As a wife of a commercial pilot I asked his opinion on this matter. He says that it is not so much the concern about being "trapped" with an imminent delivery, although this is rather daunting, but they have to consider the possibility of a rapid " de-compression" if the pressurisation system or aircraft structure should fail. This would cause a rapid ( virtually immediate) fall in cabin pressure and terrible consequences to all on board, most of all a pregnant woman. Everyone would suffer ruptured eardrums and epistaxis, for example.They would need to use supplemental O2 and if the pregnant mother was slow to use it what consequences would this have on her unborn child?? Statistically it has been proven that passengers go into " shock" at the sight of O2 masks and require prompting to don them. Also the pressure at cruising altitude (typically 35,000-40,000 feet) would be equivalent to 6,000 feet above sea level in a pressurised airplane. This is a quite a big difference to the pressure on the ground and would increase the risk of rupturing membranes. Just an opinion from someone on the control-end of a plane. Janelle Gridley [log in to unmask]