Heat

Heat is good.

Heat means your body is making stuff. It's whirring.

If you're trying to conceive, your basal body thermometer is your first interaction of the day. It's a little fussy: you need to take your temperature before you get up, drink water, etc., and if you wake up early or late, the temperature is unreliable.

If you're a woman who ovulates, your body has two basic temperatures: in the first half of your cycle, before you ovulate, it's a little lower; say between 97.5 and 97.9. After you ovulate, the follicle that released an egg turns into a corpus luteum and releases progesterone. That raises your temperature, say to between 98.1 and 98.5. (You know how in the movies, the wife walks into the kitchen with a thermometer in her hand and says to her hubby, "I'm ovulating"? Total crap. Once your temperature has risen, it's over.) If you get pregnant and all is well, progesterone production will continue and your temperature will remain high. Some books say you're almost definitely pregnant if your temperature remains high for 18 days.

If you don't get pregnant, your progesterone will fall around the time your period arrives. Which means that if you're waiting to find out if you're pregnant, you can get a preview by watching your temperature. A single dip isn't bad -- sometimes this is caused by a fertilized egg implanting into the uterus -- but multiple dips are an unhappy trend. My period isn't due for two days (though I took Clomid this cycle, which can make things screwy), but my temperature was down this morning and yesterday. Toss that in with some cramps and a bit of low back pain, and you've nearly got yourself a negative pregnancy test with no signs of blood and without peeing on a stick.