Sex Differences in Heart Rate Variability Among Risk-Exposed, Expectant Mothers and Fathers during a Simulated Parenting Stress Protocol

Background: Early parenting represents a normative developmental stage that, although eagerly anticipated, is also experienced as stressful by most parents. Infant crying, in particular, activates the internalized caretaking systems of adults and helps them prepare, physiologically, to parent the distressed infant. Heart and breathing rates increase, the stress hormone cortisol is released, and parents mount a physiological response that supports the activation of a behavioral response to calm the infant. Non-normative physiological responses, such as becoming over- or under-activated, can lead to maladaptive parenting behaviors. Using a sample of risk-exposed (e.g., poverty and violence), expectant (third trimester) parents, the current study examined the physiological response of heart rate variability (HRV) during a simulated stressful parenting protocol. HRV is a measure of the stress response system; low values are associated with higher levels of stress.

Methods: HRV data were continuously collected using MindWare 3000A Wireless System during a stressful parenting task where each expecting parent was individually exposed to a 10 minutes of crying from a lifelike baby doll and asked to “take care of the baby as if it were your own.” RMSSD, which measures beat-to-beat variability and provides a measure of autonomic nervous system arousal, was used in these analyses. The data were grouped into 30-second intervals and then averaged for each epoch to create a baseline, baby cry and recovery score. Multilevel mixed-effects models were estimated in Stata/MP 16 and included an interaction term to evaluate sex differences in physiological responses to the protocol.

Results: The level (intercept) and shape (slope) of the data were markedly different for expectant mothers versus fathers. Mothers demonstrated lower HRV across the entire protocol, compared to fathers. Although their intercepts were different, HRV decreased at approximately the same rate for mothers and fathers at the beginning of the protocol. However, mothers’ HRV began to increase more rapidly as the protocol continued - the slope for mothers increased at a statistically significant rate shortly after the protocol began (B = 0.11, p<0.001), and then leveled off. Fathers, in contrast, demonstrated lower HRV levels for a longer period during the protocol. However, rather than plateauing, fathers HRV increased rapidly toward the end of the protocol ((B = 0.08, p<0.001) and continued to increase during the recovery period.

Conclusion and Implications: Findings suggest that risk-exposed mothers and fathers may mount different physiological responses when exposed to infant crying. Mothers adapted physiologically to the protocol more quickly than fathers, suggesting that they were able to calm down fairly quickly once they engaged in soothing behaviors to calm the baby doll. Fathers, in contrast, became more physiologically activated throughout the protocol, suggesting that that they may have felt less confident in their soothing efforts. These findings inform the development of social work interventions that take a differential approach to work with expectant mothers and fathers. Whereas, mothers may benefit from support and encouragement, fathers may benefit from an educational approach that teaches effective soothing techniques.