A chemical pregnancy is a very early pregnancy loss that happens just after the embryo implants. An ultrasound wouldn’t detect a fetus, but your body produces the hCG hormone so the result would be positive. Unless you took a pregnancy test, you wouldn’t know you had been pregnant, as a chemical pregnancy will show very few symptoms, and you wouldn’t experience pregnancy-related signs like morning sickness. Many experts think that chemical pregnancies occur for similar reasons as many other miscarriages - due to chromosomal problems with the developing baby.