Estrogens

By RRM Academy Reviewed by Dr. Naomi Whittaker, MD, Board-Certified OBGYN, MIGS, NFPMC, FCI Updated August 8, 2026

Estrogens are a class of steroid sex hormones essential for female reproductive development and function. The four principal endogenous forms are estradiol (E2), estrone (E1), estriol (E3), and estetrol (E4).¹ Granulosa cells of developing ovarian follicles produce estradiol, the dominant and most potent form in reproductive-aged women. Estetrol is produced only during pregnancy, synthesized by the fetal liver within the fetoplacental unit and reaching the maternal circulation through the placenta; it plays no meaningful role outside gestation.¹

Estrogens drive endometrial proliferation, promote fertile-quality cervical mucus production, stimulate the preovulatory LH surge through positive hypothalamic-pituitary feedback, and support follicle maturation. During pregnancy, estriol supports uteroplacental blood flow and serves clinically as a marker of fetoplacental function.

In Restorative Reproductive Medicine, cycle-timed estradiol measurements are central to the comprehensive hormonal panel. Draws in the early follicular phase and again after Peak allow RRM clinicians to assess follicular adequacy, luteal function, and estrogen support for the endometrium, rather than relying on a single snapshot.

This content is for educational purposes only and does not constitute medical advice. Consult an RRM clinician or healthcare provider for guidance specific to your situation.