Extra Caffeine May Mean Smaller Baby

Caffeine intake during pregnancy linked to lower birth weights in babies

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) When the sluggishness from being pregnant hits you, it's tempting to brew a cup of coffee. And then another. And another. But does too much caffeine during pregnancy may affect your baby?

A recent study looked at the relationship between women's caffeine intake and their pregnancies.

Caffeine from any source was linked to slightly lower birth weights - about an ounce less for every 100 mg of caffeine per day that women consumed.

The researchers also found that women had longer pregnancies if they drank more than 100 mg of caffeine per day specifically from coffee.

This particular link suggested that an ingredient in coffee besides caffeine may be responsible for the longer pregnancies. However, researchers weren't sure what the ingredient was.

"Limit caffeine intake while pregnant."

The study, led by Verena Sengpiel, MD, PhD, of the Department of Obstetrics and Gynecology at Sahlgrenska University Hospital in Sweden, looked for possible links between caffeine intake and pregnancy outcomes.

The researchers studied 59,123 Norwegian women who were pregnant with a single child.

The women reported how much caffeine they consumed from different sources when they were 17 weeks, 22 weeks and 30 weeks pregnant.

The researchers then looked at how many of the women gave birth early (between the 22nd and 36th week of pregnancy) and how many of their babies were born small for the week of pregnancy in which they were born. The researchers also gathered data on the babies' birth weights.

The women reported an average intake of 126 mg of caffeine a day before they became pregnant. Both before and during pregnancy, most of the women got their caffeine from drinking coffee.

When the women were 17 weeks pregnant, half the women reported consuming more than 44 mg a day and half reported consuming less than 44 mg a day. When the women were 30 weeks pregnant, the midpoint of caffeine intake was 62 mg a day.

The researchers compared the women's caffeine intake to their pregnancy outcomes and found that caffeine consumed specifically from coffee was related to a longer gestation period, or length of pregnancy.

For every 100 mg a day of caffeine the women drank, their pregnancies were typically about eight hours longer. For example, a woman who drank 300 mg of caffeine from coffee each day of her pregnancy would have a pregnancy lasting one day longer than a woman who did not consume any caffeine from coffee while pregnant.

However, caffeine from other sources, such as tea or chocolate, did not appear linked to the length of the women's pregnancies. Therefore the researchers said it did not appear to be the caffeine in coffee that was causing the longer pregnancies. Rather, the longer pregnancies may be linked to something else in coffee, or may be related to another characteristic of women who also drink more coffee than others.

Caffeine from any source did not appear linked with preterm (early) birth. However, caffeine intake from various sources did appear linked to a baby's birth weight.

For a baby of average weight (about 7.9 pounds), each additional 100 mg of caffeine per day during pregnancy meant the baby weighed about 0.7 to 1 ounce less.

An increased risk for having an underweight baby ("small for gestational age") did not occur until women consumed 200 to 300 mg of caffeine per day. At this amount of daily caffeine, women were 27 to 62 percent more likely to have a small-for-gestational-age baby than women who had only 50 mg of caffeine or less each day.

The World Health Organization currently recommends that pregnant women limit their caffeine intake to 300 mg per day. Some countries, including the United States and Scandinavian countries, recommend a lower maximum of 200 mg per day.

However, this study showed that this upper limit may still increase a woman's risk of delivering a baby that is small for the pregnancy week when the baby is born.

According to the Mayo Clinic, an eight-ounce cup of standard brewed coffee has anywhere from 95 to 200 mg of caffeine, depending on how it was brewed. Green tea and black tea have about 14 to 61 mg of caffeine per eight ounces.

A standard soft drink (12 ounces) has about 30 to 35 mg of caffeine, and an eight-ounce energy drink has about 80 mg of caffeine. One cup of semisweet chocolate chips has about 100 mg of caffeine.

The study was published February 18 in the journal BMC Medicine. The research was funded by the Norwegian Ministry of Health, the Norwegian Ministry of Education and Research, the US National Institutes of Health, the Norwegian Research Council, the European Commission and the Swedish Medical Society. The authors declared no conflicts of interest.

Reviewed by: 
Review Date: 
February 18, 2013
Last Updated:
August 16, 2013