In vitro fertilization (IVF) refers to fertilizing an egg, with a sperm, outside of the body. Fertilization occurs in a dish in the laboratory, which is why IVF translates to “fertilization in glass”.  The embryos are then grown (cultured) for five to six days in an incubator before being transferred back into the uterus to create a 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 an “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

Ovarian stimulation involves the production of multiple ovarian follicles (fluid-filled sacs that contain the eggs). In a normal menstrual cycle, the ovaries typically produce a single mature egg. In IVF, we aim to grow many mature eggs to optimize a patient’s chances of pregnancy. An ideal egg number is considered to be 8 – 20 eggs but it varies widely depending a patient’s ovarian reserve.

Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are administered by injection to stimulate the ovaries to grow many eggs. These injectable medications are required for 8-14 days (on average 10). 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 17mm in diameter the trigger shot is given (human chorionic gonadotropin (hCG) or triptorelin) 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. The trigger shot is administered by subcutaneous injection 36 hours prior to egg retrieval.

Figure 2: Ultrasound appearance of ovaries following stimulation with follicle stimulating hormone (FSH).

Ultrasound appearance of ovaries

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 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.

Transvaginal egg retrieval for in vitro fertilization

Phase 4: Fertilization and Embryo Culture

Eggs deemed suitable for fertilization (mature) can undergo the process of fertilization, which starts the afternoon of 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 cultured for 5 days prior to embryo transfer and observed regularly 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, time lapse imaging (Embryoscope™) and preimplantation genetic testing. On the 5th day of development the embryo is over 200 cells in size (blastocyst stage). This is the best stage of
development to select embryos that are most likely to lead to pregnancy, and also the stage that cells can be removed for genetic screening (preimplantation genetic testing).

Figure 4: Developmental day 3 and day 5 (blastocyst) embryos.

Fertilization and Embryo Culture  Day 3

Fertilization and Embryo Culture  Day 5

Phase 5: Embryo Transfer

Embryo transfer occurs 5 days after egg retrieval. The timing of embryo transfer is determined by the number of embryos and their quality.  The number of embryos transferred is based on several patient-specific considerations including the 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. 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.

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 injections.

Frequently Asked Questions

What is the difference between IVF and ICSI?

ICSI (intracytoplasmic sperm injection) and “standard” IVF are two different ways of fertilizing the egg. Standard IVF refers to placing the egg in a dish with approximately 50, 000 – 100, 000 sperm and allowing natural fertilization to occur. In order to be a candidate for standard IVF, the sperm quality must be normal. When the sperm is not optimal, an embryologist can select a single sperm for each egg and inject the sperm directly into the egg with a tiny needle – this is called ICSI.

Who needs to do ICSI rather than standard IVF?

A male factor component to infertility is present in up to half of all infertile couples, making it one of the most common causes of infertility. In the past, the only option for many male factor couples was intrauterine insemination (IUI) using donated sperm.

Intracytoplasmic Sperm Injection (ICSI) is performed as a part of an IVF cycle wherein a single sperm is inserted directly into the egg for fertilization. The ICSI procedure does not appear to damage the egg and optimizes fertilization rates in cases where a male factor exists. ICSI was a major advance in the treatment of male infertility, allowing virtually all men to father children, with the first case performed in 1990.

The decision to use ICSI is made in consultation with the couple, physician, and embryologists. At most fertility clinics this decision is made based on the sperm testing at the clinic. However, there are some instances where the semen sample collected at the time of retrieval is not optimal, and ICSI may be recommended at that time.

ICSI is performed on the day of egg (oocyte) retrieval. A sperm sample is provided by the partner, and approximately 4-6 hours after the egg retrieval, individual sperm from this sample are injected into each of the mature eggs (fig 5). Fertilization rates with ICSI are typically about 70-80% of mature (competent) eggs. Of note, standard IVF insemination of eggs should yield the same fertilization rates, but is reserved for cases when the sperm is considered normal and there is no history of poor fertilization with IVF in the past.

Figure 5: Intracytoplasmic sperm injection (ICSI).Figure 5 ICSI


Many times the sperm needed for ICSI are retrieved from the ejaculate; however, men with no sperm can often still produce sperm for ICSI. The sperm can be retrieved directly from the testicles using testicular sperm extraction (TESE) or from the epididymis using percutaneous epididymal sperm aspiration (PESA). Fertilization rates using ICSI are typically high, and pregnancy success rates are higher compared to standard IVF culture when a sperm factor is the cause of infertility.

PCRM pioneered a surgical procedure in Canada called microsurgical testicular sperm extraction (microTESE), for men with a complete absence of sperm (azoospermia). This is possible because of our unique ability to provide reproductive surgery under general anesthesia (as a level 1 surgical centre). In these cases only small numbers of sperm are available from the testicular surgery, such that freezing cannot effectively be performed for future treatments. This fresh sperm is then used to fertilize fresh eggs that have been collected from an IVF cycle which has been synchronized with the microTESE procedure.

Another common reason to use ICSI is for cases planning PGT – preimplantation genetic testing.

Is there a cost difference between standard IVF and ICSI?

Yes. The cost of ICSI is additional to the cost of standard IVF. Please see the price breakdown in our Fees section.

Can I choose to do ICSI on the day of egg retrieval?

No, unless there are unforeseen circumstances, we cannot choose ICSI at the last minute. This is because a number of items including consent forms and laboratory set-up need to be in place ahead of time to allow for ICSI.