In Vitro Fertilization
The Basic Steps of IVF
Insemination & Fertilization
In Vitro Fertilization|
IVF is a method of assisted reproduction in which the man's sperm and the woman's egg are combined in a laboratory dish, where fertilization occurs. The resulting pre-embryo is transferred to the woman's uterus. The basic steps in an IVF treatment cycle are ovulation enhancement (stimulating the development of more than one egg in a cycle), egg harvest, fertilization, embryo culture, and embryo transfer.
IVF is a reasonable choice of treatment for couples with various types of infertility. Initially, it was only used when the woman had blocked, damaged, or absent fallopian tubes (tubal factor infertility). IVF is now also used to circumvent infertility caused by endometriosis or by any one of a number of problems in the male. Many programs use IVF to treat couples who are infertile due to immunologic factors or other unexplained reasons.
The Basic Steps of IVF
During ovulation enhancement, drugs are used to induce the patient's ovaries to grow several mature eggs rather than the single egg that normally develops each month. Since most woman ovulate spontaneously, this phase is often referred to as enhanced follicular recruitment or controlled ovarian hyperstimulation, rather than ovulation induction. Regardless of the terminology, IVF specialists agree that the chances for pregnancy are better if more than one egg is fertilized and transferred to the uterus in a treatment cycle. Depending on the program and the patient, drug type and dosage varies. Most often, the drugs are given over a period of seven to ten days. Drugs currently in use include: clomiphene citrate (Clomid‚, Serophene‚), human menopausal gonadotropin (hCG), and a gonodotropin releasing hormone (GnRH) analog called leuprolide (Lupron‚). Most of these drugs may be used alone or in a combination with others.
Timing is crucial in an IVF treatment cycle. The doctor not only must know what is happening in the woman's ovaries, but also when it happens relative to other events in the cycle. To monitor the development of ovarian follicles, which are fluid-filled sacs where eggs grow, the ovaries are scanned frequently with ultrasound. Blood samples are drawn to measure the serum levels of estrogen and sometimes luteinizing hormone (LH). Estrogen production increases as the follicles develop. LH triggers ovulation.
By interpreting the results of ultrasound and blood tests, the IVF specialist determines the best time to harvest or remove the eggs. When the follicles are almost mature, about a day and a half before ovulation would normally occur, the doctor prescribes an injection of human chorionic gonadotropin (hCG). Since ovulation should occur approximately 36 hours later, the use of hCG allows the doctor to control when ovulation will take place. This control allows the IVF team to be prepared to harvest eggs just before that time. The hCG simulates the woman's natural LH surge, which normally triggers ovulation. This surge also initiates changes in the eggs that allow fertilization when the sperm are later introduced.
Ovulation occurs naturally during some treatment cycles, despite the use of these drugs. This is called spontaneous ovulation. When this happens, the eggs may be lost in the pelvic cavity, and the next step in the treatment cycle must be canceled. In some cases, however, a spontaneous LH surge can be detected by blood and urine test before he eggs are released. Ultrasound can confirm that the eggs are still in their follicles. If they are, the doctor may decide to harvest the eggs earlier than originally scheduled.
In the United States in 1988, the treatment cycle was canceled in roughly one quarter of the IVF cycles. The Society for Assisted Reproductive Technology has recorded this information and reported it in The American Fertility Society's journal. Fertility and Sterility. The woman whose cycles were canceled either had responded poorly to drugs used for ovulation enhancement or had premature, spontaneously occurring LH surges with premature ovulation resulting. Cancellation rates as low as 10 percent have been achieved in some IVF programs using GnRH analogs in combination with other drugs during ovulation enhancement. The analogs are synthetic and modified forms of gonadotropin releasing hormone (GnRH). The naturally- occurring gonadotropin releasing hormone causes the pituitary gland to release the gonadotropins FSH and LH. On the other hand, after the first few days, treatment with the analogs prevents the release of FSH and LH from the pituitary gland during treatment, and thereby prevents premature ovulation.
