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A recent paper by Barbara Fischer (KLI & University of Vienna), Katharina Pink (Medical University of Vienna) (co-leads) and team reported that female Japanese macaques, despite having the same pelvis-to-fetal-head ratio as female humans, do not suffer the same birth complications as human mothers. This is supported by evidence from a long-term demographic data showing zero maternal mortality linked to childbirth in these non-human primates. This study contributes to our current understanding of the interplay between pelvic morphology and birth dynamics and provides further insights into how to provide better care for human mothers to lessen complications during physiological births. This study was published in the prestigious journal Proceedings of the National Academy of Sciences (PNAS).
In humans, the large size of the fetal head — a consequence of the evolution of large brain size — is often in conflict with the narrow birth canal of the mother, leading to complications during the birth process and is linked to maternal mortality, sometimes as high as 1.5% in countries with poor medical care. An international team of 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) investigated whether such birth complications and maternal mortality also occur in Japanese macaques (Macaca fuscata) which are known to have a similar ratio of pelvis to fetal head as humans. The team used long-term demographic data collected from a population of Japanese macaques residing at Affenberg Landskron, a naturally forested enclosure located in Landskron, Carinthia, Austria. The Affenberg park houses Japanese macaques that have been translocated from Osaka, Japan, since 1996, and now live in a semi-free ranging environment. The data collected over the 27 years (1997-2023 has detailed records of 112 females and the 281 infants born to them, which also confirms that there has been no mortality linked to birth in this population for the last 27 years.
Explaining the low-risk birth in these macaques, the team suggests three mutually non-exclusive hypotheses: (i) The macaque fetal skull is similarly flexible as the human fetal skull. (ii) The macaque pelvis and connective tissue show greater flexibility during birth. (iii) The interplay between macaque pelvic shape and birth dynamics is smoother and incurs fewer complications than in humans. Co-lead author Barbara Fischer explains, “the pelvic girdle and pelvic floor muscles in macaques have greater flexibility during labor compared to humans and the birth dynamics are less restricted due to differences in pelvic morphology”.
There are very few reports on the birthing positions of primates, which presumably make ideal use of the flexibility of the pelvis, which likely contributes to smoother births. The observations from this current study could provide better understanding of the birthing process in humans, and co-lead author and midwife Katharina Pink says, “these observations could inspire future studies to better understand how freedom of movement during physiological birth can lead to more individualized and less invasive care for mothers”.
The study made it to the cover of the journal!