A New England Journal of Medicine study reports that cocaine use and tobacco use were associated with miscarriage in a study of 970 adolescents and women from the Philadelphia inner city.
The study reports that pregnant women who:
- Used cocaine (determined through hair analysis) had a 40 percent increase in miscarriage. The result is not statistically significant.
- Smoked (determined through urinalysis) had a statistically significant 80 percent increase in miscarriage.
The study has several major deficiencies:
- Study subjects were inner city adolescents and women -- hardly a "representative" sample.
- It's not too much of a reach -- if at all -- to conclude that inner city conditions and lifestyle could easily explain these weak associations. The study authors acknowledge "Little is known about the influences of lifestyle on spontaneous abortion..."
- Miscarriage is far from understood and flaky associations are easy to come up with. A 1996 American Journal of Epidemiology study (Nov. 15, 1996) reported that:
- Carrying 20-pound loads on the job at least once per day was associated with a statistically significant 70 percent increase in miscarriage.
- Reaching over the shoulders at least once daily was associated with a statistically significant 35 percent increase in miscarriage.
- Drinking 3 or more cups of coffee daily in the first month of pregnancy was associated with a statistically significant 134 percent increase in miscarriage.
Finally, existing studies on smoking and miscarriage have mixed results. Given the weakness in the current study's results, the split in studies is a sign that, in fact, no association exists.
I'm surprised this study didn't spontaneously abort during peer review.
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