It's called Dysgeusia. Very common in pregnancy.
What it is: Dysgeusia is the medical term for a change in your sense of taste; most often, you'll get a sour or metallic taste (yuck!) that persists even when you're not eating.
What causes the metallic taste: Hormones, and in particular estrogen, seem to play a role in controlling and moderating our sense of taste. And when you're pregnant, estrogen levels — and hence your sense of taste — may fluctuate widely. Plus, your sense of taste and your sense of smell are intimately connected, so pregnancy-related changes in your sense of smell may also lead to dysgeusia.
What you need to know about it: For something we don't hear much about, dysgeusia is surprisingly common in pregnancy. Like morning sickness, it should get better (or, if you're lucky, disappear altogether) in your second trimester when those hormones begin to settle down a bit.
What to do about it: Try banishing that metallic taste with acids. Focus on sour flavors such as citrus juices, lemonade, and — assuming your tummy can handle them — foods marinated in vinegar (pickles anyone? After all, you are pregnant). All these foods not only have the power to break through the metallic taste in your mouth, they also increase saliva production, which will help wash it away. You might also talk to your practitioner about changing your prenatal vitamin; some seem to lead to metal mouth more than others.
Another trick: Try brushing your tongue each time you brush your teeth, or rinse your mouth with a mild salt solution (a teaspoon of salt in eight ounces of water) or a baking soda solution (1/4 teaspoon baking soda in eight ounces of water) a few times a day to neutralize pH levels in your mouth and keep away that flinty flavor.