A chemically reactive strip that a woman pees on to see if she is pregnant. Here’s how home pregnancy tests work: when a fertilized egg implants itself into the wall of the uterus, the placenta starts to grow and it releases a hormone known as human chorionic gonadotropin or hCG which is called the pregnancy hormone. It’s what the home pregnancy tests are looking for. However, a woman needs to wait for 10 or 11 days after conception for the hCG levels to start being detectable in her urine and in her blood. And it can take a few days longer than that for the hCG to be high enough to reliably register on home pregnancy tests. This is why Planned Parenthood and other organizations recommend that a woman should wait until the first day when she expects her next menstrual cycle to begin before taking a home pregnancy test. It is also very important to read the instructions on the test carefully and follow them exactly. Instructions can vary from brand to brand and from year to year.