Clinical measures of gestational age in normal pregnancies.

Obstetric findings in 89 healthy women were evaluated prospectively by one obstetrician unaware of menstrual history. With weekly examinations, fetal heart tones were audible by fetoscope at 17.1 +/- 1.1 weeks' gestation (mean +/- SD) and the fundus reached the umbilicus at 16.6 +/- 0.9 weeks. At 20 to 31 weeks, fundal height in centimeters equaled weeks' gestation (confidence interval: +/- 3 weeks). The accuracy of predicting delivery date from combined findings (SD: 11.4 days) approached that from reliable menstrual history (SD: 10.2 days). Gestational age at delivery minus the pediatric Dubowitz estimate was 0.4 +/- 1.7 weeks. Gestational age may be overestimated by up to six weeks by assuming that the fundus reaches the umbilicus or that fetal heart tones appear at 20 weeks. However, carefully derived obstetric estimates potentially may be more reliable than pediatric estimates.