Of the pregnancies ending in spontaneous abortions, those who consumed caffeine amounts of at least 100 mg per day, were more likely to suffer from spontaneous abortions between the 6th and 12th week of pregnancy.In a pregnancy study performed in Sweden, authors collected data from a pregnant population of 1515 pregnant women. Of this population, 953 women held their pregnancies to term and 562 pregnancies resulted in spontaneous abortions. Researchers studied to group via one on one interviewing. The participants were asked about their caffeine intake habits during their pregnancies. Of the pregnancies ending in spontaneous abortions, those who consumed caffeine amounts of at least 100 mg per day, were more likely to suffer from spontaneous abortions between the 6th and 12th week of pregnancy. The more caffeine consumed, the more likely the spontaneous abortion.

The results were adjusted for abnormal fetal karyotype which could increase the chance of spontaneous abortion in pregnancy.

New England Journal of Medicine - December 21, 2000
Authors: Sven Cnattingius, M.D., Ph.D., Lisa B. Signorello, Sc.D., Göran Annerén, M.D., Ph.D., Britt Clausson, M.D., Anders Ekbom, M.D., Ph.D., Elisabeth Ljunger, M.D., William J. Blot, Ph.D., Joseph K. McLaughlin, Ph.D., Gunnar Petersson, B.Sc., Anders Rane, M.D., Ph.D., and Fredrik Granath, Ph.D.