Doctors have been anecdotally aware of a higher risk with CS for years, but have tended to explain it away because CSs are usually an emergency procedure, caused by a problem with the birth anyway. However, MacDorman's study has removed this confounding factor by analyzing the records only of women who had had no complications whatever with either kind of delivery. This meant that the difference in the babies' death rates could only have been due to the delivery method itself.

In short, caesareans can be lethal-but why?
The risk to the mother can be explained by the fact that it's a major abdominal operation, but why should the baby itself suffer any harm? Well, there is evidence that the baby may sustain "brachial plexus injury, damage to soft tissues, fractures, lacerations, and entrapment of fetal head followed by intracranial haemorrhage" during CS (Cox JP. ICEA Review: Delivery Alternatives in the Term Breech Pregnancy. November, 1988). But those 'complications' are relatively rare, so it's unlikely to be the whole answer.

Natural birth benefits
Another way to explain the new MacDorman data is to turn the question on its head, and ask not what's wrong with CS, but what's so right about a natural birth?

One suggestion is that natural vaginal delivery releases hormones such as prolactin which promote healthy lung functioning. In fact, CS babies are known to have impaired respiration compared with non-CS babies (Arch Dis Child 1997; 77: F237-8). Another factor may be the sheer physical pressure on the baby when being expelled through a narrow opening. This, too, may improve lung function by pushing fluid from the lungs and preparing the child for immediate air-breathing.

Support for these theories has come from studies that have found a link between CS and later respiratory disorders-in particular, asthma. A recent German survey discovered that CS-born children have higher rates of asthma (and, incidentally, more food allergies) up to age two than naturally born babies (Pediatr Allergy Immunol, 2004; 15: 48-54)-a pattern that continues into adulthood. Astonishingly, even as much as a whole generation later, the long-term effects of CS still show up. Finnish researchers have found over three times more cases of asthma in CS-delivered 31-year-olds (J Allergy Clin Immunol, 2001; 107: 732-3).

Osteopaths believe natural labour may have other, less quantifiable effects. Some claim that the compression of the baby's body down the birth canal helps kick-start the natural maturation of infant reflexes, allowing proper neural development to take place. On the other hand, compression of the skull may also cause problems such as colic and irritability.

Avant-garde gynaecologists such as the famous water-birth pioneer Dr Michel Odent are convinced that natural labour has more tangible benefits. Breastfeeding, for example, is often easier after a natural birth, says Odent, possibly because of the better psychological bonding between mother and child after a natural delivery.

There may be two main reasons for this. First, CS is a much more medicalized procedure than a natural birth and, as such, it distances the mother from her newborn. Second, the very act of giving birth through the vagina stimulates the production of oxytocin-dubbed 'the love hormone' by Odent. This hormone is known to play a primary role throughout the whole birthing process, as it floods the mother's brain with powerful signals 'telling her' to care for her infant (Odent M. The Caesarean. London: Free Association Books, 2004).