Coffee and Pregnancy Mix Safely

AARHUS, Denmark, Jan. 26 -- Pregnant women can drink coffee without the fear it will lead to a premature birth or a low-birth-weight baby, according to researchers here.

In a randomized double-blind study of more than 1,000 pregnant women, there was no evidence that the caffeine in three cups a day had any effect on the outcome of the pregnancy, found Bodil Hammer Bech, Ph.D., of the Institute of Public Health at the University of Aarhus.

On the other hand, the results were not as good for women who combined caffeinated coffee with cigarettes, a one-two punch that increased the risk of smaller babies, Dr. Bech and colleagues reported online in the BMJ. There was no such effect for smokers who drank decaffeinated coffee.

Some previous research has suggested that a high caffeine intake can lower birth weights by as much as 200 grams, while other studies have found no effect, the researchers noted. A similar confusion has been seen in studies looking at caffeine and the risk of a low-birth-weight baby, defined as a full-term infant weighing less than 2,500 grams.

"These conflicting results have puzzled public health authorities, and in some countries pregnant women are warned against caffeine consumption," Dr. Bech and colleagues said.

Women with a high caffeine intake during pregnancy tend to smoke more, to drink more alcohol, and to have a lower level of education, the researcher noted. Outside a randomized controlled study, these confounding factors are difficult to control.

Between April 1996 and April 1998, Dr. Bech and colleagues enrolled 1,207 healthy women who drank more than three cups of coffee a day -- seen as a high caffeine intake -- and who were less than twenty weeks pregnant.

They were randomized to get a supply of instant coffee, either with or without caffeine, and their caffeine intake from other sources -- such as tea or soft drinks -- was monitored through interviews.

On average, the women getting caffeinated coffee had a daily intake of 317 mg/day, compared to 117 mg/day for those getting decaffeinated coffee, the researchers found.

After adjustment for length of gestation, parity, pre-pregnancy body mass index, and smoking at study entry, analysis of the infants at birth found:

• The mean birth weight of babies born to women in the decaffeinated group was 16 grams lower than those born to women in the caffeinated group.
• The decaffeinated group had a gestation length that was 1.31 days shorter on average than women in the caffeinated group.
• Neither difference was statistically significant.

In the caffeinated group, 4.2% of infants were born prematurely and 4.5% were small for their gestational age, compared to 5.2% premature births and 4.7% low-birth-weight babies in the decaffeinated groups.

On the other hand, smoking and drinking caffeinated coffee seemed to have an effect: Women who smoked more than 10 cigarettes a day at study entry and were randomized to the caffeine arm had babies that were on average 263 grams lighter than those born to smokers on decaffeinated coffee. The difference was statistically significant at P=0.002.

The finding means that "care should be taken when extrapolating (the overall) results to smokers," the researchers said.

Dr. Bech and colleagues noted that women in the study were in the second half of pregnancy, so that "if caffeine has an effect on birth weight by mechanisms that only operates early in pregnancy we would not detect it."

It is also possible that substances in coffee other than caffeine may influence birth weight, they said.