[Ultrasonic assessment of gestational age and prolonged pregnancy].

The benefits of routine use of ultrasound dating of pregnancy have been questioned. With ultrasound dating, the expected date of delivery is often postponed later than calculated. This means that true post-term pregnancies may be undetected and second-trimester determination of gestational age could represent a risk to the infants' health. This possibility has been assessed in a population of ultrasound screened women with optimal conditions for dating the pregnancy by Naegeles rule. No perinatal complications due to undetected post-term pregnancies were found.