Technically, “in vitro fertilization” only refers to the process of fertilizing an egg outside the body. However, the term “IVF” has come to be used to describe the entire treatment cycle.
In natural conception, the fallopian tube provides three functions: it picks up the ovulated egg, it provides an environment in which fertilization can occur and it transports the resulting embryo to the uterus for implantation. In cases where the fallopian tube is not functional or other impediments to fertility are present, the function of the fallopian tube can be replaced by in vitro fertilization (IVF).
IVF is the most technologically advanced and successful form of fertility therapy available. The pregnancy rates associated with IVF are the highest of all fertility treatments across every age bracket. This is because IVF optimizes all of the steps associated with the reproductive process. In a natural cycle, only one egg is ovulated, fertilized and implanted in the uterus. IVF augments these processes by stimulating multiple eggs to grow, fertilizing them directly in the laboratory (in vitro) and placing multiple embryos into the uterus.
The IVF cycle has three phases: ovarian stimulation and egg retrieval; fertilization and embryo culture; and embryo transfer and progesterone support. A description of these three main principles follows.
Phase 1 – Egg Recruitment and Retrieval
The patient receives a series of hormone injections over a period of several weeks to stimulate the ovaries. These hormones stimulate a number of her existing eggs. Note, these are the eggs that would be naturally lost that month – stimulating multiple eggs does not lower the supply of future eggs. The eggs are then retrieved in a quick outpatient procedure, by piercing an ultrasound-guided needle through the vaginal wall.
Phase 3 – Embryo Transfer
Once the eggs have been fertilized, the embryos are maintained in the laboratory before being transferred to the uterus. Typically, embryo transfer takes place after three days. A blastocyst transfer occurs after five days, and in the case of a tubal embryo transfer, the embryos are placed into the fallopian tube 24-48 hours after aspiration.
A fertilized embryo is delivered into the patient’s uterus via a narrow, flexible catheter, in a procedure similar to that used in intrauterine insemination (IUI). Rather than simply being released into the womb, the embryo is precisely placed on the wall of the uterus to increase its chances of survival.
The transfer process is critical to the success of In Vitro Fertilization. If an embryo is not placed in the correct location, or if a uterine contraction causes it to move once it has been placed inside the uterus, the embryo may fail to implant. We have a great deal of experience in this delicate process, and we utilize special catheters and ultrasound to assist us in the transfer. Additionally, the embryo transfer is practiced in advance of the actual procedure. In some circumstances, a tubal embryo transfer may be recommended for patients who do not respond well to traditional embryo transfers.
Within two weeks, a pregnancy test can be used to confirm successful implantation. Progesterone hormone treatment is continued through the first trimester. This keeps the lining of the uterine wall thick enough to nurture the implanted embryo properly.
For a description of the procedure in greater detail, please see The IVF Cycle.