Is There a “Dominant Twin” in Utero?

ABSTRACT

A prospective study of 98 pairs of nonstress tests (NSTs) was obtained simultaneously from members of 30 twin gestations. Fifty-five percent of the total fetal heart rate (FHR) accelerations of both twins were associated with each other and occurred within 15 seconds of each other. There were 8.46% synchronous FHR accelerations of both twins, possibly reflecting evoked fetal movements. Statistical analysis failed to reveal evidence of a dominant twin in utero, with one twin initiating the majority of coinciding fetal movements with statistical significance in only three gestations. Examination of combinations of the 30 separate individual significance tests using techniques of meta-analysis demonstrated a p value of 0.81, indicating lack of dominance in any of the 30 pairs of twins. The probability plot, consistent with the large p value for the combination test statistic, suggested that fetal movements in two gestations are related, strengthening the hypothesis of in utero tactile communication between twins. We conclude that the existence of a “dominant twin” in utero cannot be detected by electronic FHR monitoring methods.