 Describe how the frequency of C-sections has changed over time
Incisions have been made in the lower part of the mother's abdomen and womb. I've pushed my gloved hand inside and managed to slide my fingers between the baby's head and the surrounding uterine tissue. She comes with a vulva, a pre-cut incision in her abdomen and, most importantly, a uterus containing a foetal head that should, in the normal way of things, be free to emerge between her legs. Its sole purpose was to test the effectiveness of a novel device called a Tydeman tube. Evolution has endowed us with heads proportionally so large that even when labour runs according to plan, the delivery process involves a bit of a squeeze. For the baby's head to get stuck on the way out may not be usual, but it's by no means a rarity. The standard response is to perform a caesarean section. One audit has suggested that roughly 8,000 babies get stuck and have to be delivered by caesarean at a stage when their mothers are fully dilated. "Some of the babies will be so close to coming out by the normal route," says Tydeman, "that it's then difficult to get them back up and remove them through the hole in the woman's tummy." "We just observe that it happens… It's been discussed in the medical literature since the 1940s, but until 10 years ago, and throughout my training and most of my life as a consultant, it wasn't really talked about." Considering the universality of childbirth, impaction and the best way of dealing with it are topics that seem to have gone remarkably unstudied. "There are strong opinions about why it happens and what to do, but very little research evidence," says Tydeman, adding that many of these opinions are contradictory. In a protracted birth that's destined to end with a caesarean, the longer the labour is allowed to go on before the obstetrician decides to intervene, the greater the likelihood that the baby's head will become impacted. However, concern over the rising number of babies born by caesarean has made doctors more wary of doing them – one consequence of which is that medical staff may allow a difficult birth to continue for longer before they resort to surgery. When obstetricians doing planned caesareans slice open a mother's womb, what they usually see is the baby's head. "When you do a caesarean for an impacted baby," says Tydeman, "you make the incision in the same place, but what you might come across is a shoulder because the baby's so much further down
 The frequency has steadily increased
 The frequency has gradually decreased  The frequency has plateaued  The frequency has no significant trend  The frequency has steadily increased