Association of in utero behavioral patterns of twins with each other as indicated by fetal heart rate reactivity and nonreactivity.

Prospective analysis of 75 pairs of nonstress tests (NSTs) obtained simultaneously from both members of 35 twin gestations was performed to quantitatively assess the incidence of simultaneous periods of fetal heart rate (FHR) reactivity and nonreactivity of twins. Comparative analysis of the paired NSTs was used to compute rates of simultaneous fetal heart rate reactivity and nonreactivity. Statistical analysis involved comparison of weighted averages of these rates, using sequence lengths as weights. Weighted standard deviations were used to describe variability between sets of NSTs. Trend analysis was performed using weighted linear regression to calculate slopes for pairs of twins with three or more repeat NSTs. Groups of twins were compared by performing a variance stabilizing transformation on the appropriate rates, and using a two sample t test to compare the means of transformed data. Analysis of this data revealed that twins exhibited similar in utero fetal heart reactivity and nonreactivity as indicated by simultaneous electronic fetal monitoring during 79.90% +/- 1.62 (SD) of the time monitored. The incidence of periods of simultaneously reactive FHR and simultaneously nonreactive FHR were 11.79% +/- 1.02 and 68.10% +/- 2.17, respectively, irrespective of gestational age. These data confirm the hypothesis that periods of FHR reactivity and nonreactivity of twins are strongly associated with each other.