A new study has cast doubt on the idea that women are biologically wired to wake more to a crying baby than men. It suggests that the significant disparity in nighttime care is due to social, rather than biological, factors.
Sometimes termed an “acoustic umbilical cord,” a baby’s cry provides a powerful link to their caregiver, just like the physical umbilical cord was in the womb. Especially in early infancy, crying is a primary mode of communication, designed to elicit a response.
There’s a belief that women are naturally “hardwired” to respond to a crying infant at nighttime, more so than men are. Now, a new study out of Aarhus University in Denmark has challenged that belief – which still doesn’t explain why mothers are far more likely to handle nighttime infant care than fathers are.
“Contrary to popular media portrayals, our male participants did not sleep through baby crying,” said corresponding author Professor Christine Parsons, PhD, from the university’s Department of Clinical Medicine. “We had a lot of variability on how people woke up to the sounds during the experiment, and a lot of overlap between our male and female participants.”
The study aimed to investigate why mothers typically bear a greater share of the nighttime caregiving burden than fathers. Specifically, the researchers investigated whether biological differences in how men and women respond to infant cries at night, before they became parents, might explain this imbalance.
The study consisted of three parts. In Study 1, 140 non-parents (76 women, 64 men) slept at home with a smartphone that played infant cries and alarm sounds at increasing volumes. The researchers recorded when participants woke up in response to the sounds. For Study 2, 117 first-time Danish parent couples were recruited. Each parent reported daily for one week how many times they and their partner got up at night to care for the baby.
From the results of Study 1, the researchers found that women were only slightly, about 14%, more likely to wake up than men when the sounds were played at a very low volume, ranging from 33 to 44 dB. (For context, a whisper is 30 dB; 44 dB would be a very quiet conversation or the background noise in a calm home. By comparison, a baby’s cry can reach 90 dB or more.) There were no significant differences between men and women at louder volumes, and there was no difference in how men and women reacted to cries versus alarms. In other words, women were a bit more sensitive to low-volume sounds, but this difference disappeared once the volume increased.
Regarding Study 2, mothers were three times more likely than fathers to get up at night to care for the baby. Only about 1% of couples had fathers who did more of the nighttime care than mothers. About 23% of couples shared the care equally.
The third part of the study was designed to see if the small differences in waking seen in Study 1 could explain the large gap in nighttime caregiving seen in Study 2. The researchers ran computer simulations, creating virtual couples using the data they’d collected on how easily men and women woke to sounds. These simulated couples experienced typical nights with a baby (about four to five nighttime events per night). If one parent woke up, they “responded” to the baby. If both woke up at the same time, either could be chosen at random. On running these simulations, the researchers found that women ended up doing about 57% of the nighttime care, just slightly more than men. But in the real-world data collected in Study 2, mothers did 76% of the care. None of the 500 simulation runs came close to matching the large gender gap seen in real-life parents.
“The results showed that mothers were three times more likely to handle nighttime infant care than fathers,” said the study’s lead author, PhD student Arnault Quentin-Vermillet. “Our mathematical modeling showed that the large difference in nighttime care cannot be explained by the minor differences we observed in sound sensitivity between men and women.”
While the study has limitations, such as its focus on auditory sensitivity only, the potential for self-reporting bias, and the impact of Danish culture, its findings may have important implications. Principally, they challenge the assumption that women are “naturally” more attuned to infant nighttime needs. The findings also suggest the disparity might be explained by social differences, rather than biological ones.
“We think that there are several factors that explain our results, probably intertwined,” Parsons said. “First, mothers generally take maternity leave before fathers take paternity leave. Mothers then gain more experience in soothing their baby early on than fathers. Second, when mothers are breastfeeding at night, it might make sense for fathers to sleep through.”
The study contributes to a broader conversation about equitable parenting and suggests the structural and societal changes that may be needed to achieve this goal.
The study was published in the journal Emotion.
Source: Aarhus University