Individual growth curve standards in twins: growth in the second trimester

To provide a more detailed assessment of the growth of twins, the individual second trimester growth patterns of six fetal parameters [HC, AC, FDL, ThC, head cube (A) and abdominal cube (B)] were studied in fourteen sets of normal twins (six monozygotic and eight dizygotic) and sixteen normal singletons using the Rossavik growth model [P = c(t)(k + s(t)]. Comparisons of start points and coefficient c values indicated no statistically significant differences in the growth processes of twins and singletons in early pregnancy and no detectable effect of zygocity. Comparisons of second trimester growth within sets of twins and randomly paired singletons revealed the presence of differences in feto-placental support. A significant effect of differences in genetic growth potential or maternal support could not be demonstrated, however. These results suggest that with respect to growth, normal twins in the second trimester can be treated as two singletons in the same mother.