(Reuters Health) - Although extremely preterm birth is no longer the death sentence it once was, the tiniest preemies still have low survival odds and are likely to have severe impairments if they live, a research review suggests.

The team examined data from 65 studies focused on the most vulnerable preemies - those born between 22 and 27 weeks gestation - to see how many survived and how many had severe physical or mental impairments by the time they were 18 to 36 months old.

As a proportion of all deliveries including stillbirths, virtually no babies born at 22 weeks survive. And among only the live births at this very early stage, just 7.3 percent of babies survive. But survival rates surge to 24 percent for the subset of these babies who can be admitted to neonatal intensive care units (NICUs).

In contrast, 82 percent of all babies delivered at 27 weeks live, with the survival odds rising to 90 percent for those admitted to NICUs, the study team reports in Pediatrics.

More time in the womb also increases babies’ odds of survival without severe impairments: at 22 weeks, just 1.2 percent of babies born alive are free of major impairments, but this rises to 64 percent of infants who arrive at 27 weeks.

“Except for infants approaching the limit of viability around 22-24 weeks, most of them survive without major impairments,” said senior study author Dr. Trond Markestad of the University of Bergen in Norway.

“Most major impairments, i.e. cerebral palsy, severe sensory (vision, hearing) impairment and mental retardation are discovered at 3 years of age,” Markestad said by email. “But we know that less severe mental and physical impairments, such as significant learning, behavioral and attention difficulties and clumsiness that are not detected at 3 years are common among school children born very and extremely preterm, and again, in particular when approaching the limit of viability.”

The study only focused on babies born in high-income countries where more mothers might have access to prenatal care and more infants might have access to NICUs and advanced medical technology.

Pregnancy normally lasts about 40 weeks, and babies born after 37 weeks are considered full-term. In the weeks after birth, preemies often have difficulty breathing and digesting food, and their survival odds can depend very much on the availability of effective lung treatments, intravenous nutrition and pumped breast milk.

For the study, researchers focused on babies born between 2000 and 2017. Most advances in breathing and nutrition support happened before this time period.

This may explain why there was little change in survival odds based on when during the study period babies were born, Markestad said.

The smaller studies in the analysis were not designed to prove whether or how preterm births might determine survival odds or the chance of severe impairments. It’s also likely that results would look much different in the developing world.

The NICU makes a big difference, said Dr. Aijaz Farooqi, a pediatrics researcher at Umea University Hospital in Sweden, who wasn’t involved in the study.

“Although survival rates for babies born at 22 and 23 weeks are steadily improving at centers that offer active treatment to these babies, many centers do not offer active treatment,” Farooqi said by email.

“Interventions that might be effective can be started very early in the neonatal intensive care unit (NICU) or nursery, and when possible skin-to skin care is beneficial for both parents and infants,” Farooqi added. “Breast milk and optimal nutrition has shown to be beneficial, and after babies leave the hospital, parents can support development by encouraging movement and play with other kids, as well as by reading and speaking to them often.”

SOURCE: bit.ly/2ToApBr Pediatrics, online January 31, 2019.