Caffeine is a stimulant that causes increased heart rate and blood pressure. It also acts as a diuretic, causing increased urination, which can lead to dehydration. Coffee and other caffeinated foods also cause heartburn for some women. It is important to carefully monitor your caffeine intake throughout pregnancy, particularly in the third trimester when the fetus is in the final stages of preparing for birth. At this time she has a fully developed skeleton and open eyes that can detect changes in light. Her lungs are continuing to develop and she is gaining weight at a rate of half a pound per week to prepare for birth.
Effects on Fetus
Caffeine consumed by the mother is passed to the fetus through the placenta, along with oxygen and nutrients, according to the American Pregnancy Association. Moderate caffeine consumption may cause increased alertness in utero or at birth and can change a fetus's sleep patterns. However, large amounts of caffeine have been connected to low birth weight, increased risk of miscarriage and, rarely, heart defects. This is particularly important during the third trimester, when the baby is gaining a significant amount of weight. Caffeine consumption at this time can negatively affect birth weight.
The March of Dimes recommends that pregnant women have no more than 200mg of caffeine per day. Although different types of coffee vary in their caffeine content, one 12-oz. cup of coffee is close to this limit. Other experts recommend limiting caffeine to between 150mg and 300mg per day. A 2003 study at the Norwegian University of Science and Technology found that a high caffeine intake in the third trimester of pregnancy, defined as an average of 280mg of caffeine, doubled the risk of having a baby with low birth weight.
The highest caffeine levels in food are found in brewed coffee, which can range from 137mg in 8 oz. to 200mg. Instant coffee is a better choice with 75mg per 8-oz. cup. Teas have between 40 and 45mg of caffeine per cup, and cola has 37mg. Other sources of caffeine in the diet include chocolate and headache medications with added caffeine. It is important to consider serving size because most restaurant coffees and sodas are larger than 8 oz.
Instead of regular coffee, choose tea or decaffeinated coffee. Check with your doctor before drinking any herbal teas. They are not made from the same plant as green and black tea, and although they have lower levels of caffeine, they may have ingredients that are not safe during pregnancy. The American Pregnancy Association lists peppermint leaf, red raspberry leaf and lemon balm teas as likely safe, but recommends caution when using other herbal teas.