Pregnancy and Menopause Overview

Pregnancy and Menopause

• Pregnancy typically lasts approximately 40 weeks.
• During pregnancy, estrogen and progesterone levels increase steadily.
• These hormones maintain the endometrium, develop breast tissue for lactation, and prevent the development of new ovarian follicles.
• In early pregnancy (first trimester), the corpus luteum is the source of steroid hormones.
• In mid-to-late pregnancy (second and third trimesters), the placenta becomes the source of steroid hormones.
• Fertilization of an ovum occurs within 24 hours of ovulation in the ampulla of the oviduct.
• Four days after ovulation, the fertilized ovum (blastocyst) containing approximately 100 cells, enters the uterine cavity.
• The blastocyst implants into the endometrium 5 days after ovulation.
• Implantation depends on the low estrogen-to-progesterone ratio, highest at the time of implantation.
• The blastocyst differentiates into the fetus (inner mass) and trophoblast (outer rim), which is the fetal portion of the placenta.
• The trophoblast invades the endometrium, forming an attachment to the maternal membranes.
• At implantation, the endometrium specializes into decidual cells, enveloping the conceptus.
• The trophoblast cells form the syncytiotrophoblast, aiding the blastocyst's penetration into the endometrium.

Early Fetal Development

• Early development progresses through different stages, including fertilization, zygote, morula, and blastocyst.
• Fertilization occurs 0-1 day after ovulation.
• Zygote forms at fertilization.
• Morula stage (days 2-3).
• Blastocyst stage (days 4-5).
• Implantation (days 6-10).

Secretion of HCG and Rescue of the Corpus Luteum

• The trophoblast secretes Human chorionic gonadotropin (hCG) approximately 8 days after ovulation.
• hCG informs the corpus luteum of fertilization.
• The corpus luteum continues producing progesterone and estrogen under the direction of hCG.
• These hormones maintain the endometrium for implantation.
• Without fertilization, the corpus luteum regresses 12 days after ovulation (menstruation occurs).

Hormones of Pregnancy

• Hormone levels change throughout pregnancy.
• hCG is produced by the trophoblast, peaking around gestational week 9.
• hCG "rescues" the corpus luteum, stimulating progesterone and estrogen production, which maintain the endometrium.
• In the second and third trimesters, the placenta becomes the primary producer of steroid hormones, including progesterone.
• Cholesterol is converted to pregnenolone, then to progesterone in the placenta.
• Estriol, a major estrogen form, is produced through several steps involving the placenta, fetal adrenal cortex, and liver.

Second and Third Trimesters (Placental Production)

• The placenta produces steroid hormones in the second and third trimesters.
• The placenta produces progesterone from cholesterol.
• Cholesterol is converted to pregnenolone, and then progesterone.
• The placenta produces human placental lactogen (hPL), which is structurally similar to GH and prolactin.

Parturition

• Parturition (childbirth) involves multiple factors.
• Estrogen increases uterine contractility, and progesterone decreases it .
• Increasing the estrogen/progesterone ratio increases uterine sensitivity to contractile stimuli.
• Oxytocin facilitates uterine contractions.
• Cortisol, from the fetal adrenal cortex near term, increases estrogen/progesterone ratio.
• Parturition has three stages:
  • The first involves contractions widening and thinning the cervix.
  • The second is the expulsion of the fetus through the vagina.
  • The third stage is placental delivery following expulsion of the fetus.

Lactation

• Estrogen and progesterone stimulate breast growth and development during pregnancy.
• Prolactin levels increase steadily.
• Lactation is inhibited during pregnancy by estrogen and progesterone.
• After childbirth, these hormones decrease, allowing lactation to begin.
• Suckling stimulates oxytocin and prolactin secretion, maintaining lactation.
• Lactation suppresses ovulation.

Hormonal Contraception

• Oral contraceptives primarily inhibit ovulation through negative feedback on the anterior pituitary.
• Progesterone alone can affect cervical mucus and tubal motility.
• Higher doses can inhibit implantation.

Menopause

• Menopause is the cessation of menstrual cycles around age 50.
• Estrogen levels decline.
• Decreased estrogen leads to increased FSH and LH, eventually ceasing menstruation.
• Symptoms include vaginal thinning, reduced secretions, breast changes, bone loss, hot flashes, and emotional instability.
• Hormone replacement therapy is an option for decreasing symptoms.

Explore the fascinating stages of pregnancy and menopause with this quiz. Learn about hormonal changes, fertilization, and implantation, as well as the role of critical hormones during these life stages. Test your knowledge on the key concepts related to women's reproductive health.