Although animal studies have shown that prenatal alcohol exposure (PAE) is linked to changes in stress-response systems, little is known about the effects of PAE on stress systems in human infants. New findings indicate that the days between conception and pregnancy recognition may be critical for the development of stress-response systems among infants whose mothers consume alcohol.
Results are published in the December issue of Alcoholism: Clinical & Experimental Research.
"Studies on rats and monkeys have shown that the offspring of mothers who drink alcohol during pregnancy develop both elevated and depressed stress hormone responses to challenges," said David W. Haley, assistant professor of psychology at the University of Toronto and the study's corresponding author. In one of the few human studies to look at this issue, he added, stress hormones were elevated both at rest and in response to a physical challenge in the infants when compared to infants whose mothers abstained.
"Stress seems to be mediated through many systems involving neurochemical regulation and hormonal controls," added Sterling K. Clarren, CEO and scientific director of the Canada Northwest FASD Research Network. "Prenatal alcohol exposure seems to play a role in many of these systems, both directly and indirectly, with presumably life long effects. The fact that these alterations are associated with very early gestational exposures is a very important observation for basic understandings of brain development, for public health warnings, and possibly for intervention."
Haley and his colleagues examined the relationships between levels of PAE and infant stress responses. The authors used a modified version of the "still-face procedure" -- an experimental paradigm used to study infant stress and emotion through obtaining measures of the infant's cortisol (stress hormone) levels, heart rate, and negative effect. The infants examined (n=55: 31 males, 24 females) were five to seven months of age, born to mothers who were enrolled in an alcohol-intervention study.
"We found that greater maternal alcohol consumption during pregnancy predicted greater cortisol, autonomic, and emotional responses to social challenge in young infants," said Haley. "Importantly, this was true for infants of mothers who continued to drink after pregnancy recognition as well as for mothers who stopped drinking after pregnancy recognition. These results suggest that the greater the PAE, the greater the activation of the stress-response system. These findings may also indicate that both the time between conception and pregnancy recognition and the time after pregnancy recognition are critical for fetal development."
"The authors are cautious, and should be, in claiming a direct association [among] cortisol levels, heart rate and social observations," said Clarren. "However, the more important fact here is that alcohol does seem to be adversely affecting all of these parameters. The fact that these alterations appear to be caused prior to knowledge of pregnancy -- most likely in the first two months of gestation -- is scientifically interesting because this exposure is occurring before there is any structural differentiation in the cells that will eventually show these aberrations. 'What could alcohol be doing selectively to some germinal cells that presumably does not kill them, but alters their performance after they have multiplied, migrated and matured?' This is a rich area of future study," he said.
"Our findings also show that PAE is associated not only with the infant's response to stress but also with recovery from stress," said Haley. "This is the first time that this has been shown in humans. We also found that while the impact of PAE on stress-hormone responses appears to be the same among boys and girls, heavy alcohol exposure was related to boys showing more impaired or slower recovery compared to girls. In addition, the findings in this study question the current assumption in the field that the effects of PAE are largely limited to the third trimester."
Both Haley and Clarren noted that these findings support caution on the part of women who are planning a pregnancy: abstain from alcohol if at all possible. However, added Clarren, not only are there many unforeseen and unplanned events that may lead to pregnancy, there is also the matter of effectively communicating a message of caution.
"From a public health perspective, how can we effectively warn women to avoid the now-most-common pattern of social drinking -- high binge episodes -- when they are contemplating pregnancy?" he asked. "This is anything but a simple matter."
Alcoholism: Clinical & Experimental Research (ACER) is the official journal of the Research Society on Alcoholism and the International Society for Biomedical Research on Alcoholism. Co-authors of the ACER paper, "Infant Stress Reactivity and Prenatal Alcohol Exposure," were: Nancy S. Handmaker of the Department of Psychology at the University of New Mexico; and Jean Lowe of the Department of Pediatrics at the University of New Mexico. The study was funded by the National Institutes of Health, the National Institute on Alcohol Abuse and Alcoholism, and the National Institute of Mental Health.
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