain attached to the umbilical cord, next to the mother, while it is stimulated to breathe, or it receives respiratory support. This is often called ‘delayed cord clamping’, but is more correctly called ‘physiological based cord clamping’ to avoid a focus on time as the time needed by each infant is different.

Most preterm babies can develop normally but may be at increased risk of developmental problems. Long-term effects can include growth, movement, vision, hearing, social and emotional problems, cerebral palsy, language delays, dental problems, thinking and learning difficulties and chronic conditions such as asthma. They may also be at increased risk of sudden infant death syndrome (SIDS).