human chorionic gonadotrophin (hcg) is a pregnancy hormone present in your blood from the time of conception and is produced by the cells that form the placenta. this is the hormone detected in a pregnancy test; but it usually takes three to four weeks from the first day of your last period for the levels of hcg to be high enough to be detected by pregnancy tests. the development stages of pregnancy are called trimesters or three-month periods because of the distinct changes that occur in each stage.
what are pregnancy hormones?