Egg harvest is usually accomplished by one of two general methods. The first, ultrasound-guided aspiration, is a minor surgical procedure that can be done in the doctor's office with intravenous analgesia. Usually, the ultrasound probe is inserted through the vagina. The probe emits high- frequency sound waves which are translated into images of the pelvic organs that are shown on a monitor screen. When a mature follicle is identified, the specialist guides a needle through the vagina and into the follicle. The egg is removed through the needle by a suction device. This is called aspiration. The needle may also be guided through the abdominal wall or through the bladder into the follicle. These approaches may be necessary if the ovary and its follicles are inaccessible using a needle introduced through the vagina.
Laparoscopy is a surgical procedure usually requiring general anesthesia. In the operating room, a surgeon inserts a laparoscope, a long, thin tube much like a telescope, through an incision below or in the woman's navel. Looking through the laparoscope, the surgeon guides the needle through the abdominal wall into the ovarian follicle. The eggs and follicular fluid are then aspirated.
Insemination, Fertilization, and Embryo Culture
The harvested eggs are examined in a laboratory and each is graded for maturity. The maturity of an egg determines when the sperm will be added to it (insemination). Insemination can be done immediately upon harvest, after several hours, or on the following day.
On the day the eggs are harvested, the partner collects his semen by masturbating. The sperm are separated from the seminal plasma in a process known as washing the sperm. The sperm are mixed with a water-based solution in a test tube. The test tube is then placed in a centrifuge and spun at a high speed. The centrifuge force causes the heavier sperm cells to form a pellet beneath the fluid layer. The fluid layer is carefully removed and replaced with fresh solution. Over the next hour or so, some of the motile sperm swim up into the fluid layer. These sperm are used to inseminate the eggs.
A defined number of sperm is placed with each egg in a separate dish containing IVF culture medium. The dishes are placed in an incubator with a controlled temperature that is the same as the woman's body.
It takes about 18 hours for fertilization to be completed, and about twelve hours later the fertilized cell or pre-embryo divides into two cells. The pre-embryo may divide several times while in the incubator. After 48 hours, when pre-embryos usually consist of two to four cells each, they are ready to be placed into the woman's uterus. This procedure is known as embryo transfer.
This is often done in a clinic or office on an outpatient basis. No anesthesia is used, although some woman may wish to have a mild sedative. The patient lies on a table or bed, usually with her feet in stirrups. Some clinics perform the transfer with the patient in the knee-chest position. Using a vaginal speculum, the doctor exposes the cervix. One or more pre- embryos suspend in a drop of culture medium are drawn into a transfer catheter, a long, thin sterile tube with a syringe on one end. Gently, the doctor guides the tip of the loaded catheter through the cervix and deposits the fluid into the uterine cavity. One or more embryos may be transferred during this procedure. Often, transferred embryos are cryopreserved (frozen) with the intent of thawing and transferring them at a later date. The doctor and patient make the decision to use cryopreservation in advance. The entire transfer procedure usually takes between 10 and 20 minutes. Some doctors recommend bed rest after the transfer.
Among all woman undergoing IVF in the United States in 1988, the rate of pregnancies resulting in live birth was approximately 12 percent per treatment cycle. The pregnancy rate varies from program to program and, from time to time, even within the same program. At present there is no single accepted national standard for computing pregnancy rates.
The harvested eggs are examined under the microscope and graded for maturity. The selected eggs are placed in individual dishes and combined with sperm (insemination). The sperm are prepared in advance in the same manner as for IVF. Some doctors prefer to allow the dishes to sit for about 10 minutes before the transfer, since during this period, the sperm adhere to the zona pellucida (outer layer) of each egg. Many programs load eggs and sperm individually into a catheter and inject them into one or both of the fallopian tubes.
Reprinted with permission from the
American Society for Reproductive Medicine