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