Nonlinear analyses of heart rate variability in monochorionic and dichorionic twin fetuses.

ABSTRACT

AIMS: To examine whether the heart rate dynamics of a monochorionic diamniotic (MD) twin fetus is different from a dichorionic diamniotic (DD) twin fetus by nonlinear methods of time series analysis. METHODS: 32 fetal heart rate (FHR) recordings from healthy MD twin fetuses and 58 recordings from healthy DD twin fetuses were used. Nonlinear analyses included attractor reconstruction, calculation of the largest Lyapunov exponents, and estimation of correlation dimension. RESULTS: FHR of healthy twin fetuses was shown to have unique nonlinear characteristics. The largest Lyapunov exponent significantly increased during the pregnancy period. In 30-36 weeks, correlation dimension in MD twins was significantly lower than that in DD twins. In DD twins, we observed a significant increase of correlation dimension from 22-29 to 30-36 weeks. In 22-29 weeks, the difference of the values of correlation dimension in each MD twin pair was significantly lower than that in each DD twin pair. CONCLUSIONS: The heart rate dynamics of healthy MD and DD twin fetuses becomes more chaotic according to gestational age. From the viewpoint of the FHR-regulating system, a pair of MD twins seems to have a more strict binding than a pair of DD twins before 30 weeks' gestation.