IVF and ICSI are techniques in the field of assisted reproductive technology. Both techniques can be used to help people with difficulties getting pregnant.
This article is pending medical review.
Written by Yasemin Kaya and Sophie Oppelt
Reviewed by Alizeh Ahsan and Julian Zeegers
Edited by Juliëtte Gossens
Assisted reproductive technologies (ART) are based on egg fertilization taking place in a laboratory setting. To learn about the necessary steps of ART before the fertilization, see our introduction to ART. After the egg cells are retrieved from the follicles in the ovaries, the sperm and egg cells are combined in a laboratory to create an embryo. This fertilization step can be accomplished with different procedures, but the most common ones are in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). Both techniques will be explained in detail and compared below. (1, 2)
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In Vitro Fertilization (IVF)
In IVF, the sperm and egg cells are combined in a culture medium (which is food for cells) in a petri dish. A petri dish is a shallow, circular container with a lid, which is then filled with a fluid or gel (the culture medium) that contains nutrients supporting the growth of the embryo. The components in this culture medium mimic the fluid in the ovarian duct (also called the fallopian tube), which is the natural environment for fertilization.
20 hours after combination of the sperm and egg cells, the petri dish is inspected for fertilized egg cells. All the egg cells that are fertilized by sperm cells and have formed a so-called pronuclear zygote (which is the fertilized egg cell), are selected. After approximately 40 hours, the single egg cell should already have gone through cell division twice, forming a total of four cells (the four-cell stage). At this time, the embryos are assessed for viability, meaning only the embryos that have a high likelihood to develop further are selected.
Around day 5 or 6, pre-implantation genetic testing (PGT) can also be performed if you choose to. During this procedure, the embryo is at the blastocyst stage. A small sample of one or more cells is taken and is screened for genetic abnormalities, to make sure that the embryo is healthy. The testing does not have an effect on the developing embryo. However, when you’ve chosen PGT, the results may take a while. Therefore, the embryo is frozen in the meantime and not transferred directly: this is called a frozen embryo transfer (FET). (1- 4)
Intracytoplasmic Sperm Injection (ICSI)
If the person who is supplying the sperm is considered severely infertile, the sperm movement might be impaired and sperm cells will not be able to fertilize the egg cell in the petri dish. ICSI is a solution to this. During ICSI, a single sperm cell is picked up by a very small needle and is injected directly into the egg cell to fertilize it. Afterwards, the fertilized egg cell is placed in a petri dish and goes through the same further steps as described for IVF above. (1- 3)
After the healthy embryos are selected, one embryo is transferred to the uterus of the carrying person within five to six days. The rest is frozen (90% of embryos survive the freezing process), which can be used in case the first transfer is not successful. A thin, flexible tube (also called a catheter) is inserted through the vagina and cervix into the uterus. Oftentimes, ultrasound is used to make sure the tube is in the correct position. Then, the embryo is placed inside the womb, through the tube. Your doctor will carefully check if the embryo is indeed in the womb and is not still inside the tube. The embryo will implant itself in the inner wall of the uterus, the endometrium.
However, to do so, the endometrium must be in the right stage. Therefore, even after the embryo transfer, the carrying parent has to take medication to support the luteal phase (which is the phase of the menstrual cycle after the embryo transfer). This keeps the environment for implantation of the embryo ideal.
After the embryo implants in the endometrium, it starts to develop. After ten days, the carrying parent’s blood is tested for hCG (human chorionic gonadotropin, which is a hormone that is produced during pregnancy) to confirm pregnancy. (1- 3)
Frozen Embryo Transfer (FET)
If parents choose for PGT or if the first embryo transfer was not successful, the embryos that were frozen are used. The process is the same as the direct embryo transfer as described above, and the embryos will be thawed the morning of the transfer.
The timing of embryo transfer is very important, as the endometrium should be in the right phase and be thickened in order for implantation to occur. This stage can be achieved in two ways: in the “natural” way, the menstrual cycle is monitored and the embryo is transferred at the same time the embryo would implant if the fertilization process occurred naturally (through sex). If the menstrual cycle is not regular, hormone medication is given instead, to prepare the endometrium and regulate the menstrual cycle. (2, 3)
Success Rate of ART
In general, the success rate of ART correlates with the number of ART cycles. One cycle describes the steps as explained in the ART Introduction article, and then the egg fertilization, embryo harvest, and embryo transfer as explained above. The success rate is around 30% after the first cycle and 85% after the twelfth cycle. (5)
Success rates strongly depend on the patient's age: the older you get, the less successful ART cycles are. On average, the treatment success rate also depends on patients’ health status, lifestyle, previous pregnancies, and genetic features. Although there are some good predictors of the outcome of ART treatment, there is no sure-fire way to know whether a given cycle will be successful or not. (4, 5)
Good and honest counseling prior to starting the treatment is fundamental for parents undergoing the ART procedure, so that you’re aware of the overall likelihood that ART will be successful for you, and of the possible risks and failures linked to an unsuccessful cycle.
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Racca A, Drakopoulos P, Neves AR, Polyzos NP. Current Therapeutic Options for Controlled Ovarian Stimulation in Assisted Reproductive Technology. Drugs. 2020;80(10):973-994. DOI: 10.1007/s40265-020-01324-w
Barzier Y. Infertility in men and women. Available from: https://www.medicalnewstoday.com/articles/165748 [Accessed May 25th, 2022]
Castelló D, Motato Y, Basile N, Remohí J, Espejo-Catena M, Meseguer M. How much have we learned from time-lapse in clinical IVF? Mol Hum Reprod. 2016;22(10):719-727. DOI: 10.1093/molehr/gaw056
Gnoth C, Maxrath B, Skonieczny T, Friol K, Godehardt E, Tigges J. Final ART success rates: a 10 years survey. Human Reproduction. 2011;26(8):2239-46. DOI: 10.1093/humrep/der178
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