| When you feel the first symptoms of pregnancy, | | | | fertilized egg has attached to the uterine wall. This |
| you naturally head to the drug store to find a | | | | usually occurs within 14 days of fertilization, so a |
| good pregnancy test. Have you ever wondered | | | | blood test is almost always accurate if it's done |
| how they work? | | | | after your next period was supposed to start. |
| Over-the-counter pregnancy tests look for the | | | | Some over-the-counter tests need higher levels |
| presence of the "pregnancy hormone" in your | | | | of the hormone to be accurate, and so they say |
| urine. The test you receive later in your doctor's | | | | you're not pregnant, even though you are. You |
| office looks for the same hormone in your blood. | | | | can take another test a few days later to be |
| The hormone is called human chorionic | | | | sure. |
| gonadotropin, or hCG for short. This hormone | | | | Can you get a false positive result? |
| begins to build up just a few days after the | | | | Yes, your test may say you're pregnant even |
| fertilized egg is implanted in your uterine wall. The | | | | though you're not. The most common cause is |
| hCG will cause your placenta to produce | | | | waiting too long to read the results of the test - |
| progesterone after the implantation of the | | | | the urine will evaporate from the test strip, and |
| embryo, which is necessary to prevent the | | | | the color will change to show a positive result. If |
| embryo's rejection. | | | | you get a positive result but you waited longer |
| Because it takes time for the hormone to build up | | | | than suggested by the test's instructions, you'll |
| to detectable levels, most over-the-counter | | | | want to take the test over. |
| pregnancy tests work best when taken a few | | | | If you're taking fertility hormones, a home |
| days or a week after your missed period. Some | | | | pregnancy test may show a false positive result. |
| brands claim to be accurate sooner, but all | | | | Ask your doctor if your injections include the |
| women ovulate at different times of their cycles, | | | | hormone hCG. If so, the hormone will show up on |
| so this may or may not be true for you. | | | | the test, and the reading will be inaccurate. |
| The most accurate test is done in your doctor's | | | | In very rare instances, a false positive reading is |
| office. A blood test can detect much lower levels | | | | caused by certain unusual forms of cancer. |
| of the pregnancy hormone than urine tests. If | | | | What about the rabbit? |
| you get a negative reading from your drug store | | | | In your grandmother's day, there were no |
| pregnancy test, but you still "feel" pregnant, you'll | | | | over-the-counter pregnancy tests. The doctor |
| want to make an appointment with your doctor. | | | | would take a urine sample, and inject the urine |
| Planned Parenthood offices also offer pregnancy | | | | into a female rabbit. If the rabbit was injected |
| tests and exams. | | | | with humane urine that contained the pregnancy |
| About 25 days after an egg is fertilized the fetus | | | | hormone, the rabbit's ovaries would change. It |
| can be seen by transvaginal sonography. | | | | usually took several days for the changes to take |
| What causes false negative test results? | | | | place, and the rabbit had to die before the lab |
| A false positive result may occur if you take your | | | | technicians could look at her ovaries. |
| test too early. The pregnancy hormone hCG does | | | | Fortunately, rabbits are no longer necessary for |
| not begin to build up in your system until after the | | | | pregnancy tests. |