Birth normally occurs at a gestational age of 37 to 42 weeks. Childbirth occurring before 37 weeks of gestation is considered preterm; this may happen with a first child. It certainly isn't the case that all first babies are late, many are. However, from the point of view of actually waiting, if you approach the end of your pregnancy expecting your baby to be a couple of weeks late, then you'll avoid the 'sitting around waiting', which can be very frustrating. But remember your body has never done this before and the fact that your ‘due date’ is an estimate and the majority of babies do not arrive on their due date.
NICE (National Institute of Clinical Evidence) published guidelines on induction of labour in 2001 (www.nice.org.uk). If there are no medical or social concerns, women should not be induced before 40 weeks and 12 days 1. NICE suggests alternative practices such as a vaginal sweep before a medical induction.
Sweeping the membranes during a cervical examination is done to bring on labour in women at term. The review of trials found that sweeping brings on labour and is generally safe when there are no other complications 2. Sweeping reduces the need for other methods of labour induction such as oxytocin or prostaglandins.
1 Royal College of Obstetricians and Gynaecologists. Induction of Labour. June 2001. Evidence-based Clinical Guideline Number 9
2 Boulvain M, Stan C, Irion O. Membrane sweeping for induction of labour. Cochrane Database of Systematic Reviews 1997, Issue 4. Art. No.: CD000451. DOI: 10.1002/14651858.CD000451.pub2