Certain genes shared between mothers and their babies influence both the size of the mother’s birth canal and the baby’s head, according to an April 11 study by UT and other researchers.
This genetic connection helps reduce the risk of complications during childbirth by ensuring a better physical match between mother and child. This challenges the long-held theory that human evolution caused childbirth difficulties, said Eucharist Kun, fifth-year biochemistry doctoral candidate and co-author of the study.
“The obstetrical dilemma describes an evolutionary trade-off in humans between the need for (a) wide pelvis to safely birth large-brained infants and the need for a narrow pelvis to walk efficiently on two legs,” Kun said in an email. “This compromise results in a birth process that is unusually difficult compared to other primates and may explain why human infants are born relatively underdeveloped, requiring prolonged care.”
Liaoyi Xu, third-year cell and molecular biology doctoral candidate and author of the study, said previous studies exploring the obstetrical dilemma were limited by small sample sizes, which typically ranged from 20 to 200 participants, and biased sampling populations that may not accurately represent the broader population.
In contrast, this research drew on large medical datasets containing information from thousands of mothers and their babies. By applying advanced artificial intelligence tools, the team identified several genetically influenced traits related to pelvic structure, maternal health and infant size, which provided a more comprehensive understanding of the underlying genetic factors affecting those traits.
“To explore the genetic correlation between maternal birth canal size and fetal head size, we first examined how differences in people’s genetics affect their head width as an adult as well as child birth weight (which we used as a proxy for child head width),” Xu said in an email. “Afterwards, we examined the relationship between genetic variants that affect birth canal size with adult/child head width and found a positive association.”
The study discovered that the proportions of the human pelvis are highly heritable, meaning genetic factors play a significant role in determining these traits.
The team also uncovered additional insights into how pelvic size, shaped by genetics, is linked to various health outcomes.
“Larger birth canals were linked to slower walking pace and reduced back pain but increased hip osteoarthritis risk, whereas narrower birth canals were associated with reduced pelvic floor disorder risk but increased obstructed labor risk,” Kun said.
