Estrogen
→ Estrogen cannot be synthesized by placenta alone as it cannot utilize C21 steroid due to lack of enzyme 17 alpha hydroxylase.
→ Hence conversion of C21 to C19 is not possible (Diczfalusy’s concept).
→ Fetal adrenal gland produces DHEA-S which is utilized by placental enzymes to synthesize estradiol & estriol.
→ M/C estrogen during pregnancy-estradiol (E2)
→ M/C estrogen during pregnancy-estradiol (E2)
VERY IMPORTANT POINTS:
- C21 (17-OH-Progesterone) → C19 (Androstenedione). This reaction is needed for estrogen synthesis.
- DHEA-S- Dehydroepiandrosterone sulfate
- Hormone which was earlier used as a marker of fetal well- being-estriol (E3)
- Main product of fetal adrenal gland-DHEA-S.
- Hence the initiation of labor depends on sufficient availability of estrogen, which in turn depends on fetal DHEAS – which depends on fetal ACTH.
- So, if question says: Labor is initiated by: look for fetal ACTH/maternal estrogen in answer.
- This is the reason why in anencephaly where the adrenal glands are hypoplastic or absent, the complication is Post Dated Pregnancy.