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Postdates Pregnancy
and Fetal Demise
Chapter 9
Kuhali Kundu, DO and
Stephen J. Smith, MD❍ Define post-term pregnancy.
A pregnancy that has extended to or surpassed 42 weeks of gestation or 294 days from the first day of the last
menstrual period.
❍ Name the most common cause of post-term pregnancy.
Error in dating the pregnancy accurately.
❍ What is Naegele Rule?
A method used to calculate the estimated date of confinement. Using the date of the first day of the last menstrual
period as the starting point, subtract 3 months and then add 7 days.
❍ During which trimester is pregnancy dating most accurate?
First trimester.
❍ What is the margin of error for an ultrasound evaluation of pregnancy dating based on gestational age?
The margin of error can be:
- ± 7 days up to 20 weeks of gestation.
- ± 14 days between 20–30 weeks of gestation.
- ± 21 days beyond 30 weeks.
❍ What is the incidence of post-term pregnancy?
Approximately 5 to 10%.