In Vitro Fertilization
Couples who become candidates for in vitro fertilization (IVF) often do so if all other treatments, such as IUI have failed. However, sometimes a precondition such as tubal disease, advanced age, or severe male factor infertility makes IVF treatment the only option available.
In vitro fertilization (IVF) means “fertilization in glass” or the laboratory. It is a sequential process by which one or more eggs (oocytes) are retrieved from the ovary, fertilized in the laboratory with sperm from the male partner and cultured into early embryos. A select number of the resulting embryos are then transferred to the uterus for implantation and pregnancy. There are 6 phases of an IVF cycle: pituitary suppression, ovarian stimulation, egg retrieval, fertilization, embryo transfer and luteal phase support.
Phase 1: Pituitary Suppression
Medications called GnRH agonists (Lupron) and GnRH antagonists (Orgalutran or Cetrotide) are used to inhibit production of the ovulatory hormone luteinizing hormone (LH) from the pituitary gland in the brain, to protect from a “LH surge” and premature ovulation. If a premature LH secretion occurs, the eggs could be lost from the ovary prior to the egg retrieval (ovulation), and the lining of the uterus (endometrium) put “out of phase” relative to the developmental stage of the embryos generated from the cycle, with failure to implant in the uterus.
Phase 2: Ovarian Stimulation
This phase involves the production of multiple ovarian follicles (fluid-filled structures that contain the eggs). In a normal menstrual cycle, the ovaries typically produce a single mature egg. In order to maximize the patient’s chance of pregnancy, follicle stimulating hormone (FSH) and luteinizing hormone (LH) are administered by injection to stimulate the production of between 10 and 20 eggs from the ovary. These medications are required for 9-14 days (on average 12). The follicular development is monitored by a series of transvaginal ultrasounds and estradiol (E2) levels (fig 2). Once there are at least 2-3 follicles measuring at least 18mm in diameter, human chorionic gonadotropin (hCG) is given to re-initiate meiotic development within the eggs (clinically referred to as maturation) and loosen the egg complex from the follicle wall to facilitate extraction during the egg retrieval procedure. HCG also serves to stimulate progesterone production from the ovary (corpus luteum generated at each follicle site) and thus provides luteal phase support for the implanting embryo and subsequent pregnancy. HCG is administered by subcutaneous injection 36 hours prior to egg retrieval.
Figure 2: Ultrasound appearance of ovaries following stimulation with follicle stimulating hormone (FSH).
Phase 3: Egg Retrieval
Egg retrieval is an ultrasound-guided needle aspiration procedure to drain the follicular fluid from the ovary (fig 3). Most are performed under conscious (twilight) intravenous sedation using an opioid and benzodiazepine (fentanyl and midazolam). The fluid is then examined under a microscope by the embryology staff. Once eggs are located they are cultured in an incubator until the time of insemination or ICSI approximately 4 hours later, as described below.
Figure 3: Transvaginal egg retrieval for in vitro fertilization.
Phase 4: Fertilization and Embryo Culture
Eggs suitable for fertilization (mature) can undergo the process of fertilization, which starts the afternoon of the egg retrieval. Embryology staff process the semen specimen provided by the male partner or donor and either perform standard IVF insemination by adding approximately 50,000 sperm to eggs in a culture dish, or directly inject the mature eggs with a single sperm through the process of intracytoplasmic sperm injection (ICSI). The eggs are examined the next morning for evidence of fertilization, at which time they are termed zygotes, or a single-cell embryo. Embryos are typically cultured for 3 to 5 days prior to embryo transfer and observed daily to follow their growth and appearance (fig 4). Various methods are used to assess the “quality” of the embryos. At PCRM we use a combination of visual grading under a microscope, and the latest method of following embryo development, time lapse imaging (Embryoscope™). The majority of cases are cultured to the 5th day of development, when the embryo is over 100 cells in size (blastocyst stage). This is the best stage of
development to select embryos that are most likely to provide for pregnancy, and also the stage that cells can be removed for genetic screening (preimplantation genetic screening/comprehensive chromosomal screening).
Figure 4: Developmental day 3 and day 5 (blastocyst) embryos.
Phase 5: Embryo Transfer
Embryo transfer occurs 3 or 5 days following egg retrieval. Timing of embryo transfer is determined by the number of embryos and their quality. With Preimplantation Genetic Diagnosis (PGD) and Comprehensive Chromosomal Screening (CCS) only embryos that are tested as normal qualify for transfer. The number of embryos transferred is based on several patient specific considerations including age of female partner, quality of embryos, past fertility history, and very importantly, the implantation rate (probability of each embryo developing in the uterus) of the particular clinic. The patient is requested to have a full bladder so that transfer may be visualized using ultrasound guidance and also helps straighten the uterus in patients with an anteversion (80% of women). The embryos are loaded into a soft, flexible catheter attached to a syringe and passed through the cervix into the uterus (fig 5). Gentle pressure is then applied to the catheter syringe and the embryos are released into the uterus.
Figure 5: Ultrasound-guided embryo transfer.
Phase 6: Luteal Phase Support
The IVF process requires the supplementation of progesterone to support the endometrial lining at the time of implantation and early pregnancy. Following the pituitary gland suppression that is required for treatments like IVF, endogenous production of progesterone can be inadequate and result in a luteal support deficiency and pregnancy loss. As mentioned previously, hCG stimulates progesterone production from the ovaries, and combined with a long half-life (48 hours) in the circulation, provides for an excellent form of luteal phase support. Progesterone supplementation is most commonly given as either vaginal suppositories or intramuscular injection.