- Once used to prevent early delivery, alcohol is now recognized as a cause of preterm delivery.
- Alcohol can both inhibit fetal development and precipitate premature delivery.
- The amount, timing and pattern of drinking during pregnancy may determine risk.
- There is likely a "critical period" during pregnancy during which alcohol can induce preterm birth.
Based on animal studies conducted during the 1960s, alcohol was once given to women during the 1970s and even the 1980s to prevent preterm birth. Then researchers discovered fetal risks associated with alcohol consumption, more specifically, fetal alcohol syndrome (FAS) and fetal alcohol effects (FAE). Not until recently, however, have researchers understood that alcohol consumption during pregnancy can actually cause early delivery.
"A lot more attention has been given to the effects of alcohol on the fetus than its effects on the mother," said Jocelynn L. Cook, Post-Doctoral Fellow of Obstetrics and Gynecology at the University of Alberta's Perinatal Research Centre and lead author of a paper recently published in the November edition of Alcoholism: Clinical & Experimental Research. Yet, observed Cook, alcohol can affect the fetus both directly, by restricting its growth, and indirectly through the mother, by prompting early delivery (before 37 weeks of gestation).
"There are two reasons babies can be small," said Robert J. Sokol, Professor of Obstetrics and Gynecology and Director of the C.S. Mott Center for Human Growth and Development at Wayne State University. "One, short gestation or too short a time and two, they grow less well while they're in there. Alcohol is probably associated with both of these. We already knew about growth restriction due to prenatal alcohol exposure, but Dr. Cook's study shows us there's another reason babies are smaller."
Premature or preterm delivery is associated with a number of health consequences, including low birth weight. Low-birthweight infants (weighing about 5.5 pounds) are at higher risk of death or long-term illness and disability (such as respiratory illnesses, impaired postnatal growth and neurodevelopmental problems) than are infants of normal birthweight. The poor performance of the United States in the international ranking of infant mortality rates is mainly due to high rates of premature birth and associated low birth weight, according to the December 1995 issue of the New England Journal of Medicine. These rates have changed little during the past 50 years and may even be on the rise. In fact, according to the Centers for Disease Control and Prevention, preterm births in 1995 increased among white mothers but declined among black mothers to the lowest level since the mid-1980s. In general, however, black women remain almost twice as likely to have a preterm birth as white women do.
Aside from the health consequences of premature delivery, there are also significant economic costs. "Prematurity is the most common cause of admissions into the neonatal intensive care unit," said Dr. Sokol. "Neonates spend tremendous lengths of time in neonatal intensive care units, and these costs add up to a very big hit on the national cost of healthcare."
Cook's study of pregnant mice looked closely at the relationship between alcohol and two factors involved in pregnancy and the process of labor; one is the hormone progesterone and the other is a hormone-like factor called prostaglandin F2a. Researchers already knew that decreased levels of progesterone as well as increased levels of prostaglandins could induce preterm birth in animals. Researchers discovered that alcohol could decrease progesterone and increase prostaglandins. However, Cook and her colleagues also wanted to see what role a recently identified enzyme called prostaglandin H synthase-2 (PGHS-2) might play in alcohol-induced preterm labor.
Cook explained that "if we see that PGHS-2 is going up in both preterm and in normal births, we are closer to understanding the mechanisms, and by understanding the processes of both term and preterm birth we can see how they are different and how they are similar." Indeed, they found that increases in PGHS-2 and prostaglandins were associated with preterm birth induced by alcohol. "What that means," said Cook, "is that we may be able to one day use PGHS-2 inhibitors to prevent preterm birth."
"We still don't know how much alcohol is too much alcohol," said Cook. "It might be different for every woman and every fetus. But there are three main things involved: the amount they consume, the pattern of their drinking, like bingeing, and when they drink during gestation." The third factor was earlier discovered by chance during lab work: Cook and her graduate mentor, Dr. Carrie Randall, found that alcohol induced preterm delivery in mice if administered during a specific, critical 24-hour period (day 16 of a 19-day gestation period). Cook believes a comparable "critical period" may exist in humans.
"We don't know yet when this very critical, narrow window is," said Cook. "But let's say it's a two-week period. We need to figure that out. If women are binge drinking during that two-week period, they're at risk for preterm delivery. We need to get them to cut down on their drinking, at the very least during that critical period."
Sokol agrees. "This is a major public health issue, and the key thing here is prevention," he said. "Prematurity is the largest cause of perinatal morbidity and mortality in the world, including the United States. "It's what kills babies."
Co-authors of the Alcoholism: Clinical & Experimental Research paper included: Dean B. Zaragoza, Perinatal Research Centre, Departments of Obstetrics and Gynaecology, University of Alberta; Nancy M. White and Carrie L. Randall, Alcohol Research Center, Medical University of South Carolina; and David M. Olson, Perinatal Research Centre, Departments of Obstetrics, Gynaecology and Physiology, University of Alberta. The study was funded in part by the National Institute on Alcohol Abuse and Alcoholism, Medical Research Council of Canada, National Sciences and Engineering Research Council of Canada, and the Alberta Heritage Foundation for Medical Research.