Can You Measure hCG Levels in Your Urine?

Yes—and no. Measuring hCG in urine is how home pregnancy tests (HPTs) work. When you pee on a stick, the spongy material that soaks up your urine is treated to detect the presence of hCG, which stands for human chorionic gonadotropin—the hormone produced by the placenta, the organ that forms during pregnancy to provide nourishment to a developing fetus. This hormone usually is present in urine by 10 days after a newly pregnant woman misses her first period, which typically is when the fertilized egg attaches to the walls of the uterus.

Urine tests can't confirm pregnancy as early as blood tests performed by a doctor can, of course. But since they first became available in 1977, HPTs have become more and more sensitive and now can confirm a pregnancy within a few minutes. (They've also become much easier to use: The first home tests involved purified water, test tubes, and other items, plus a lot of patience.) What an HPT can't tell you, however, is how much hCG is in your urine.

This is relevant because during the first several weeks of a pregnancy that's progressing normally, hCG levels rise rapidly. When hCG levels don't increase as expected, it can be an indication that the pregnancy may not be viable. Often the hCG levels of a woman who got pregnant while undergoing infertility treatment will be monitored closely by her doctor to make sure everything is developing as it should.

How Reliable are HPTs?

Most home pregnancy tests claim to be 99% accurate, but research shows that not all brands are equally sensitive. While some tests can give reliable results as soon as a woman misses her period, there's a chance of getting a false-negative that early.

Since the sooner after learning she's expecting a woman should begin making lifestyle changes to support the healthy development of her baby, if she gets a false-negative on an HPT and assumes she's not pregnant, she may continue to do things that could affect her pregnancy, such as drinking or smoking. For this reason, the U.S. Food and Drug Administration advises waiting one to two weeks after you've missed your period to use an HPT.

What about a false-positive result? This is very rare; if you aren't pregnant your body simply will not product hCG. However, if you became pregnant and then lost the pregnancy without knowing it, there might be enough residual hormone in your urine for an HPT to detect. Other potential causes of a false-positive home pregnancy test include gestational trophoblastic diseases, menopause, or problems with the ovaries.

Getting Accurate Results

Again, you should wait a week or two after you miss your period to do a home pregnancy test. If you've been trying to get pregnant and you want to do one sooner, of course that's fine; just don't be disappointed or assume you didn't conceive if you get a negative results. Wait and do the test again if you don't get your period after a week or two.

It's also best to do the test first thing in the morning. This is when your urine is most concentrated and will contain the highest and most easily detectable amounts of hCG.

Most importantly, read and follow the directions that came with your test. Some provide detailed instructions for how to hold the stick and for how long to leave it in your urine stream, for instance. And always follow up with your doctor as soon as you get a positive result on a home pregnancy test.