Evaluation of fetal growth by ultrasonography in twin pregnancy: a comparison between individual and cross-sectional growth curve standards.

Cross sectional curves and individual fetal growth curves standards from the Rossavik growth model [P = c(t)(k + s(t]] were generated for abdominal and head circumferences, femur diaphysis length and estimated fetal weight from a sample of 59 women with twin pregnancy. These curves were compared to their counterparts in singleton pregnancies. Cross sectional curves of the four fetal anatomic parameters under study fell progressively below the curves for singletons during the last trimester of gestation. In contrast, there were few differences between individual fetal groWth curve standards for twin and singleton pregnancies. In 11 of the 59 patients, both methods were used to evaluate fetal growth in the last trimester of gestation. In 5 of these patients, fetal growth was normal by both methods in all 10 fetuses. In the 6 other patients, there were 3 fetuses with abormal estimated fetal weights (EFWs) by both population and individual standards. However, 3 fetuses had abnormal EFW's by populations standards but not by individual standards while the EFW of another fetus was abnormal by individual standards but not by population standards. These results illustrate that the cross-sectional approach to the assessment of growth in twins can be misleading and may lead to incorrect conclusions concerning the growth of these fetuses.