Researchers from the National Institute of Child Health and Human
Development (NICHD) and the University of Utah, Salt Lake City, analyzed
stored blood samples from more than 3,000 women, of whom nearly 600 had a
spontaneous abortion. Using a new method to estimate overall caffeine
consumption, the researchers measured blood levels of paraxanthine, a
marker for caffeine consumption. Paraxanthine is a substance produced by
the liver when caffeine is metabolized. It remains in the blood longer than
does caffeine.
Paraxanthine was found in 82 percent of women in both experimental groups.
The mean paraxanthine concentrations were significantly higher in the
miscarriage group than in the control group. However, the risk for
miscarriage is not increased until blood concentrations of paraxanthine are
extremely high.
Very high levels of paraxanthine were fairly rare, occurring in 11 percent
of the miscarriage group and 5 percent of the live-birth group.
"Healthy women with a good pregnancy get a pregnancy signal by the fifth or
sixth week," said Dr. Mark Klebanoff, director of NICHD's division of
epidemiology and primary author of the study. "They are more sensitive to
odors and food flavors, and they don't want to drink coffee first thing in
the morning. Women who miscarry often don't get this pregnancy signal and
continue to consume their normal amounts of coffee."
One factor that complicated this study was that the blood samples had been
stored for more than 30 years. While the long-term stability of
paraxanthine is unknown, the researchers conducted a pilot study that
demonstrated "marked deterioration of paraxanthine was unlikely to have
occurred."
During the 1960s, women were not cautioned against consuming caffeine
during pregnancy, and according to the National Coffee Association, the
national per capita coffee consumed was higher in the 1960s than it is now.
Currently it is very difficult for investigators to recruit a large sample
of women who consume large quantities of caffeine while pregnant.
Since there is no exact way to equate paraxanthine concentration with an
amount of caffeine intake, the study cannot precisely say how much caffeine
is safe during pregnancy.
-The New England Journal of Medicine 1999;22:1639-1644, 1688-1689
Reprinted from Midwifery Today E-News (Vol 2 Issue 10 March 10, 2000)
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