Summary: Several studies have shown that consumption of caffeine (equivalent to 1 cup of coffee) is associated with a twofold increase in miscarriage.
Possible good news: The studies may have been skewed by women with healthy pregnancies reducing their caffeine intake due to morning sickness.
New Scientist reports this in the 26 January 2008 edition (p19 bottom right).
One study interviewed 1063 women through to the 20 week mark (of pregnancy) or until miscarriage.
200mg of caffeine (just over a cup of coffee) was enough to produce the devastating twofold miscarriage finding. The caffeine could be consumed in cola, tea, hot chocolate as well as coffee.
The reason, according to De-Kun Li (at the California-based Health insurer Kaiser Permanente) who conducted the interviews, could be due to caffeine constricting the blood vessels that flow to the placenta.
Here's the conclusion from another study (choose the Science Direct link) conducted by American Journal of Obstetrics and Gynecology:
"Our results demonstrated that high doses of caffeine intake during pregnancy increase the risk of miscarriage, independent of pregnancy-related symptoms."
Sadly, we discover more and more just how fragile life is. The balance is so precious – no wonder birth is often referred to as 'the miracle of life'. And how distressing for mothers-to-be. So many things to absorb, understand and avoid. I can only imagine how anxiety-inducing this and other studies must be to women entering what should otherwise be a wonderful, joyous time.