Fetal behaviour: a commentary

Physiological reactivity of pregnant women to evoked fetal startle

OBJECTIVE

The bidirectional nature of mother-child interaction is widely acknowledged during infancy and childhood. Prevailing models during pregnancy focus on unidirectional influences exerted by the pregnant woman on the developing fetus. Prior work has indicated that the fetus also affects the pregnant woman. Our objective was to determine whether a maternal psychophysiological response to stimulation of the fetus could be isolated.

METHODS

Using a longitudinal design, an airborne auditory stimulus was used to elicit a fetal heart rate and motor response at 24 (n=47) and 36 weeks (n=45) of gestation. Women were blind to condition (stimulus versus sham). Maternal parameters included cardiac (heart rate) and electrodermal (skin conductance) responses. Multilevel modeling of repeated measures with 5 data points per second was used to examine fetal and maternal responses.

RESULTS

As expected, compared to a sham condition, the stimulus generated a fetal motor response at both gestational ages, consistent with a mild fetal startle. Fetal stimulation was associated with significant, transient slowing of maternal heart rate coupled with increased skin conductance within 10s of the stimulus at both gestational ages. Nulliparous women showed greater electrodermal responsiveness. The magnitude of the fetal motor response significantly corresponded to the maternal skin conductance response at 5, 10, 15, and 30s following stimulation.

CONCLUSION

Elicited fetal movement exerts an independent influence on the maternal autonomic nervous system. This finding contributes to current models of the dyadic relationship during pregnancy between fetus and pregnant woman.

Accelerometer-based fetal movement detection

Monitoring fetal wellbeing is a compelling problem in modern obstetrics. Clinicians have become increasingly aware of the link between fetal activity (movement), well-being, and later developmental outcome. We have recently developed an ambulatory accelerometer-based fetal activity monitor (AFAM) to record 24-hour fetal movement. Using this system, we aim at developing signal processing methods to automatically detect and quantitatively characterize fetal movements. The first step in this direction is to test the performance of the accelerometer in detecting fetal movement against real-time ultrasound imaging (taken as the gold standard). This paper reports first results of this performance analysis.

Psychological and psychophysiological considerations regarding the maternal-fetal relationship

The earliest relationship does not begin with birth. Pregnant women construct mental representations of the fetus, and feelings of affiliation or "maternal-fetal attachment" generally increase over the course of gestation. While there is a fairly substantial literature on the development and moderation of psychological features of the maternal-fetal relationship, including the role of ultrasound imaging, relatively little is known about the manner in which maternal psychological functioning influences the fetus. Dispositional levels of maternal stress and anxiety are modestly associated with aspects of fetal heart rate and motor activity. Both induced maternal arousal and relaxation generate fairly immediate alterations to fetal neurobehaviors; the most consistently observed fetal response to changes in maternal psychological state involves suppression of motor activity. These effects may be mediated, in part, by an orienting response of the fetus to changes in the intrauterine environment. Conversely, there is evidence that fetal behaviors elicit maternal physiological responses. Integration of this finding into a more dynamic model of the maternal-fetal dyad, and implications for the postnatal relationship are discussed. Research on the period before birth affords tremendous opportunity for developmental scientists to advance understanding of the origins of human attachment.

Prenatal development of intrafetal and maternal-fetal synchrony

Fetal and maternal data were monitored serially at 6 gestational ages from 20 to 38 weeks in 195 Peruvian fetuses. Digitized data included fetal heart rate and motor activity, as well as maternal heart rate and electrodermal conductance. Time series analysis evaluated the development of synchrony in 2 streams of fetal functioning and between mothers and fetuses. Intrafetal synchrony between heart rate and motor activity developed in an orderly fashion, with peak cross-correlation approaching an asymptote at 5 s at 28 weeks. Synchrony was not observed between fetal heart rate and maternal measures. Fetal motor activity exhibited synchrony with both maternal electrodermal and heart rate activity. Implications for revealing fundamental properties of neural development prior to birth are discussed.

Fetal heart rate and variability: stability and prediction to developmental outcomes in early childhood

Stability in cardiac indicators before birth and their utility in predicting variation in postnatal development were examined. Fetal heart rate and variability were measured longitudinally from 20 through 38 weeks gestation (n = 137) and again at age 2 (n = 79). Significant within-individual stability during the prenatal period and into childhood was demonstrated. Fetal heart rate variability at or after 28 weeks gestation and steeper developmental trajectories were significantly associated with mental and psychomotor development at 2 years (n = 82) and language ability at 2.5 years (n = 61). These data suggest that the foundations of individual differences in autonomic control originate during gestation and the developmental momentum of the fetal period continues after birth.

Neurobehavioral assessment before birth

The complexities of neurobehavioral assessment of the fetus, which can be neither directly viewed nor manipulated, cannot be understated. Impetus to develop methods for measuring fetal neurobehavioral development has been provided by the recognition that individual differences in neurobehavioral functioning do not originate with birth and acceptance of the key contribution of the antenatal period to postnatal life. Research has centered around four aspects of fetal functioning: heart rate, motor activity, behavioral state, and responsivity to stimulation. Longitudinal studies have revealed that the developmental trajectories of these characteristics parallel the developing nervous system, detected a transitional period between 28 and 32 weeks gestation, and established within-fetal stability during the second half of gestation. Despite the promise of fetal stimulation and habituation paradigms as measures of neural functioning, significant safety and ethical concerns exist. Construction of a unified fetal neurobehavioral scale is premature until a sufficient degree of normative data is available and the predictive validity of specific aspects of fetal neurobehavior to child developmental outcomes is better established.