Among the earliest volumes of this monograph series was a report by
Lester Sontag and colleagues, of the esteemed Fels Institute, on the
heart rate of the human fetus as an expression of the developing nervous
system. Here, some 75 years later, we commemorate this work and provide
historical and contemporary context on knowledge regarding fetal
development, as well as results from our own research. These are based
on synchronized monitoring of maternal and fetal parameters assessed
between 24 and 36 weeks gestation on 740 maternal-fetal pairs compiled
from eight separate longitudinal studies, which commenced in the early
1990s. Data include maternal heart rate, respiratory sinus arrhythmia,
and electrodermal activity and fetal heart rate, motor activity, and
their integration. Hierarchical linear modeling of developmental
trajectories reveals that the fetus develops in predictable ways
consistent with advancing parasympathetic regulation. Findings also
include: within-fetus stability (i.e., preservation of rank ordering
over time) for heart rate, motor, and coupling measures; a transitional
period of decelerating development near 30 weeks gestation; sex
differences in fetal heart rate measures but not in most fetal motor
activity measures; modest correspondence in fetal neurodevelopment among
siblings as compared to unrelated fetuses; and deviations from normative
fetal development in fetuses affected by intrauterine growth restriction
and other conditions. Maternal parameters also change during this period
of gestation and there is evidence that fetal sex and individual
variation in fetal neurobehavior infl uence maternal physiological
processes and the local intrauterine context. Results are discussed
within the framework of neuromaturation, the emergence of individual
differences, and the bidirectional nature of the maternal-fetal
relationship. We pose a number of open questions for future research.
Although the human fetus remains just out of reach, new technologies
portend an era of accelerated discovery of the earliest period of
development.