Pregnancy, which is characteristically associated with changes in hormone levels in the body is a process tightly regulated by:

Pregnancy, which is characteristically associated with changes in hormone levels in the body is a process tightly regulated by the hormon Human Chorionic Gonadotropin

Explanation:

The so-called pregnancy hormone is the Human Chorionic Gonadotropin (HCG). It only occurs during the gestation period and is responsible for regulating the entire process. Segregated by the placenta, it can be found in urine and blood.

The presence of the hormone in the urine allows to confirm the pregnancy with the test. As in pregnancy, the placenta begins to form, the cells that make it up begin to stimulate the production of HCG, which causes the hormone levels to increase very rapidly in the first trimester of pregnancy

The endocrine and nervous system.

Explanation:

Fertilization is the process of the fusion of the male gamete known as sperm with the female gamete known as ova and leads to the formation of zygote. The pregnancy period in humans is for nine months.

Different hormonal changes are noticed in the woman in case of pregnancy. Progesterone maintains the pregnancy and human chorionic gonadotropin is known as pregnancy hormone. The endocrine and the nervous system controls the pregnancy period.

Thus, the answer is endocrine and nervous system.