If you’ve received a positive on a pregnancy test, congratulations! False positives are incredibly rare, though many people still mistake a negative with a positive on an analog home pregnancy test. Always make sure you read the instructions on your pregnancy test carefully!

Pregnancy tests, whether taken at home or at the doctor’s office, test for a hormone called hCG in the blood or urine. HCG is a very good indicator of pregnancy; the chemical is released by placental tissues as part of placental implantation, and remains critical throughout pregnancy.

That means that, for the most part, if you get a positive on a pregnancy test, conception has already occurred. There are a few rare cases where a test may detect chemicals other than hCG. There are also very rare situations where your pituitary or cancer cells in your body may be producing hCG. These are virtually never the cause of a “false positive.” Rather, what many women confuse with a false positive is actually a chemical pregnancy — a type of miscarriage.

HCG levels begin to rise incredibly early on in a pregnancy and some tests may detect hCG as soon as a week after conception. This is generally referred to as the “chemical” or “biochemical” phase of pregnancy — at this point, there hasn’t been enough development for the pregnancy to be detected via ultrasound or really by any method other than the presence of hCG.

The problem is, at this stage, miscarriage is common. It’s estimated that as many as 60% of all pregnancies miscarry before they become visible via ultrasound. Before the prevalence of home pregnancy tests, a woman typically wouldn’t even know when she had experienced one of these early miscarriages (usually referred to as a chemical pregnancy). Now, many women are finding themselves heartbroken over a loss they would never have known about, and some doctors are wondering if these early home pregnancy tests are a good idea.

They are. But they don’t necessarily mean what we want them to mean. These miscarriages often occur for very good reasons — reasons like chromosomal disorders or ectopic pregnancies, where the pregnancy simply isn’t viable. It can still be hard for some women to experience this loss, which is why some doctors suggest waiting longer before testing for pregnancy.

However, many women don’t begin to improve their health habits until after they know that they are pregnant. That little plus sign can be a great motivator to kick the caffeine habit, stop drinking that glass of wine with dinner, and to start taking your prenatal multivitamin. And the sooner you do those things, the healthier your baby will be!