Each extra week in the womb transforms a premature baby's odds
A baby born at 22 weeks has roughly a 6 percent chance of surviving. By 25 weeks that climbs to about 72 percent. Preterm birth, any delivery before 37 weeks, is the leading cause of infant death worldwide, yet estimates suggest most of those deaths could be prevented with inexpensive care.
Full term is about 40 weeks. Doctors grade prematurity by how early it comes: extreme before 28 weeks, very early from 28 to 32, early from 32 to 34 and late from 34 to 36. Late preterm births make up three quarters of the total, while periviable births at 20 to 25 weeks are only about 0.5 percent of deliveries but account for most of the deaths. Around 15 million babies a year arrive early, between 5 and 18 percent of births depending on the country; the UK figure is 7.9 percent and the US 12.3.
Why labour starts early is often a mystery. Researchers point to four well-supported routes: early activation of the fetus's hormone system, an overstretched uterus, bleeding in the uterine lining, and inflammation or infection. Recognised risk factors include diabetes, high blood pressure, carrying twins or more, being very underweight or obese, infections, smoking, air pollution and psychological stress. In the US and UK, Black women have preterm rates of 15 to 18 percent, more than double the white rate, with chronic stress thought to be a major contributor. Filipino Americans also face elevated rates that remain only partly explained, though genetics appears to play a part.
Some interventions have evidence behind them. Progesterone can lower risk for women already at risk, while bed rest has not been shown to help. When delivery threatens between 24 and 37 weeks, corticosteroids may improve outcomes, and drugs such as nifedipine can hold off labour long enough to transfer the mother to a better-equipped hospital and let the steroids act. After birth, care centres on warmth through skin-to-skin contact or incubators, feeding support, infection treatment and help with breathing.
Progress is real but uneven. Deaths from preterm complications fell from 1.57 million in 1990 to 0.81 million in 2015. Of roughly 900,000 preterm deaths in 2019, at least three quarters might have been avoided with cost-effective treatment. Survivors still face higher risks of cerebral palsy, developmental delay and problems with hearing and sight.
Source: Preterm birth
