Brian Monson, a professor of speech and hearing sciences at the University of Illinois Urbana-Champaign, said that premature babies are exposed to a completely different soundscape than fetuses that remain in the womb for the full term of pregnancy, along with other challenges that come with prematurity. who led the study with researchers and clinicians at Carle Foundation Hospital in Urbana. The research will help clinicians develop ways to expose premature babies to sound more like fetuses, he said.
“The intrauterine environment is unique, transmitting constant, primarily low-frequency sounds and sounds from the mother’s cardiovascular and digestive systems to the fetal ear through the amniotic fluid,” the researchers write. “There are also sounds of other people nearby, music and other atmospheric sounds that affect the mother’s womb.”
Conversely, infants in hospital neonatal intensive care units are often exposed to a variety of electronic and mechanical sounds, including alarms. They are exposed to language, but only when nurses or parents talk nearby. Prior to this study, evidence and anecdotal observations suggested that premature babies heard less language during the day than their counterparts in the womb.
Tracking Young Infant Exposure to Voices and Voices
Previous studies have only skimmed the differences, Monson said. For example, some collected sound exposure data at only a few time points during a preterm infant’s NICU stay. Some studies have compared exposures of full-term neonates to preterm infants rather than tracking exposures in utero to capture the same developmental window in each group.
Previous research has found that premature babies who spend several weeks in hospital NICUs often lag behind age-matched full-term babies in language learning and other neurodevelopmental milestones. Hearing begins in the fetus at 23 weeks of pregnancy, says Monson. Late in pregnancy, a fetus with healthy hearing will begin to recognize its mother’s voice or language.
In the new study, Monson and colleagues analyzed more than 23,000 hours of auditory exposure data collected from 27 typically developing fetuses and 24 premature infants. The study collected fetal “extra-fetal” sound exposures by asking mothers to wear 24-hour voice recording devices twice a week for up to 14 weeks in the third trimester of pregnancy. The team also recorded 24-hour NICU sound exposure data three times per week for each preterm infant in the study.
Using an automated algorithm, the researchers analyzed the data to look for differences in the rates and types of sound exposure experienced by fetuses in utero and premature infants in the NICU.
“We found a five-fold increase in exposure to tongue-in-cheek per day for fetuses compared to preterm infants,” Monson said. “That’s an exciting difference for me.”
The two groups also differed in the amount of silence and noise they heard, and the duration of that sound exposure. Deprived of sounds normally heard in the womb, “very premature babies also remain silent for long periods of time, which never happens in the womb,” the researchers found.
“Replacing the language exposure were sounds like mechanical noises and alarms from major equipment in the NICU,” Monson said.
Healthy voices, healthy brains
For NICU infants, sound exposures are evenly distributed over a 24-hour period, whereas fetuses experience a more pronounced day/night cycle of sounds. Overcoming this difference could allow premature babies to develop a healthy circadian rhythm, Monson said. .
“This is a period of life where the auditory nervous system waits for healthy sound exposures to mature properly,” Monson said. “These differences can have adverse effects on these young babies and their developing brains.”