Fetal reflex movement in twin pregnancies late in the first trimester: 4-D sonographic study.

The objective of this study was to evaluate reactions to touch in utero between twin fetuses using 4-D sonography late in the first trimester of pregnancy. Six monochorionic diamniotic (MD) and eight dichorionic diamniotic (DD) pregnancies were studied for 30 min with transabdominal 4-D sonography at 12-13 weeks' gestation. The frequencies of no reaction (twins appear to touch each other but there is no clear reaction) and reaction (twins appear to touch each other and there is a clear reaction by the co-twin) movements were evaluated. There was no significant difference in the rate of reaction movements between MD (median, 33.6%) and DD (median, 33.9%) twins. The median rate of reaction movements in all 14 twins was 33.9% (range, 27 to 64.1%). Our findings suggest that the incidence of reflex movement of the co-twin on being touched by the other twin late in the first trimester is more frequent than that assessed by conventional 2-D ultrasound.