HOW ACCURATE IS FETAL BIOMETRY IN THE ASSESSMENT OF FETAL AGE

OBJECTIVE: The purpose of the study was to assess the accuracy of feta l biometry in the midtrimester of pregnancy in the assignment of fetal age. STUDY DESIGN: A total of 152 singleton, 67 twin, and 19 triplet gestations resulting from in vitro fertilization with ultrasonographic fetal biometry from 14 to 22 weeks made up the study population. A ge stational age prediction equation was derived from singletons with the use of stepwise linear regression. This equation was compared with 38 previously published equations and then applied to the twin and tripl er populations. RESULTS: Head circumference was the best predictor of gestational age (random error [SD] 3.77 days). Addition of abdominal c ircumference and femur length to head circumference improved the accur acy of the dating equation (random error 3.35 days). Most dating formu las had systematic errors of <1 week. The systematic error was -0.32 d ay for averaging the singleton-based predictions for twins and -1.26 d ays for triplets. CONCLUSIONS: Gestational age assessment with the use of fetal biometry from 14 to 22 weeks is accurate for singleton, twin , and triplet gestations.