NEW YORK (Reuters Health) - A new analysis adds to evidence that pregnant women can have a morning cup of coffee without fearing they will raise their risk of preterm delivery.
Combining the results of 22 previous studies, researchers found no evidence that pregnant women who downed the most caffeine -- roughly equivalent to three to four cups of coffee per day -- had a higher risk of preterm birth than women who avoided caffeine throughout pregnancy.
Nor did they find any link between the amount of coffee the women drank and their odds of an early delivery.
Approximately 12 percent of births in the U.S. and 7 percent of births in Europe are pre-term -- occurring before the 37th week of gestation - according to the authors, whose report appears in the American Journal of Clinical Nutrition.
Earlier this year, the American College of Obstetricians and Gynecologists (ACOG) issued a statement saying that pregnant women who consume up to 200 milligrams (mg) of caffeine per day -- about the amount in two 8-ounce cups of coffee -- are unlikely to raise their odds of miscarriage or preterm delivery.
Whether higher caffeine intake might boost those odds remains unclear, according to ACOG.
However, the group also cautions that there are other reasons pregnant women may opt to avoid caffeine.
Some research, for example, has found an association between maternal caffeine intake -- even as little as 100 mg per day -- and low birth weight. Although such studies do not prove that caffeine is the cause, pregnant women may want to err on the side of caution and limit their intake.
In addition, ACOG notes, excess caffeine could make pregnancy tougher by interfering with a woman's sleep or contributing to nausea and light-headedness. It can also boost urination and lead to dehydration.
The latest findings do not mean that caffeine is entirely "safe" for pregnant women. But they do support the conclusion that, at least in moderate amounts, it does not contribute to preterm births, according to the researchers, led by Ekaterina Maslova of the Harvard School of Public Health.
Their analysis included 22 studies from the U.S., Canada, Europe and Brazil looking at the relationship between pregnant women's reported intake of coffee, tea and other caffeine sources and their odds of preterm birth.
The two largest studies each included more than 40,000 women.
Individually, the studies differed considerably in their conclusions -- with eight showing either an increased or a decreased risk of preterm delivery among women who consumed higher levels of caffeine during pregnancy. The rest showed no clear connection between caffeine and preterm birth, according to Maslova's team.
Similarly, when the researchers combined the data from all the studies, they found that women who reported having 300 mg of caffeine or more each day, during any trimester, had no higher risk of preterm birth than women who consumed little to no caffeine.
Still, the results leave open some questions, according to Maslova and her colleagues.
They point out that most of the research they analyzed did not measure caffeine intake beyond 400 mg per day, so it is not clear whether higher intakes might affect preterm delivery risk.
In addition, most of the studies included mainly white women. Maslova and her colleagues say there is still a need for studies examining more diverse groups of women to see whether there are any ethnic differences in the relationship between caffeine and preterm birth.
Genetic differences in how individuals metabolize caffeine could also, in theory, influence any effects of caffeine on pregnancy, the researchers note.
Further assessing the effects of higher total caffeine intakes, above 400 mg a day, will be "especially important," they conclude, in light of new caffeine sources beyond coffee and tea -- such as enhanced bottled waters, energy drinks and herbal supplements, whose caffeine content is often not recognized.
SOURCE: link.reuters.com/puf85p American Journal of Clinical Nutrition, online September 15, 2010.