Predicting the unpredictable

One of the questions I frequently get asked at antenatal visits (particularly in late pregnancy) is “”When do you think the baby will arrive?” My response is usually “When the baby is ready to arrive.” It would be great if I could accurately predict when a woman would go into labour, how long it would be and when the baby would be born because (a) I could organise my diary around it and never have to reschedule visits again, and (b) I’d probably become very rich as a result. Unfortunately, psychic powers are not something I have been blessed with.