Although the study did not report any negative effects on fetal health, the findings confirm that emotion-based changes in a woman's cardiovascular activity can have "real-time" effects on a fetus, say Catherine Monk, Ph.D., of Columbia University and colleagues.
Previous studies show that stress during pregnancy can increase the risk of low-birth weight and premature births, but a growing body of evidence also suggests that pregnancy stress may "re-program" the fetal environment in ways that affect the baby's behavior and functioning later in life, according to the researchers.
More analysis is needed to determine whether the heart rate effects in the current study "have implications for the child's fetal and long-term health and development," Monk and colleagues say.
The researchers collected data on the heart rate, blood pressure and breathing rate of 32 healthy women in their third trimester before, during and after a short psychological test designed to produce a stress response. Monk and colleagues monitored fetal heart rate simultaneously. The women also completed a questionnaire that measured their everyday levels of anxiety.
Increases in fetal heart rate during the stress test were related to the mother's overall level of anxiety, but not related to the mother's own elevated heart rate and blood pressure during the test, the researchers found.
However, mothers' cardiovascular activity and their general anxiety level were both highly associated with changes in fetal heart rate during the "recovery" period after the stress test was completed.
"As women recovered from the stress-eliciting task, fetuses of more highly anxious women showed greater heart rate decreases," Monk says.
The researchers are uncertain why fetal heart rate changes are associated with the mother's heart rate and blood pressure activity during recovery and not during the stress test, but suggest that it may take time for the physiological effects of stress to reach the fetus.
"On the other hand, the relationship between fetal heart rate activity and a woman's daily anxiety levels may suggest that fetal heart rate patterns have already been shaped by a woman's mood during the previous months of pregnancy," Monk says.
The study is published in the February issue of Developmental and Behavioral Pediatrics and was supported in part by the Sackler Institute Award, the March of Dimes and the National Alliance for Research on Schizophrenia and Depression.
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