One reason premature babies sometimes have to stay in the hospital for a while is that they haven't developed the strength and coordination to nurse properly. Babies who can't feed yet stay in the neonatal intensive care unit (NICU) and rely on a feeding tube.
Doctors and nurses usually give those babies a pacifier whenever possible to help them practice sucking, which can speed up the learning process and shorten their hospital stay.
From previous studies, researchers know that infants also respond well to certain types of music and that their mother's voice can help increase heart and lung stability and growth and improve sleep.
"People are finding out that the influence of parental voice in the NICU is important, so these results are not surprising," said senior author Dr. Nathalie Maitre of Vanderbilt Children's Hospital in Nashville, Tennessee.
"This is yet another example that parents really do make a difference to their babies' development," she said.
The researchers studied about 100 premature babies who had been born between 34 and 36 weeks of development and were relying primarily on a feeding tube (babies are considered full term if they are born between 39 and 41 weeks).
All infants got what babies usually get in the NICU, including pacifiers, skin-to-skin contact whenever possible and gradual introduction to breastfeeding.
Half of the infants also received five daily 15-minute sessions with a special pacifier device that senses when the baby is sucking and plays a recording of the baby's mother singing "Hush Little Baby."
Infants in both groups gained about the same amount of weight during the five-day study, but those with the special pacifiers tended to eat faster when they could. They took in 2 milliliters of fortified breast milk per minute compared to less than 1 milliliter in the comparison group by the end of the study, the researchers reported Monday in Pediatrics.
Infants in the recording group were also able to eat without a feeding tube more often - six and a half times per day versus four times in the comparison group - and ate almost twice as much when they did.
In the pacifier recording group, infants spent an average of 31 days using a feeding tube, compared to 38 days in the non-recording group.
Shorter hospital stays for preemies can have many benefits, said Jayne M. Standley, the inventor of the pacifier-activated music device, called the "PAL," used in the study.
"Premature infants thrive in the home with earlier discharge, parents are relieved to have their babies home from the hospital as soon as possible, and medical costs are greatly reduced," Standley told Reuters Health in an email. "This study has implications to change NICU treatment for feeding problems of premature infants."
Standley, from Florida State University in Tallahassee, didn't participate in the new research.
"We know that newborn infants can recognize their mother's voice because they can hear it in the womb and have ample opportunity to learn what it sounds like," said Amy Needham, who studies infant development at Vanderbilt University.
"Hearing their mother's voice when they suck properly on the pacifier helps them develop proper sucking behavior because the mother's voice acts as a 'reinforcer,'" said Needham, who was not involved in the study.
Maitre had theorized that certain types of carefully chosen music and a mother's voice are both preferred for sucking, and that a tool that uses both might train babies to eat faster.
"It goes back to Pavlov's dog," she said. "It's not romantic, but you can take advantage of behavioral training."
The pacifier device she and her colleagues used measures the pressure and rhythm of sucking. It can't be constructed and needs to be administered by a professional, Maitre said, but it is commercially available and not very expensive. The researchers also had a music therapist select the lullaby, whose melody had to stay within one octave and be very repetitive.
Parents might ask if there is a therapist at the hospital who can help record their voice and play it to their baby, since most therapists can be trained to do this, she said.
Meanwhile, parents should know that spending time talking and singing to their baby can help.
"You can start by singing to your baby. During breastfeeding is a perfect time to do it," Maitre said.