Caesarean section, also known as C-section, deliveries have been found to not only save lives of mothers when babies are too large to be born naturally—or if there are other health complications—but they also appear to be affecting how humans are evolving, say scientists.
Caesarean birth is the delivery of a baby through a surgical incision in the mother’s abdomen and uterus.
According to a research study, Cliff-edge model of obstetric selection in humans, in the past, larger babies and mothers with narrow pelvis sizes might both have died in labour but today more mothers are needing the procedure to give birth due to their narrow pelvis size.
In turn, it also means that women with ‘at risk’ genes from mothers with narrow pelvises are being carried into future generations as more mums to be are going under the knife.
Historically, women with genes of narrow pelvis would not have been passed from mother to child as both mother and child would have died in labour.
Researchers estimate that cases of babies not fitting down the birth canal have increased from 30 in 1,000 in the 1960s to 36 in 1,000 births today because of this C-section effect, according to estimates from researchers at the University of Vienna in Austria.
Dr Philipp Mitteroecker, of the department of theoretical biology at the University of Vienna, said there was a long standing question in the understanding of human evolution.
“Without modern medical intervention, such problems often were lethal and this is, from an evolutionary perspective, selection”, said Dr Mitteroecker.
“Our intent is not to criticise medical intervention, but it has had an evolutionary effect. Women with a very narrow pelvis would not have survived birth 100 years ago. They do now and pass on their genes encoding for a narrow pelvis to their daughters”, he added.
It is estimated that between three to six per cent of births globally are obstructed because the mother’s pelvis is too small for the head or shoulders of the infant. Over the past 50 or 60 years, this rate has increased to about 3.3-3.6 percent, so up to 36 in 1,000 births.
That is about a 10-20 per cent increase of the original rate, due to the evolutionary effect.
While it may not seem like a big difference, the scientists warn that as the trend continues the number will continue to rise.
It is believed that the size of women’s pelvises and the size of babies’ heads were finely balanced over millions of years of human evolution, with hips unable to dip below a certain width if babies were to survive.
But the increased use of Caesarean sections means all that is changing because women with hips of any size can now give birth to babies of any size.
The report states that Caesareans have minimised the chances of women dying in childbirth, but mothers are passing on the small pelvis genes to their daughters.
Women with a lack of nutrition in their diets tend to be shorter with narrower pelvises, according to the study.
Researchers in Austria say the trend is likely to continue, but not to the extent that non-surgical births will become obsolete. They used a mathematical model to show that increased use of caesareans had accounted for an increase in the size of babies relative to women’s pelvic canals.
The researchers used obstructed childbirth data to reach their estimates using data from the World Health Organization and other large birth studies. They call this “fetopelvic disproportion”.
But the researchers said that more detailed studies would be required to actually confirm the link between C-sections and evolution, as “all we have now is a hypothesis based on the birth data.”
The team admits there may be other factors at work. For example, a change in diet over the generations could also be partly responsible for the mismatch between unborn baby size and pelvis width.
There are problems with the placenta. The placenta grows in your uterus and supplies the baby with food and oxygen through the umbilical cord. Placental problems can cause dangerous bleeding during vaginal birth.
You have an infection, like HIV or genital herpes.
You are having multiples (twins, triplets or more).
You have a chronic health condition, like diabetes or high blood pressure that requires treatment.
Your baby is in a breech position (his bottom or feet are facing down) or a transverse position (his shoulder is facing down). The best position for your baby at birth is head down.
Your baby has problems during labour, like a slow heart rate (also called foetal distress.)
In 2014/2015, National Hospital Insurance Fund (NHIF) indicated it paid out health insurance maternity claims for a total of 61,420 births nationally, with 20,773 (34 per cent) of the new mothers undergoing C-section.
The NHIF Board increased the amount allocated to CS from Sh18,000 to Sh30,000, while that for normal delivery was raised to Sh10,000 from Sh6,000.
Latest data from the World Health Organisation, collected between 2003 and 2011 on Kenya, showed the percentage of CS cases compared to successful natural births rose from 4.3 per cent in 1993 to 5.8 per cent in 2011 with the figures expected to rise significantly further.
In urban areas, CS cases were 2.69 per cent of the total successful births among the urban poor and 11.16 per cent among the urban rich. In addition, CS cases among the rural poor were 3.21 per cent of total live births compared to 9.41 per cent among the rural rich.
