In order to understand assisted reproduction and how it can help infertile couples, it is important to understand how conception takes place naturally. In order for traditional conception to occur, the man must ejaculate his semen, the fluid containing the sperm, into the woman’s vagina near the time of ovulation, when her ovary releases an egg. Following ovulation, the egg is picked up by one of the fallopian tubes. Since fertilization usually takes place inside the fallopian tube, the man’s sperm must be capable of swimming through the vagina and cervical mucus, up the cervical canal into the uterus, and up into the fallopian tube, where it must attach to and penetrate the egg in order to fertilize it. The fertilized egg continues traveling to the uterus and implants in the uterine lining, where it grows and matures. If all goes well, a child is born approximately nine months later.
IVF is a method of assisted reproduction in which a man’s sperm and a woman’s eggs are combined outside of the body in a laboratory dish. If fertilization occurs, the resulting embryos are transferred to the woman’s uterus, where one or more may implant in the uterine lining and develop. The basic steps in an IVF treatment cycle are ovarian stimulation, egg retrieval, insemination, fertilization, embryo culture, and embryo transfer
Ovulation drugs or “fertility drugs,” are used to stimulate the ovaries to produce multiple eggs rather than the single egg that normally develops each month. Multiple eggs are needed because some eggs will not fertilize or develop normally after egg retrieval. Pregnancy rates are higher when more than one egg is fertilized and transferred to the uterus during an IVF treatment cycle. Timing is crucial in an IVF cycle. The ovaries are evaluated during treatment with vaginal ultrasound examinations to monitor the development of ovarian follicles When the ovaries are ready, hCG or other medications are given. The hCG replaces the woman’s natural LH surge andhelps the eggs to mature so they may be capable of being fertilized. The eggs are retrieved before ovulation occurs, usually 34 to 36 hours after the hCG injection is given. However, 10% to 20% of cycles are cancelled prior to the hCG injection. IVF cycles may be cancelled for a variety of reasons, usually due to an inadequate number of follicles developing. Occasionally, a cycle may be cancelled to reduce the risk of severe ovarian hyperstimulation syndrome (OHSS).
Egg retrieval is usually accomplished by transvaginal ultrasound aspiration, a minor surgical procedure that can be performed in the physician’s office or outpatient center. Some form of anesthesia is generally administered. An ultrasound probe is inserted into the vagina to identify the mature follicles, and a needle is guided through the vagina and into the follicles. The eggs are aspirated (removed) from the follicles through the needle connected to a suction device.
After the eggs are retrieved, they are examined in the laboratory. The best quality, mature eggs (Figure 4) are placed in IVF culture medium and transferred to an incubator to await fertilization by the sperm. Sperm are separated from the semen in a process known as sperm preparation. Motile sperm are then placed together with the eggs, in a process called insemination, and stored in an incubator. When rates of fertilization are expected to be poor, fertilization may be achieved in the IVF laboratory using specialized micromanipulation techniques. Intracytoplasmic sperm injection (ICSI), which a single sperm is injected directly into the egg in an attempt to achieve fertilization Approximately 40% to 70% of the mature eggs will fertilize after insemination or ICSI. Lower rates may occur if the sperm and/or egg quality are poor. Occasionally, fertilization does not occur at all. Two days after the egg retrieval, the fertilized egg has divided to become a 2-to 4-cell embryo. Embryos may be transferred to the uterus at any time between one to six days after the egg retrieval. If successful development continues in the uterus, the embryo hatches from the surrounding zona pellucida and implants into the lining of the uterus approximately six to 10 days after the egg retrieval.