During the proliferative phase, uterine glands appear long due to estrogen secretion by the ovaries.

The functional layer of the uterus containing the glands becomes necrotic, and eventually sloughs off during the menstrual phase of the cycle.

They are of small size in the unimpregnated uterus, but shortly after impregnation become enlarged and elongated, presenting a contorted or waved appearance.

Hormones produced in early pregnancy stimulate the uterine glands to secrete a number of substances to give nutrition and protection to the embryo and fetus, and the fetal membranes.

[1] Some secretory components from the uterine glands are taken up by the secondary yolk sac lining the exocoelomic cavity during pregnancy, and may thereby assist in providing fetal nutrition.