We studied the effects of caffeine ingestion during pregnancy. A total number of 9,921 healthy pregnant women with a gestational age after 24 weeks were subjected to the study. The women who drank more than 5 cups of coffee per day had a high incidence of impending abortion, premature labor, and fetuses small for gestational age. The heavy coffee drinkers among the pregnant women had high rates of spontaneous abortion, chromosomal abnormality and congenital multi-anomalies. However, we would like to stress that the multiple socioeconomic variables might be more important than any direct effect of caffeine.