A new study published in the Proceedings of the National Academy of Sciences has found that a rise in C-sections is causing an increase in head size.

The study was conducted to examine the “puzzle” of obstructed childbirths. Obstructed childbirths occur when the mother’s birth canal cannot accommodate the size of the baby. Researchers explain: “Compared with other primates, human childbirth is difficult because the fetus is large relative to the maternal pelvic canal. It is a long-standing evolutionary puzzle why the pelvis has not evolved to be wider, thus reducing the risk of obstructed labor.” The study found that the rise in C-sections since the 1950s and 1960s has increased incidences of obstructed childbirths and has prompted babies to have larger heads. According to The Independent UK, obstruction is "strikingly high" and now accounts for up to 6 percent of all births worldwide. Lead Author of the study, Dr. Philipp Mitteroecker said that it is not clear what this means for future expectant mothers. "Disproportion may further increase. But I don't think that one day every baby needs to be delivered by C-sections. The selection towards larger babies is limited by the mother's metabolic capacity and also attenuated by modern medical treatment.” Mitteroecker has indicated that the increase in obstruction is simply because women can now survive childbirth where 100 years ago they wouldn’t have. "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 said to the BBC Consultant obstetrician, Daghni Rajasingam was involved in the study and says that the rise in C-sections is attributed to other medical factors. “Things like diabetes are much more common at a younger age so we see many more women of reproductive age who have diabetes. That has consequences as to whether or not they may need a C-section. In addition, the rates of obesity are increasing so more and more women of reproductive age have a higher body mass index and this again has an impact on C-section rates."