(Reuters Health) - When placed in car seats, babies who are only a week or two premature can have breathing problems similar to those faced by infants born much earlier, a new study suggests.

The majority of preemies are born at 34 to 36 weeks’ gestation, when they’re considered late pre-term, and less at risk for respiratory problems that are common among earlier arrivals with less-developed lungs, researchers note in Pediatrics. The American Academy of Pediatrics recommends screening all preemies to ensure they can sit in the semi-reclining position in car seats without breathing problems, but the study team notes that this test is often overlooked for late pre-term babies.

For the study, researchers examined car seat screening results for 918 late pre-term babies. Overall, 4.6% of these babies failed the test, meaning they could risk potentially fatal breathing difficulties by riding in a car seat.

“Infants who spent time in both the neonatal intensive care unit (NICU) and the newborn nursery had the highest risk of failing, which is important for doctors to know when preparing these babies for discharge home,” said senior study author Dr. Natalie Davis of the University of Maryland School of Medicine in Baltimore.

“Even those who were thought to be the healthiest and did not require the NICU were at risk of unsafe breathing in the car seat,” Davis said by email. “This emphasizes the fact that evaluating late preterm infants for fit and safe breathing in their car seat is important no matter how healthy they appear.”

Pregnancy normally lasts about 40 weeks, and babies born after 37 weeks are considered full-term. In the weeks immediately after birth, preemies often have difficulty breathing and digesting food. Some premature infants also encounter longer-term challenges such as impaired vision, hearing and cognitive skills as well as social and behavioral problems.

In the study, 8.5% of babies who were in both the NICU and the newborn nursery before discharge failed the car seat screening tests.

Among babies who failed these tests, 24% failed two or more assessments. Many of these babies had apnea, a sleep-related breathing disorder, or low oxygen levels; 40% of them required oxygen to be discharged from the hospital.

All babies should be placed in car seats when they ride in a car. But the seats used by most newborns may not work for some late-term preemies because these babies are smaller, weigh less and have immature lungs, brains and hearts, Davis said. Preemies may not breathe effectively for several weeks after birth.

Among other problems, even late-term preemies may be too small to fit properly in car seats, and the straps may hit them in the wrong place on their body and make it harder to breathe, Davis noted. Most car seats are designed for babies who weigh at least five pounds, and may not be safe for babies who weigh less, she added.

Preemies also can have low muscle tone that increases the chance their head will flop from side to side in the car seat or that they will sink or slouch down into an unsafe position that makes it harder for them to breathe, Davis noted.

Parents of preemies should consult with a car seat specialist like a Certified Child Passenger Technician (CPST) to show them how to safely place their baby in the seat and use it in the car, advised Dr. Marilyn Bull, a professor of pediatrics at Indiana University School of Medicine in Indianapolis and author of an editorial accompanying the study.

The Safe Kids Worldwide website has information for parents on proper car seat fit (here: bit.ly/2reuO7Y).

“The take-home message for parents is to follow the recommendations of their physician about when their baby’s breathing is as stable in the car seat as when lying in an open crib,” Bull said by email.

SOURCE: bit.ly/2EGGWkZ Pediatrics, online December 20, 2019.