IB Biology Topic D3.1.7: Use of Hormones in in Vitro Fertilization (IVF) Treatment Notes

Hormones Give Doctors Control Over Egg Production and Fertilization in IVF

1. In vitro fertilization (IVF) fertilizes eggs outside the body, then transfers an embryo to the uterus.
2. Hormones let doctors override the natural cycle so they can collect several eggs at a predictable time.

A Natural Cycle Releases One Egg, So IVF Uses Hormones to Get More

1. In a natural menstrual cycle, a woman usually releases only one egg per month.
2. IVF works better with multiple eggs, which raises the chance of successful fertilization.
3. Suppress the natural cycle so doctors control the timing of egg release.
4. Stimulate the ovaries to grow several eggs at once, called superovulation.
5. Prepare the uterus lining so an embryo can implant.

IVF Hormone Treatment Runs in Five Ordered Steps

Step 1 Down-Regulation: Switching Off the Natural Cycle

1. A GnRH agonist is given by injection or nasal spray to shut down the natural cycle.
2. It stops the pituitary gland from releasing FSH and LH.
3. Without FSH and LH, the ovaries stop making oestradiol and progesterone, so the cycle halts.

Step 2 Superovulation: Growing Many Eggs at Once

1. With the natural cycle suppressed, high doses of FSH are injected daily for about 7 to 12 days.
2. This raises FSH above natural levels, so many follicles develop at once, each holding an egg.

Step 3 Maturation: Triggering the Final Ripening of Eggs

1. When the follicles reach about 18 mm across, an injection of human chorionic gonadotropin (hCG) is given.
2. hCG mimics the natural surge of LH, triggering the final maturation of the eggs.

Step 4 Egg Collection and Fertilization

1. Eggs are collected from the follicles with a needle guided by ultrasound.
2. This minor procedure happens 34 to 35 hours after the hCG injection.
3. The eggs are mixed with sperm in a dish and kept at 37 degrees C.
4. If fertilization succeeds, the resulting embryos start to develop.

Step 5 Embryo Transfer and Uterine Support

1. One or more embryos are placed into the uterus when they are about 48 hours old.
2. Because the natural cycle was suppressed, progesterone is given to maintain the uterine lining and support implantation.

Superovulation Raises the Odds by Producing Spare Eggs and Embryos

1. More eggs mean a higher chance that at least one is fertilized.
2. Several embryos can be checked for quality, so the healthiest one is chosen for transfer.
3. Spare embryos can be frozen for later cycles, avoiding repeat egg collection.

IVF Raises Ethical Questions About Embryos, Access, and Donors

1. Embryo fate: what should happen to unused embryos.
2. Access: whether IVF should be available to everyone despite its high cost.
3. Egg donation: how to protect the safety and fair treatment of donors.

Recap: Four Hormones Do Four Jobs in IVF

1. GnRH agonist suppresses the natural cycle through down-regulation.
2. FSH drives superovulation, growing many follicles.
3. hCG mimics the LH surge to trigger final egg maturation.
4. Progesterone supports the uterine lining for implantation.