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Coffee During Pregnancy

Updated November 20th, 2010

Is it wise to drink coffee while you are pregnant? The question of coffee drinking safety during pregnancy causes many disagreements. Doctors are split on what this means for pregnant women, with some advising avoiding coffee altogether and others saying it is still safe in moderation.

And though a lot is not clear in the question of coffee safety, it is authentically known, that:

  • Caffeine readily crosses the placental barrier.
  • Clearance of caffeine is slower in pregnant vs non pregnant women.
  • The fetus has low levels of enzymes which break down caffeine, so fetal metabolism of caffeine is delayed.

1 Whence all has begun

In 1980, the FDA published recommendations that advised pregnant women to avoid or limit caffeine. The advice stemmed from the study with rats, conducted by FDA scientists. The study found that one of every five baby rats born to mothers that had been force-fed caffeine while they were pregnant had permanent birth defects – mainly missing or incomplete toes – and delayed development of bones, particularly of the breastbone.

However, subsequent studies have not identified an association between congenital malformations and caffeine consumption in women. Also, rodents are generally more susceptible to teratogenic influences than humans. Differences exist between rodents and humans regarding caffeine metabolism, and the doses used in the rat study were excessively higher than normal. A 60-kg human would have to consume approximately 50 to 70 cups of coffee daily to achieve the equivalent dose used in the study.

Two years later, the FDA’s concerns were reinforced by a study of 12,000 pregnant women that linked drinking four or more cups of coffee daily to premature birth and low birth weight. But while smoking turned out to be the chief culprit, the agency has yet to ease its warning.

2 Risk of miscarriage

Although numerous studies on caffeine and the risk of miscarriage have been published since the 1980s, its effect on the risk of miscarriage remains controversial. The results from the recent Kaiser Permanente Study provide newer, stronger evidence that high amounts of caffeine during pregnancy may increase the risk of miscarriage.

This population-based, prospective cohort study examinated the effect of caffeine intake during pregnancy on the risk of miscarriage, taking into account a number of potential confounders, especially the impact of nausea or vomiting during pregnancy.

Prior studies also had linked high caffeine consumption among pregnant women to an elevated risk of miscarriage. But those studies didn’t prove that drinking coffee can actually lead to a miscarriage. They showed only a statistical link. The new study, in part by tracking women from early in pregnancy through delivery or miscarriage, makes a more convincing case for a cause-and-effect relationship.

Researchers looked at 1,063 pregnant Kaiser Permanente members in San Francisco from October 1996 through October 1998, examined the caffeine effect among women who never changed their pattern of caffeine consumption during their pregnancy. They found:

  • Women who consumed 200 mg or more of caffeine per day (two or more cups of regular coffee or five 12-ounce cans of caffeinated soda) had twice the miscarriage risk as women who consumed no caffeine.
  • Women who consumed less than 200 mg of caffeine daily had more than 40 percent increased risk of miscarriage.
  • Women who were nonsmokers and who had no history of a miscarriage experienced higher risks for miscarriage associated with caffeine.

3 Birth weight and preterm birth

One of the most rigorous studies ever to examine the issue found no link between moderate caffeine consumption late in pregnancy and either preterm delivery or low birth weight. Danish interventional study (randomized, double-blind trial) by Bech and colleagues showed that babies born to mothers who drink moderate amounts of coffee do not weigh less than those whose mothers’ drink decaffeinated coffee in the second half of pregnancy.

The Danish researchers looked at 1,200 healthy pregnant women who reported drinking at least three cups of caffeinated coffee a day, and who were less than 20 weeks pregnant when they entered the study. The women were randomized to receive caffeinated or decaffeinated instant coffee. The average daily intake of caffeine for women who drank mostly decaffeinated coffee was 117 milligrams a day — roughly the amount of caffeine found in three 12-ounce soft drinks. Women in the caffeinated-coffee group ended up consuming about 317 milligrams of caffeine a day — the equivalent of four cups of instant caffeinated coffee, or two and a half cups of brewed coffee. Mean caffeine intake was 182 mg lower in the decaffeinated-coffee group than in the other group (the equivalent of approximately 3 cups of instant coffee a day).

There were no significant differences for mean birth weight or mean length of gestation between infants of women in both groups. However, the study did not address the safety of coffee during the early months of pregnancy or the impact of very large amounts of coffee .

4 Risk of stillbirth

During the previous research Bech group have come to conclusion, that more than nine cups of coffee a day can increase the risk of stillbirth.

Researchers in Denmark identified 18,478 pregnant women booking for delivery at Aarhus University Hospital during 1989-1996. The women completed two questionnaires, providing information such as medical history, smoking habits, alcohol and coffee consumption. The risk of stillbirth increased with the number of cups of coffee a day during pregnancy. Compared with women who did not drink any coffee, women who drank four to seven cups a day had an 80 per cent increased risk of stillbirth, and women who drank eight or more cups a day had a 300 per cent increased risk. These results seem to indicate a threshold effect around four to seven cups per day.

Interestingly, there was no association between coffee and death in the first year of life.

Women with a high intake of coffee are more likely to be smokers and to have a high intake of alcohol, the authors suggest. Adjusting for these factors reduced the risk slightly, but the link remained significant.

After decades of controversy and conflicting evidence, there’s still no real consensus on the safety of coffee during pregnancy. So what can we find out from modern research?

It is necessary to limit intake of coffee during pregnancy because there is no clear proof that it is safe during this period. At the same time, one or two cups a day probably won’t pose a problem for most women. But woman who has had recurrent pregnancy losses or who is having problems becoming pregnant might want to consider avoiding coffee.