COFFEE EFFECT ON PREGNANCY...

What we found is that for women whose caffeine intake
was more than 200 mg every day, the risk of miscarriage was
double compared with women who did not have any caffeine
during pregnancy. For those who consumed more than 200
mg a day, their miscarriage rate was about 25%. Below 200
mg, we also saw a slight increase in risk, [but] we were not
able to make a more definitive assessment. Generally
speaking, though, for environmental exposure

in the context of miscarriage, there is rarely a threshold
effect. Usually, the higher the dose, the bigger the effect.
There are two mechanisms that have been hypothesized up to
this point, linking caffeine to miscarriage. First, we know that
caffeine can directly, easily cross the placental barrier. While
adults can usually metabolize caffeine, a fetus usually can't,
particularly in the early stages of development. So caffeine
has a direct effect on cells, membranes and tissues. Those
kinds of things for adults are OK. That's why we actually
drink caffeine — because it interacts with our cell receptors.
But for a fetus, particularly at the early stages of
development, it may interfere with development.
Second, it's been known for a long time that high doses of
caffeine can have a vaso-constrictive effect, which
means it can make blood vessels contract. If the effect is
severe in the mother, hypothetically it can reduce blood flow
to the placenta and to the fetus. It's totally possible that there could be other outcomes, like low birth weight,delivery, even birth defects,neurological development.
The message here is probably the less, the better. I would
think if you wanted to be safe, you should probably cut down
or even stop caffeine-drinking throughout pregnancy.