A cup of coffee increases the risk of premature babies, according to a study

Moms should wake up and smell the coffee.

Women who drink caffeine during pregnancy are more likely to have preterm and low birth weight babies, and health researchers recommend that exhausted future mothers consider new ways to wake up.

A new study, published in the American Journal of Clinical Nutrition, examined 941 births in Ireland, where the drink of choice containing caffeine happens to be tea. About 40% of mothers reported drinking coffee, which can contain twice as much caffeine.

The World Health Organization recommends that pregnant women consume less than 300 mg of the regular stimulant daily, while the American College of Obstetricians and Gynecologists (ACOG) suggests consuming 200 mg – about one cup.

But even women who have adhered to these established guidelines are exposing their unborn children to greater risk, according to the researchers.

The results were striking: each additional 100 milligrams of caffeine consumed daily during the first trimester resulted in a birth weight loss of approximately 2.5 ounces. Women in the upper end of the caffeine spectrum had babies weighing about 6 ounces less than those who drank the least amount of coffee or tea. The size and head circumference were also affected, as was the gestational age.

"A high intake of caffeine can result in limited blood flow in the placenta, which can then affect fetal growth," Reuters told Reuters, the study's lead author, Ling-Wei Chen. "Caffeine can also easily cross the placenta and, since caffeine clearance slows as pregnancy progresses, caffeine buildup can occur in fetal tissue."

Chen and his colleagues worry that people do not know that some teas contain a considerable amount of caffeine and that some black teas, for example, can hold almost as much as a cup of coffee.

Although the observational study can not definitively prove that caffeine slows its growth in utero, several researchers confirmed the conclusion of this study.

ACOG reviews all new research and re-evaluates its guidelines every 18 to 24 months, telling Reuters: "So far, the current ACOG guidelines still hold."