Mouse ‘midwives’ help their pregnant companions give birth

Mice appear to help pregnant females when they have difficulty giving birth, and experienced mothers provide the most help. This is believed to be the first official observation of such care in a non-primate, expanding our knowledge of animal care throughout the animal kingdom.

Humans are the only animal known to consistently assist each other during childbirth, which is a particularly lengthy and painful process for humans because our babies have large heads and must navigate relatively narrow birth canals. Other primates such as black snub-nosed monkeys And bonoboshave also been seen helping each other during childbirth, but only occasionally.

Now researchers have observed the same behavior in mice. Robert Froemke of NYU Langone Health in New York and his colleagues noticed this while recording the brain activity of giving birth in mice in a separate study. They found that other mice in the same cage interacted with these animals, and they sometimes seemed to help with the birth of the pups.

To find out more, the researchers genetically modified pregnant mice to lack oxytocin receptors. Oxytocin, often called the “love hormone,” causes uterine contractions that help push baby mice out of the birth canal. Without these cuts, they will likely become stuck and die. The mother also often does not survive.

The researchers placed 10 of these mice in separate cages, pairing each with a female mouse that had previously given birth to at least one litter. A separate group of seven pregnant mice without oxytocin receptors were kept in individual cages.

During childbirth, mother mice helped pregnant mice when their babies became stuck. “She will come up and act like a little mouse midwife and very carefully, with her mouth and paws, pull the puppy out,” says Froemke, who presented the results at a meeting of the Society for Neuroscience in San Diego, California. The helper mice also opened the fluid-filled sac the newborns are in, allowing them to breathe.

Nine out of 10 pregnant mice that were paired with these mouse “midwives” survived birth, and on average, about 90 percent of their litters did, too. In comparison, only one of the single pregnant mice survived birth, and all of the pups in that group died. “There are many reasons why mammals are social, and the main reason is to help each other, especially during these really vulnerable times,” Froemke says. “Even mice struggle with childbirth and childcare just like we do, and can help others, so it's not as traumatic, perhaps about as traumatic as we are.”

To assess whether the presence of a mouse that had previously given birth was required, the team placed 14 more pregnant mice lacking oxytocin receptors in separate cages. Seven of them were paired with male mice, four with female mice that had never given birth, and three with female mice that had not yet given birth but also lacked oxytocin receptors. In addition to their role in uterine contractions, these receptors are thought to important for social interaction.

The researchers found that nearly 60 percent of pregnant mice housed with male mice and half of those housed with female nonmothers survived birth. But these animals did not pull out the puppies during childbirth. Instead, the males would mount the pregnant female, which would apply pressure to her back to help push out the young. Meanwhile, non-mother females groomed the pregnant females and similarly applied pressure to the abdomen. It is not clear why there is a difference in approach between the groups. Among three mice kept with females that lacked oxytocin receptors, only one survived.

However, none of the babies survived this part of the experiment because their fluid-filled sacs remained intact. “It seems that the experience of motherhood is necessary in order to become successful [mouse] midwife,” says Froemke.

The findings support the idea that grooming is more common in the animal kingdom than we thought. For example, mice were seen providing first aid to their unconscious companions. The latest findings suggest that birth and rearing of young are “central organizing forces in animal relationships and social networks,” Froemke says.

“Parental care is one of the most influential social interactions,” says Bianca Jones Marlin at Columbia University in New York. These results highlight that he “requires support.”

Froemke suspects that obstetric-like behavior occurs among wild mice and perhaps other rodents and animals in general. “Giving birth is the most vulnerable time in an animal’s life,” he says. “Animals hide to avoid being found by predators, and I think that's why field observers have rarely observed this in any species other than humans.”