Evaluation of obstetric ultrasonography at the first prenatal visit.

A prospective study was performed on 1000 consecutive patients to assess the value of ultrasonography at first prenatal visit. Significant ultrasonographic findings were noted in more than one third of the patients. A discrepancy between ultrasonography and menstrual dating was the most frequently noted abnormality, occurring in 27%; 59% of those would not have been discovered on initial physical examination. Other frequently noted abnormalities included missed abortion (5.7%) and twins (1.6%). The frequency of abnormalities on the initial laboratory studies recommended by the American College of Obstetricians and Gynecologists was evaluated and found to be significantly less than the frequency of clinically important ultrasonographic findings, ranging from 4.0% for positive urine cultures to 0.2% for positive serologic tests. Unexpected findings on physical examination, excluding assessment of pregnancy dating on the basis of uterine size, were even less frequent, occurring in 2.1% of the patients. It is concluded that obstetric ultrasonography at the time of the first prenatal visit is better than physical examination in evaluating the status of the pregnancy and should be considered for all patients.