Menstrual Cycle Review
To understand IVF, it is helpful to understand the normal 28 day menstrual cycle.
Follicular Phase: Days 1-14 of the cycle
Baseline: What we call the condition at the beginning of your period.
- Hormones (estrogen, progesterone and LH) are all at the lowest they will be at any point during the cycle (Estrogen is less than 75, progesterone is less than 2.0, LH is less than 10.).
- Uterine lining is sloughing off so it can start fresh. At this point the lining measures less than 6-7mm.
- Ovaries do not have any significant follicles measuring over 12mm.
- As ovulation approaches, estrogen level increases and uterine lining thickens.
- One of the ovaries produces a dominant follicle, the fluid-filled sac that contains an egg. As the follicle grows from less than 10 mm to about 20 mm, the egg inside is maturing, preparing for ovulation.
Ovulation Occurs When:
- The follicle reaches maturity, approximately 20mm in size.
- The LH level rises dramatically and briefly.
- Estrogen levels taper off.
- The egg inside the follicle matures and loosens from the follicle wall. The follicle itself bursts and the egg is expelled, floating down the fallopian tube, where it will survive approximately 24 hours.
Luteal Phase: Days 15-28 of the cycle
- The egg leaves the ovary and travels down the fallopian tube.
- The estrogen level dips down and the progesterone hormone begins to rise.
- Progesterone is vital to the uterus; specifically the lining of the uterus called the “endometrium.” This lining has been growing thicker with the help of estrogen; however, the addition of progesterone is required to produce the right chemical combination for implantation and growth of an embryo.
- The endometrial lining must provide a hospitable environment for an embryo to nestle in and begin to grow. Estrogen and progesterone are the hormones that make this possible. In very simple terms, estrogen makes the endometrial lining “fluffy;" progesterone makes it “sticky.”
- If the egg meets sperm on the way down the fallopian tube and is successfully fertilized, the newly created embryo will reach the endometrium a few days later and begin to implant.
- The corpus luteum (what had been the follicle containing the egg and is now a cyst) continues the production of progesterone to keep the endometrium thick and healthy.
- The newly implanted embryo will begin to produce another hormone, beta hCG (human chorionic gonadotropin). This is the hormone of pregnancy.
- The raised progesterone level and presence of hCG will keep the lining from sloughing off, thereby delaying the onset of another period.
If no fertilization or implantation occurs, the body will stop production of progesterone. The rapid decrease in progesterone levels is what causes another period to begin. The cycle starts all over again with the onset of the period.
To learn how an IVF cycle works, click here.
Click here or call 800.552.4363 or 703.698.7355 to schedule a fertility consultation at GIVF.