What is a preterm birth?

An infant is considered to be preterm when born prior to 37 weeks of gestation (WG) or 8 months. A baby born between 37 and 41 WG is said to be “full term”, the normal length of pregnancy. But not all cases of prematurity are the same: the earlier the birth, the less the baby will be mature and the less able to adapt to extrauterine life. Prematurity is defined as:

  •  Moderately preterm: the birth occurs between 7 and 8 months (i.e. 32 and 37 WG), 
  • Very preterm: the birth occurs between 6 and 7 months (i.e. 28 and 32 WG), 
  • Extremely preterm: the birth occurs before 6 months (i.e. before 28 WG).

Preterm births around the world

Fifteen million babies are born too soon every year. Preterm birth is a significant public health problem in all low-, middle-, and high-income countries. Prematurity is the leading cause of newborn deaths (babies in the first 4 weeks of life) and now the second leading cause of death in children under the age of 5 (Born Too Soon, WHO 2020). Three-quarters of these deaths could be prevented through routine, effective, and low-cost interventions, even without intensive care.

Some of the children who survive will have neurological sequelae (motor, intellectual, sensory, etc.), pulmonary disease (bronchopulmonary dysplasia, apnea), or sequelae of necrotizing enterocolitis. The frequencies of these sequelae vary according to the country.

Reducing the frequency of preterm birth and preventing its complications is a major public health issue. 

Preterm births in France

In France, in 2015, prematurity represented 7.1% of live births or 54,000 births per year. France is 14th among European countries, far behind the Baltic countries (Lithuania 5.4%, Latvia 5.8%, Estonia 5.7%), the Scandinavian countries (Sweden 5.6% Finland 5.8%, Norway 6.2%), and others like Iceland 6.1%, Ireland 6.5%, and the Netherlands 6.9% (Euro-Peristat Report 2015).

Perinatal mortality rate is an indicator of maternal and infant health and of the quality of perinatal care (pregnancy, childbirth, and postnatal period [up to 28 days]). In France, the rate is average for a high-income country and did not improve between 2010 and 2015.

Figure : Neonatal mortality rates at and after 24 WG
(Euro-Peristat Report 2015)

Spontaneous preterm births and induced preterm births: does it make a difference?

Spontaneous preterm birth occurs when no treatment is effective in stopping labor and delivery before 37 WG. The underlying etiologies could be premature rupture of membranes, infections, fever, uterine anomalies or spontaneous uterine contractions, the cause of which is not always known.

Induced preterm birth follows a medical decision to prevent a high risk to the mother (pre-eclampsia, hemorrhage, or management of a maternal disease) or to the fetus (e.g. fetal growth retardation).

Other risk factors are associated with preterm birth: multiple pregnancy, fetal growth retardation, unfavorable socioeconomic situations, mother’s age, tobacco use,… Very little is known about the mechanisms of preterm birth. 

The consequences of a preterm birth

The implications of being born too soon extend throughout the neonatal period and may last an entire lifetime. Babies who are born before they are mature enough to adapt to extrauterine life often require specific care and suffer from complications and chronic health problems. An infant’s immaturity (i.e. how premature he or she is), birth circumstances, and neonatal complications have an impact on the burden of care. 

Four organs are particularly affected: the brain, lungs, digestive system, and ductus arteriosus. Complications include cerebral palsy, intellectual impairment, chronic lung disease, and vision and hearing loss.