Which hormone's levels rise significantly during pregnancy?

Human chorionic gonadotropin (hCG) is the hormone whose levels rise significantly during pregnancy. It is produced shortly after the fertilized egg attaches to the uterine lining and is critical for maintaining the early stages of pregnancy. hCG's primary role is to signal the corpus luteum to continue producing progesterone, which is essential to sustain the uterine lining and prevent menstruation during the initial weeks of pregnancy.

The presence of hCG is what pregnancy tests detect, as it can be measured in urine or blood, confirming pregnancy. Levels of hCG typically peak between the 8th and 11th weeks of gestation before declining to lower levels later in the pregnancy. This distinctive pattern of secretion makes hCG a key hormone for both confirming pregnancy and monitoring its progression.

In contrast, while estrogen and progesterone also increase during pregnancy, they do so as a result of signals from hCG and other factors as the pregnancy progresses. Luteinizing hormone (LH) actually decreases during pregnancy since its primary role in triggering ovulation and regulating the menstrual cycle is supplanted by the hormonal changes initiated by hCG.