Mothers pass on caesarean section risk to their daughters
Girls who were born by caesarean section are later more likely to give birth to their child in this way than those who were born naturally. Researchers from Austria have now calculated this.
How the expectant mother was born
A few years ago it was reported that there are more and more Caesarean section births and almost every third birth in Germany takes place in this way, but now the numbers in this country have decreased slightly. According to experts, the rate should be reduced even further, because "every caesarean section is an operation and should only be performed if it is medically necessary," said the German Midwifery Association (DHV) in a message. Whether a caesarean section is necessary obviously also depends on how the mother-to-be was born.
Evolutionary anatomical change
Women who were born with a caesarean section because of a mother's cranial pelvic mismatch are more than twice as likely to have a miscarriage at birth than their women who were born naturally.
This is the conclusion reached by evolutionary biologists from the University of Vienna around Philipp Mitteröcker, who explain in a mathematical model the apparently paradoxical phenomenon that the rate of birth problems could not be reduced by natural selection, according to a statement.
The data also support the thesis that the regular use of caesarean sections has already led to an evolutionary anatomical change. Your calculations currently appear in the "PNAS" magazine.
Number of Caesarean sections multiplied
In most countries, the number of caesarean sections has multiplied over the past few decades, making the caesarean section (Latin for caesarean section) one of the most frequently performed operations today.
Experts believe that this is a social phenomenon, since the rate of actual birth problems - above all the so-called "pelvis-head mismatch" (note: the child's head does not fit through the birth canal) - is many times lower.
Philipp Mitteröcker from the Department of Theoretical Biology at the University of Vienna asked himself why evolution did not lead to a larger birth canal and thus to safer births.
Baby's chances of survival
In a study from 2016, the evolutionary biologist explained this apparently paradoxical situation with a population-genetic-mathematical model as a kind of "fitness dilemma".
"From an evolutionary point of view, a narrow pelvis is an advantage: on the one hand for our locomotion, but also because in very wide pelvises, uterine prolapse and other pelvic floor problems can occur at birth," says Mitteröcker.
On the other hand, a baby's chances of survival increase the larger it is at birth. So here the selection pressure towards narrower pools and that towards larger babies, so to speak, get in the way.
"For our fitness curve, this means that the narrower the pelvis and the bigger the child, the better - but only to the point where the child no longer fits: Then it becomes abruptly fatal," explained the expert.
Birth problems due to a skull and pelvis disparity
Due to this unusual selection process, the rate of birth problems cannot be reduced through natural selection. Furthermore, the researchers were able to show through their model that the regular use of life-saving Caesarean sections in the past 50 to 60 years has already brought about an evolutionary change in anatomical dimensions.
This in turn has increased the incidence of birth problems from a skull and pelvic disproportion by ten to 20 percent.
However, this predicted increase in cranial-pelvic mismatches can hardly be proven empirically, since such a mismatch is very difficult to diagnose.
The Caesarean section rate as an indirect measure has in turn increased significantly more due to many other, also non-medical reasons.
"The increase in caesarean sections is a social phenomenon, but not only: the birth problems have also increased, albeit to a much lesser extent than the caesarean sections," said Mitteröcker.
Birth problems and cesarean section examined over two generations
In the current PNAS study, the scientists are now showing that the "cliff edge model" also predicts that women who were born due to caesarean section due to cranial-pelvic mismatch are more than twice as likely to have a mismatch at birth of their children develop as women who were born naturally.
This significant effect should be easier to see in epidemiological data than the evolutionary increase.
“In fact, we found empirical studies that looked at birth problems and cesarean sections over two generations. The predicted ‘heredity’ of cranial-pelvic mismatch and caesarean section is surprisingly precisely confirmed by these studies, ”said Mitteröcker.
This theoretical prediction of a complex epidemiological pattern also provides independent confirmation of the “cliff edge model” and its evolutionary implication. (ad)