Caffeine travels within the bloodstream and crosses into the placenta. Since it is a stimulant, it can cause your baby’s heart rate and metabolism to increase. Too much caffeine can also cause slowed fetal growth and increase risk of miscarriage. In most cases, a little caffeine is safe during pregnancy.
According to the Mayo Clinic, there is some evidence that large amounts of caffeine can interfere with estrogen production and metabolism, making it harder to get pregnant. If you have lumpy breasts, are pregnant, or are trying to get pregnant, ask your doctor about safe levels of caffeine.
Source: Health Line