The In Vitro Fertilization process consists in fertilizing an egg with sperm in an artificial environment -a laboratory-. However, the fertilizing process is completely natural since approximately 50,000 sperm are placed with each egg, which is naturally penetrated by one of them. In this way, embryos are formed and left in the laboratory for 2-5 days to culture and are then transferred into the uterine cavity by means of a catheter; this procedure is very simple and not cruel at all.
This technique originally developed to treat infertility caused by fallopian tube obstruction. However, the indications for the treatment have broadened over the years and all those cases in which the sperm may have a difficult time joining the egg have been incorporated. In this way, male deficiencies, endometriosis, immunological disorders, and infertility due to unknown factors, among others, have been treated and several procedures such as embryo cryopreservation, micro-manipulation techniques, sperm recovery, co-culture, assisted hatching, preimplantational genetic diagnosis, and others, have been incorporated.
1- Controlled ovarian hyperstimulation and ovulation monitoring.
Even though the first cases of IVF were performed during spontaneous cycles; nowadays, the best results are achieved through retrieving a good number of oocytes. In an effort to increase the chances for a pregnancy with IVF, the physician may prescribe medications in order to develop several follicles. Multiple eggs, and therefore multiple embryos, increase the probability of conception. This administration is called controlled ovarian hyperstimulation, since it induces the development of multiple follicles under strict control to avoid possible complications.
Several drugs are used for hyperstimulation. It is very common for physicians to primarily use a medication called GnRH analogue, which reduces the hormone levels in women when used for an extended time, allowing to control the cycle with a different medication. The administration of GnRH analogue typically begins during the cycle prior to fertilization, everyday until follicular aspiration is performed. There are relatively few cases where GnRH analogue is used at the beginning of each menstrual cycle of fertilization. These are called long-term and short-term treatments respectively.
Early in the menstrual cycle, hormones are used on a daily basis to stimulate ovulation. Different types of medication are used to induce ovulation, especially gonadotropins, with several types. The physician prescribes a specific type to each patient (according to age, hormone levels, previous answers, etc.) so, there may be different types for different women.
At some point during the cycle (usually from day 5 on) transvaginal ultrasounds and hormonal testing may be ordered to check ovulation and therefore, adjust the dosage of the medications.
When follicles have grown sufficiently, she will take additional medication (HCG or LH) to complete the egg maturation process. 34 - 38 hours after HCG or LH administration, follicular aspiration is performed.
Even though controlled ovarian hyperstimulation is performed in most cases, the physician may choose not to use any of the fertility drugs described above, in order to obtain one mature egg and therefore, the development of a single embryo. These cycles are known as "spontaneous or natural cycles", generally used to avoid multiple pregnancies or in cases with poor response to ovarian stimulation.
2- Egg Retrieval
Originally, eggs were retrieved through follicular puncture, by inserting a laparoscope into the abdomen under general anesthesia and hospital stay was required. Nowadays, eggs are retrieved by a transvaginal ultrasound-guided aspiration, a method widely used since it requires the use of local and/or general anesthesia and can be performed on ambulatory basis.
In order to do this, the physician first uses local anaesthesia and then a vaginal transducer is placed in the vagina. The ultrasound image allows the physician to locate the follicles, puncture them and then aspirate their content with a needle. Their content is sent to the biologist who will determine if the procedure has been successful. This procedure is performed with every follicle. The average number of eggs retrieved is between 8-9 , and aspiration lasts approximately 20 minutes.
Eggs are not always retrieved from every follicle. Some follicles will not have eggs or will have post mature eggs which may not be capable of being fertilized. Because of this, the number of follicles detected in the ultrasound image is not necessarily the number of eggs that are retrieved.
Once the oocytes have been retrieved, they are tested in the laboratory and classified according to their maturity. During this time, the male partner provides a semen sample where it undergoes a process referred to as swim up or density gradient to separate motile spermatozoa. The sperm are incubated and placed in the petri dish with the eggs at body temperature.
After 18 hours, the oocytes are examined for signs of fertilization. The sign of fertilization is the presence of two polar bodies and two pronuclei. Embryos are normally transferred and left in the laboratory to culture for 48 hours or 72 hours. During this period, the fertilized egg divides to form a multicellular embryo.
4- Embryo Transfer
Embryo transfer is a simple procedure but considerably important. The procedure, carried out on an ambulatory basis, does not require anesthesia and selected embryos are inserted into a thin tube and guided toward the woman's uterus. Transfer typically takes place 3 days after egg retrieval.
The number of embryos to transfer is widely discussed. Some countries limit the number of embryos transferred; however, this generally depends on the characteristics of the embryo and on the age of the woman. Usually, the number is between 3 and 4.
5- Luteal Phase Support
The Luteal Phase is the term used to describe the time period after ovulation. During this phase, an hormone known as progesterone prepares the endometrium for the implantation of the embryo.
Progesterone supplementation is used for patients who received GnRH analogue during follicular phase, since their progesterone levels are generally low. To that end, vaginal capsules / vaginal gels or progesterone injections are used.
Around 14 days after transfer and if menstrual period has not arrived, a pregnancy test is performed. This is a period full of anxiety so you must make an effort to remain calm and perform activities to keep you entertained.
Pregnancy rates using this technique could vary depending on the age of the woman, cause of infertility, eggs quality, number of embryos transferred, and sperm quality, among others. Pregnancy rates are of approximately 25% per cycle started, achieving more that 70% after 4 attempts. These results should be interpreted taking into account that the natural pregnancy rate is of 20 to 30%. In this way, these techniques give couples with a low probability of spontaneous conception (1% per cycle for instance), a chance to be on the same level as natural fertility rate.
However, results may vary depending on several factors such as different centers or time.
Many times, if after undergoing IVF pregnancy does not occur, through investigation, the physician may be able to determine the cause of infertility and in many cases, consider modifications for future attempts.
They tend to be simple procedures involving no risks. The most commonly mentioned risks are ovarian hyperstimulation, multiple pregnancies, ectopic pregnancies, spontaneous abortion, and risks associated with puncture.
However, there is a low percentage of complications. Some risks may be controlled depending on the stimulation carried out; others are controlled by the number of embryos to transfer; and risks such as ectopic pregnancy and abortion depend on external factors.