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Estrogen and Progesterone Effects during Pregnancy

Learn more about how both estrogen and progesterone cause changes throughout pregnancy

mLpenguin

• 1 min read
Estrogen and Progesterone Effects during Pregnancy
Photo by HI! ESTUDIO / Unsplash

Reproductive System Effects

Progesterone

  • Maintains decidualized endometrium for implantation.
    • Protects
  • Suppresses myometrial contractions (prevents preterm labor).
  • Promotes cervical mucus plug formation.
  • Inhibits FSH/LH via negative feedback.
Low progesterone → miscarriage or luteal phase defect. Progesterone supplementation may be used in threatened abortion or IVF cycles.

Estrogen

  • Stimulates myometrial growth and uterine blood flow.
    • Evolves
  • Enhances oxytocin receptor expression late in pregnancy (prep for labor).
  • Increases prolactin production from anterior pituitary.

Cardiovascular and Hematologic Changes

Progesterone

  • Causes smooth muscle relaxation → vasodilation → ↓ SVR.
  • Contributes to increased plasma volume.

Estrogen

  • Increases production of angiotensinogen → helps support plasma volume expansion.
  • Stimulates coagulation factors (↑ risk of DVT/PE).
Increased clotting risk in pregnancy is partly due to estrogen → increased VTE risk.

Respiratory System

Progesterone

  • Increases central respiratory drive → mild respiratory alkalosis (↑ tidal volume).
    • Renal compensation → Metabolic acidosis (Decrease in bicarbonate concentration)
  • Helps to clear excess CO₂ generated from fetus via mother’s lungs.
ABG may show low pCO₂ (respiratory alkalosis) and high pO₂ in normal pregnancy.

CNS and Mood

Progesterone

  • Has sedative effects (acts on GABA-A receptors).
  • Can cause fatigue, mood changes, and even sleep disturbances.

Estrogen

  • Affects mood and cognition.
  • May contribute to emotional lability.
Postpartum mood disorders may relate to rapid hormone withdrawal after delivery.

Breast and Lactation

Progesterone

  • Promotes lobular-alveolar development in the breast.
  • Inhibits milk production during pregnancy (despite high prolactin).

Estrogen

  • Stimulates ductal growth in the breast.
  • Increases prolactin secretion (but milk production is suppressed until after delivery).
After delivery, the drop in progesterone allows prolactin to initiate lactogenesis.

Endocrine & Metabolic Effects

Progesterone

  • Increases insulin resistance (along with placental hormones).
  • Promotes fat deposition and supports fetal nutrient availability.

Estrogen

  • Increases thyroid-binding globulin (TBG) → total T₄ ↑ but free T₄ remains normal.