Patterns of evoked behaviour in twin pregnancies during the first 22 weeks of gestation.

The objective of this work was to investigate the emergence of intrapair stimulation between twin fetuses and the presence of possible changes in types and percentage of evoked patterns with advancing gestational age. The existence of intrapair stimulation would indicate the functioning of fetal tactile and proprioceptive sensibility. This was studied from video recordings of 30 min ultrasonographic observations of 8 twin pregnancies at 8, 9 and 10 weeks gestational age, of 20 twin pregnancies at 11, 12 and 13 weeks and of 20 twin pregnancies studied with 60 min observations at 15-16, 18-19 and 21-22 weeks. All age groups were subdivided in Monochorionic (Mc) and Dichorionic (Dc) pregnancies. Intrapair stimulation before 11 weeks gestational age is an exceptional event. Due to greater spatial contiguity and thinness of the membrane dividing the two amniotic sacs in Mc pregnancies, it was noted only in these. From 12 weeks onwards, evoked movements began to be observed in Dc pregnancies as well. After the 15th week, intrapair stimulation is a constant and increasing feature of all twin gestations. Movements vary from generalized bodily activity to being progressively localized. No specific evoked movement patterns were observed.