HCG: How Your Pee-On-A-Stick Pregnancy Test Knows You Are Preggers - Allbodies

HCG: How Your Pee-On-A-Stick Pregnancy Test Knows You Are Preggers

HCG: How Your Pee-On-A-Stick Pregnancy Test Knows You Are Preggers

HCG: How Your Pee-On-A-Stick Pregnancy Test Knows You Are Preggers

Ever wonder how a plastic pee-stick can tell whether you’re pregnant?

The answer is HCG (Human Chorionic Gonadotropin). HCG is a hormone produced by the placenta after embryo implantation. This is why elevated HCG levels indicate pregnancy – because the placenta only exists when you’re pregnant. So, you grow a fetus and an organ, and that organ produces its own hormones- like HCG!


HCG is v. important because it promotes estrogen and progesterone production which helps to sustain the pregnancy.

Morning sickness (nausea and vomiting during the first trimester) has also been linked to high levels of HCG, and is the result of these increasing hormone levels in your body. While it’s generally an unpleasant experience – the medical community seems to agree it may be a good sign! Some theories suggest that morning sickness may be evolutionary adaptation, by causing the body to expel certain foods (i.e. meat and strong-tasting vegetables) that historically contained (and may still contain) parasites and other harmful toxins that could be damaging to the fetus.

Didn't get the sex-ed you wanted?

Same. So we made you classes on sex + pleasure, trauma, body literacy, racism + sexism, mental health + more!


Levels of HCG vary depending on how far along you are into your pregnancy. Levels will begin rising around 7-12 days after sex, and then doubling every 48-72 hours in the first weeks of pregnancy, so someone that takes a pregnancy test too early, may not have detectable levels of HCG just yet. HCG can be detected in both urine, and blood, though higher levels of HCG are required for urine testing, leading to that agonizing waiting period for take-home tests.

Though low or declining HCG levels can indicate miscarriage or ectopic pregnancy (when the fertilized egg implants in the fallopian tube or somewhere else in the abdomen – never making it all the way to your uterus), they aren’t always cause for concern and should not be used alone in making a diagnosis. Your doctor may want to conduct an intervaginal ultrasound to confirm any indication of pregnancy and to calculate an accurate gestational age.


There are some cancers that produce HCG so it is possible to have elevated HCG levels when you aren’t pregnant. This, along with other underlying conditions (such as PCOS), and some medications, are the most common causes of a “false-positive” on a take home pregnancy test.


In addition to being a tool for identifying pregnancy, HCG is sometimes used to treat infertility via intrauterine injection. HCG mimics the effects of LH (Luteinizing Hormone), triggering egg maturation and the dropping of the egg (ovulation). It is often used in conjunction with a IUI (Intrauterine Insemination), IVF (In Vitro Fertilization), or ICSI (Intracytoplasmic Sperm Injection), and on those with PCOS (Polycystic Ovary Syndrome) for this reason.

Similarly, HCG can also be used in those assigned male at birth via injection to stimulate the pituitary gland and encourage testosterone production and an increased sperm-count – it’s also sometimes used on adolescents to correct undescended testes. Talk about multi-talented!


HCG is a fetus-sustaining hormone intrinsic to a healthy pregnancy, AND can be used to support other phases of fertility, like inducing ovulation or spermatogenesis. It may be a superpower of a hormone, but it’s not above a store-bought pregnancy test.

Written by: Morgan De Santo, reproductive health specialist