Intrauterine growth of twins judged by BPD measurements.

Both earlier growth charts of twins composed of birth weight at different gestational ages and recent reports on twin biparietal diameter (BPD) growth, indicate that twins' growth is less than that of singletons during the later period of gestation. In the present study, growth curves are constructed separately for the first and the second twin from 489 paired ultrasonic BPD measurements of 119 twin pregnancies. The distribution of BPD values in twins was found to be slightly wider than our normal range curve for singletons. The mean BPD values of twins were close to those of singletons in the second trimester. From the 32nd week on, the twins' mean weekly BPD increment decreased, this lesser growth rate being more marked than that of singletons. The second twin's BPD growth curve ran consistently below that of the first. Our results agree with the earlier findings that the growth of twins is retarded during the later part of pregnancy. They point to different BPD growth patterns between the first and the second twin.