In vitro fertilization (IVF) is the most common form of assisted reproductive technology (ART) in which sperm is combined with an unfertilized egg outside the body in a laboratory (in vitro, Latin for “in a glass”) to achieve fertilization, resulting in an embryo. The embryo is then transferred into a woman’s uterus (womb) or is cryopreserved (frozen) for future use.
An IVF cycle consists of these basic steps: (click on them for more information below)
- Ovulation Induction
- Egg Retrieval
- Collection and Sperm Preparation
- Insemination, Fertilization and Embryo Development
- Embryo Transfer
- Cryopreservation & Embryo Freezing
Ovulation Induction is a process where fertility medication is administered to stimulate the ovaries to produce multiple mature eggs.
The egg retrieval process is a minor surgical procedure that uses an ultrasonic probe to guide a thin needle through the wall of the vagina into the ovary to collect the mature eggs. The needle penetrates the follicle, where the egg resides in the ovary, aspirating the follicular fluid. The eggs are then identified under a microscope, washed and placed in a culture dish with nutrient fluids. This procedure may last anywhere from 15 to 30 minutes and can done on an outpatient basis under deep sedation to avoid any pain or discomfort.
Collection and sperm preparation is usually done on the day of the egg retrieval. Sperm can either be obtained from the woman’s male partner or from a sperm donor. Sperm used is typically “washed,” separating the sperm from the seminal fluid, increasing the number of mobile sperm and improving the likelihood for fertilization.
Sperm collection can sometimes be stressful for a man. For those men, a semen sample can be produced ahead of time and cryopreserved until needed. In some male factor infertility cases, a testicular biopsy can also be performed as a method to extract sperm for IVF.
In the embryology lab, sperm and egg are then combined to allow fertilization, creating embryo(s). This process is referred to as conventional insemination, allowing the natural process of sperm selection to take place.
When sperm has poor sperm survival, moderate or severe defects and/or a history of poor fertilization from previous IVF cycles, the laboratory will perform intracytoplasmic sperm injection (ICSI). This process involves injecting a single sperm into each egg. This technique greatly increases the chances that fertilization will occur.
Twelve to sixteen hours after conventional insemination or ICSI, the sample is examined to confirm that fertilization has taken place. Fertilization is the union of male and female reproductive cells (gametes- sperm and egg) to produce a fertilized egg (zygote). Once this occurs, the fertilized eggs are considered embryos.
The embryo(s) are then cultured to grow and divide in the laboratory for three to five days before being transferred.
Transferring the embryo(s) is the final and most important step in the IVF process. After three to five days following fertilization, one or more embryos are placed into a woman’s uterus. This step requires the use of a small catheter to draw up the selected embryo(s) and to inject them into the middle of the woman’s uterine cavity. This procedure mimics that of a routine pap smear and has little pain or discomfort associated. For best results, the use of ultrasound technology is used to guide the catheter to the best location within the uterine cavity.
While some centers transfer multiple embryos that can result in multiple births, the UC Center for Reproductive Health follows the American Society of Reproductive Medicine (ASRM) guidelines and typically transfers one to two embryos at a time, thus reducing the likelihood of multiple births. For those patients who qualify we offer single embryo transfer, transferring only one embryo at a time.
Upon completion of transferring the embryo(s), the embryo(s) should “hatch” from their outer shell and implant into the uterine wall. A blood test is performed, typically nine to eleven days after transfer, to determine if a woman is pregnant. If embryo implantation has occurred, the hCG hormone will be detected in the bloodstream and the woman will be considered pregnant.
Assisted hatching is a procedure that is performed in order to help an embryo hatch out of its outer protective layering (zona pellucida) and implant into the uterus. In certain situations the outer shell surrounding the embryo is thickened and/or hardened, therefore not allowing it to “hatch,” or break out, and compromising an embryo’s ability to implant into the uterine wall.
The procedure involves making a small incision into the outer shell just prior to the transfer of the embryo into the uterus. This increases the likelihood that the embryo will implant into the uterine wall, resulting in a successful pregnancy.
Traditionally, embryos are transferred into the uterus three days after fertilization. If a patient has a large number of embryos and/or the best embryos are not clearly identified on day three, we may suggest waiting two more days and doing a blastocyst embryo transfer. The advantage to waiting two extra days to five days before transfer is that it helps provide more information on the quality of embryos and gives a better choice of which embryos to choose for transfer.
During the IVF process, sometimes, more embryos develop than are used or transferred. Should this be the case, there is the option to freeze (cryopreserve) any excess good quality embryos for future IVF attempts. Embryos can be frozen at the pronuclear stage (one cell), or at any stage after that up to and including the blastocyst stage (five to seven days after fertilization).
There are two methods used to freeze embryos:
The slow-freeze method of cryopreservation is the traditional approach of freezing extra embryo(s). While success rates using this technique are excellent, the disadvantage is the accumulation of ice crystals over time which may be damaging to frozen embryos.
The vitrification method is the newest technology in cryopreservation. It is an ultra-rapid freezing technique minimizing any ice crystal formation and potential damage to frozen embryo(s). Research studies have shown better post-thaw survival rates and higher live birth rates using embryo(s) frozen by this technique as opposed to others.
If a patient or couple does not wish to cryopreserve their extra embryos, they may choose to “donate” the embryos.