ABSTRACT
Using first trimester fetal crown-rump length (CRL) measurements as the criterion
for gestational dating, rather than menstrual history or neonatal gestational age
evaluation afterbirth, may be a more accurate way of evaluating the accuracy of second
or third trimester ultrasonic measurements for gestational age estimation. This hypothesis
was tested using two study groups to evaluate the accuracy of second or third trimester
ultrasound measurements for the estimation of gestational age. Three hundred twenty
normal obstetric patients who had first trimester CRL measurements were evaluated
in the first study. Stepwise multiple regression analysis was used to determine the
best combination of multiple ultrasonic parameters for calculation of gestational
age, using each patient's CRL as his or her own control. The best formula derived
from the first set of patients was used in a second set of 138 high-risk patients
to determine the accuracy of multiple ultrasonic parameters obtained during the second
or third trimester to date gestation accurately. The analysis confirmed the accuracy
of multiple ultrasonic parameters for gestational dating and indicated that the use
of two parameters (head circumference and femur length) was as accurate as the traditional
four-parameter technique.
Keywords
Ultrasound - obstetric - gestational age
