Estrogens

Estrogens are a group of steroid sex hormones. Women need them for reproductive development and function. The body makes four main forms: estradiol (E2), estrone (E1), estriol (E3), and estetrol (E4).¹

Granulosa cells, the cells that line growing egg follicles, make estradiol. Estradiol is the main and most potent form in women of reproductive age. The body makes estetrol only during pregnancy. The fetal liver produces it, and it reaches the mother's blood through the placenta. It plays no meaningful role outside pregnancy.¹

Estrogens build up the endometrium, the lining of the uterus. They help the cervix produce fertile-quality cervical mucus. They signal the brain and pituitary gland to trigger the LH surge before ovulation (positive feedback). They also help follicles mature.

In pregnancy, estriol supports blood flow to the uterus and placenta. Clinicians also use it as a marker of how well the fetus and placenta are functioning.

Many restorative clinicians make estradiol tests timed to the charted cycle a central part of a full hormone panel. They test early in the cycle (the early follicular phase) and again after Peak, rather than relying on one snapshot. This timing shows how well follicles grow and how well luteal function holds up. It also shows how well estrogen supports the endometrium.