Read the following passage and questions, then choose the right answer from options, the answer should be one of A, B, C, D.

<passage>:
It's my first go at delivering a baby by caesarean section – and the foetal head is impacted, jammed in its mother's pelvis. To be honest I'm struggling. The clever and sophisticated simulator I'm playing with started life as a lash-up in an obstetrician's home workshop: a Heath Robinson-style contraption barely recognisable as a model of the human body. But it wasn't at that stage intended as a simulator for training medical staff. Its sole purpose was to test the effectiveness of a novel device called a Tydeman tube. Paradoxically, although the testing equipment, Debra, is now commercially available, the device it was intended to test has yet to reach the market. The inventor of the tube and of Desperate Debra is Dr Graham Tydeman, a consultant in obstetrics and gynaecology at Victoria Hospital in Kirkcaldy, Fife. Only after he'd built Debra did he realise that she might serve a purpose beyond his original intention. His is a decade-long tale of inspired insights, thwarted aims and shifting purposes but with a good outcome. Although the Tydeman tube is still in gestation, Desperate Debra herself is now thriving. To understand the desperation of Debra and how the Tydeman tube might help to relieve it requires a brief foray into basic obstetric knowhow.  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. Every year some 160,000 babies are born in the UK this way, with almost two thirds of them classified as emergencies. 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." Which women are most at risk of this setback seems to be largely unpredictable. "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. This could be boosting the frequency of impaction. But, again, no one is certain. If a baby's head is jammed down in the mother's pelvic region, common sense suggests that it might help if a second person gives a gentle backward push on the area of its head visible through the mother's dilated cervix. "In our unit," says Tydeman, "when the woman is fully dilated and you'd expect the baby to come out normally [but it doesn't]… a registrar will be asking for a push-up about one in five times." Although registrars are doctors still in training, they're nonetheless experienced which suggests requests for push-ups during unplanned caesareans are far from uncommon. The Tydeman tube is a gadget intended to make this manoeuvre safer and more effective. So how valuable in training medical staff is a simulator like this? Very, according to Annette Briley. Imagine it's the middle of the night and an unplanned emergency caesarean is required: "Some poor junior doctor might find himself trying to manage it on his own." To have practised the knack of extracting a firmly impacted baby from a simulator is lot better than first honing your skill on a real woman. and to learn where and how hard to push on the infant skull. "Any practice you've done in the cold light of day will help you stay calm and composed in an emergency, and that's what we're aiming for," says Briley. It's still too soon to make a final judgement about Debra’s impact. "When we first brought Debra out," Briley recalls, "some of the really experienced professors said things like, 'We always managed without one. Why would you need this?' But ask them to have a go at using it and then they admit it's really good." Medicine as a whole has an oddly ambivalent relationship to innovation. Some new findings, techniques or equipment take years to penetrate the profession others are seized upon immediately. A proper study of the clinical effectiveness of the Tydeman tube will necessarily involve women giving birth. Assessing the value of Debra as a simulator didn't require human subjects and the team has already conducted such a study. Thirty obstetricians, from three NHS maternity units and with varying levels of experience, took part. They all received a brief explanation of how Debra works, and were then asked to try a timed removal of the foetal head at three different levels of difficulty. Overall, 87 per cent reported that the simulator offered a realistic experience of dealing with an impacted head, and 93 per cent thought it would be valuable as a training device. The use of simulators to teach technical skills is now common in medical schools. You can learn to sew up a knife wound, catheterise a bladder or intubate an airway. You can practise cardiopulmonary resuscitation or ear syringing or even go through the motions of a keyhole surgical procedure. The technology required to do these things may cost a few pounds, or tens of thousands. Either way, given that most of these devices were invented during the past three or four decades, it comes as something of a surprise to learn that simulation for medical purposes can be traced back as far as the Chinese Song dynasty of 960-1279 AD. One of the treatments of choice in that era was, naturally, acupuncture. But how to teach tyro-acupuncturists where to place the needles? Simple. A life-size bronze statue dotted with small holes indicated the points of insertion. And how then to test the students' grasp of their subject? If the statute was hollow, filled with liquid and given an outer coating of wax to mask the holes, a correct needle insertion would be followed by a leak. Given the universality of childbirth it's no surprise that, then as now, the womb turns out to be the most simulated of our organs. For the benefit of 18th-century midwives and doctors-in-training, the Bologna surgeon Giovanni Antonio Galli devised a birthing simulator comprising a glass uterus supported by an artificial pelvis and containing a flexible foetus. Trainees had to deliver the baby while wearing a blindfold. Only the tutor could witness the fumbling of their hands. coup de théâtre , this – a facility for exuding suitably coloured liquids at the appropriate moment. Oddly, as medicine became more scientific, most of these devices fell by the wayside. As an academic review of these and other devices has pointed out, much of the 20th century was something of Dark Ages for simulation. Its value in professional training has had to be rediscovered: an endeavour in which inventive people like Graham Tydeman, sometimes with workshops rich in discarded junk, are still fruitfully engaged. This article was originally published on TheLong+Short. Read the original article.

<question>:
What factor necessitates the change in frequency of performed C-sections?

<options>:
A Uterine environment
B Practitioner training
C Cranial growth
D Advanced technology

<answer>:

C