The onset of inter-human contacts: longitudinal ultrasound observations in early twin pregnancies.

Twin pregnancies provide us with the opportunity to observe first reactions towards touch in utero, and this study illustrates the onset and development of these contacts. Forty women with twin pregnancies volunteered to take part in this study, 25 of whom (five monochorionic, 20 dichorionic pairs) fulfilled the inclusion criteria. Between 8 and 12 weeks' gestation, ultrasound examinations were performed transvaginally, and from 13 weeks onwards transabdominally, at weekly intervals. Ultrasound findings were recorded on videotapes and were analyzed retrospectively. The first contacts producing reactions in the co-twin were defined as primary contacts, which could be slow or fast arm/leg/head/body contacts. Primary contacts followed an action-reaction model, and usually lasted < 3 s. These contacts were initially slow and then became fast. The first reactions of the co-twin towards touch were observed at 65 postmenstrual days. Contacts of longer duration between both bodies including extremities, or contacts initiated by sucking movements towards the co-twin were defined as complex contacts and were observed from 85 and 92 post-menstrual days, respectively. Nearly all contacts occurred significantly earlier in monochorionic compared to dichorionic twins. Female/female pairs seemed to develop complex body contacts earlier than male/male pairs, but for the onset of other contacts we have not yet found significant differences between gender combinations.