A female Japanese macaque nursing her few days old infant. Japanese macaques, also known as snow monkeys, give birth in spring to early summer. This early summer birthing season allows the infant to grow up and become strong enough by winter to survive the cold months. Credit: Angela Stojan. CC BY.
New research shows that Japanese macaques give birth more easily than women with no maternal mortality at birth.
An international research team led by the University of Vienna and the Medical University of Vienna has used long-term demographic data from Japanese macaques – a monkey species within the family of Old World monkeys – to show that, unlike humans, there is no maternal mortality in these primates linked to childbirth, despite the same pelvis-to-head ratio.
The evolution of large brains and associated large foetal heads are key factors linked to maternal mortality in primates during childbirth.
For humans, the baby’s large head in relation to the mother’s narrow birth canal can lead to serious birth complications.
In countries with poor medical care, up to 1.5% of mothers die in childbirth as a consequence of birth.
Macaques have a similar pelvis-to-foetal head ratio to humans. However, it remains unknown whether they face similar birth complications and maternal mortality as humans.
Biologists and midwives from the University of Vienna, the Medical University of Vienna, the Konrad Lorenz Institute for Evolution and Cognition Research (Klosterneuburg) and Kyoto University (Japan) have now investigated whether this is the case.
Their research was based on long-term demographic data of birth and death events collected from a semi-free-living Japanese macaque population housed at the Affenberg in Landskron, Carinthia, Austria.
During the 27-year study period, 281 infants were born to 112 female macaques. The semi-free environment at Affenberg offers scientists the opportunity to study the behaviour and reproduction of Japanese macaques under near-natural conditions.
A female Japanese macaque nursing her six-month-old infant in winter. Japanese macaques, also known as snow monkeys, give birth to their infants between spring and early summer so that they are strong enough to survive the cold winter months. Credit: Angela Stojan. CC BY.
No maternal mortality in macaques
Co-first author Katharina Pink, a midwife and evolutionary anthropologist from the Department of Obstetrics and Feto-Maternal Medicine at the Medical University of Vienna, said: “We were able to show for this population that not a single female has died in connection with the birth of her young within the last 27 years.”
This result shows that Japanese macaques do not face the same risk of maternal mortality as humans, despite having a similarly narrow pelvis-to-head ratio.
Why childbirth appears to be less risky in macaques compared to humans remains an open question.
Co-first author Barbara Fischer, a scientist at the Department of Evolutionary Biology at the University of Vienna and the Konrad Lorenz Institute for Evolution and Cognition Research, said: “We think that the pelvic girdle and pelvic floor muscles in macaques have greater flexibility during labour compared to humans and that the birth dynamics are less restricted due to differences in pelvic morphology,”
Only very few scientific reports on births of free-living, non-human primates exist so far. Most of these births take place during the night or in the early hours of the morning and are therefore difficult to observe.
Birth events that have been described show that non-human primates intuitively prefer standing or squatting birthing positions and thus presumably make ideal use of the flexibility of the pelvis.
Pink said: “These observations could inspire future studies to better understand how freedom of movement during physiological birth can lead to more individualised and less invasive care for mothers.”
The results of the study were published in PNAS.
