Coffee drinking can damage your baby even before you get pregnant, according to a Canadian study (JAMA, 22-29 December 1993).
Researchers compared a total of 331 women who had miscarried with 993 who had had normal pregnancies.
After taking into account other variables, like age and social class, they concluded that: "The incidence of fetal loss was strongly associated with caffeine intake during pregnancy, and moderately associated with caffeine loss before pregnancy."
The study suggests that even a moderate consumption of caffeine during the first trimester around one and a half cups of coffee a day can lead to a doubled risk of spontaneous abortion.
Furthermore, high caffeine consumption in the month before pregnancy "nearly doubled the risk" of miscarriage.
The Canadian study found that caffeine has a more harmful effect at lower levels than suggested by the findings of earlier research. Nevertheless, an editorial in the same edition of the journal pointed out: "Nutritional status was not measured in either study and this might modify susceptibility to the harmful effects of caffeine."
The editorial noted that a larger proportion of women in the Canadian study smoked, which may increase the toxic effects of caffeine on the baby.
It added, however, that smoking was taken into account in the study. "No interaction of caffeine and smoking was found," they said.