The prevalence of post-term pregnancy (those exceeding 294 days
or 42 weeks of gestation) is about 10% when dating is based on
the first day of the last menstrual period, but this is only
about 5% when dating is by an early ultrasound scan. In about
30% of post-term pregnancies, the fetuses develop a postmaturity
syndrome, characterized by growth restriction, dehydration,
severe desquamation of the epidermis, bile-stained nails and
amnion, advanced hardness of the skull, absence of the vernix
caseosa and lanugo hair. 1: Intrauterine death (black), neonatal
death and post-neonatal death (white) per 1000 ongoing
pregnancies at each gestation. Adapted by permission from Hilder
et al. 1 pregnancy is associated with increased risk of both
intrauterine and postnatal death. Hilder et al. examined 171 527
births in the North East Thames Region in London and reported
that the rate of stillbirth increased six-fold from 0.35 per
1000 ongoing pregnancies at 37 weeks of gestation to 2.12 per
1000 pregnancies at 43 weeks (