EFFECT OF CAFFEINE DURING PREGNANCY...

There's general agreement that pregnant women and those trying
to conceive should avoid consuming large quantities of caffeine.
But after decades of controversy and conflicting evidence, there's
still no consensus on how much caffeine is safe during pregnancy.
On the side of caution, the March of Dimes advises women
to limit their caffeine intake to less than 200 milligrams per day,
which is about one 12-ounce cup of coffee. (See the chart below to
get a sense of the amount of caffeine in common beverages and
foods.)

A highly publicized 2008 study found that women who consumed
200 mg or more of caffeine a day had double the risk of
miscarriage of those who took in no caffeine. However, not all
studies show a link between caffeine consumption and a higher
risk of miscarriage.
A study in Denmark found that the risk of stillbirth more than
doubled in women who drank eight cups of coffee or more each
day compared with women who didn't drink coffee.
Other research has shown that newborns whose mother consumed
more than 500 mg of caffeine a day had faster heart rates and
breathing rates and spent more time awake in the first few days
after birth.
Some studies show an association between high caffeine
consumption and a slight reduction in the baby's birth weight, but
other research has shown no link. There does not appear to be an
association between moderate caffeine consumption and preterm
birth . And caffeine consumption does not appear to increase the
risk of gestational hypertension or preeclampsia .
One thing's for sure: You'll feel better if you don't consume a lot of
caffeine. It's a stimulant, so it raises your heart rate. Plus, it can
make you feel jittery and cause insomnia . Caffeine can also
contribute to heartburn by stimulating the secretion of stomach
acid.
These effects may be more pronounced as your pregnancy
progresses. That's because your body's ability to break down
caffeine slows, so you end up with a higher level of it in your
bloodstream. During the second trimester, it takes almost twice as
long to clear caffeine from your body as when you're not pregnant.
During the third trimester, it takes nearly three times as long.
This can affect the amount of caffeine that crosses the placenta
and reaches your baby, who can't process it efficiently. (This is
true for newborn babies as well, which is why it's also a good idea
to limit caffeine if you're breastfeeding, especially for the first few
months.)
Finally, there's one more reason to cut back on coffee and tea,
whether it's caffeinated or not. These beverages contain
compounds called phenols that make it harder for your body to
absorb iron. This is particularly important because many pregnant
women are already low on iron. If you have coffee or tea, drink it
between meals so it'll have less of an effect on your iron
absorption.