Intracytoplasmic Sperm Injection (egg is approximately 100µm across, sperm is visible in the injection needle), image courtesy of Dr. Vasil Galat, Lurie Children’s Research Center.
We have already looked at the process of ovulation and fertilization as it occurs in nature (you can read our last couple of posts on the subject here, here, and here). Of course, sometimes for a variety of reasons this process does not occur as it should. In humans a number of conditions can prevent conception in the way we discussed. For farmers it might be better to have more direct control of fertilization among valuable stock animals. A variety of techniques now exist and are commonly practiced to give nature a helping hand in the fertilization process. In aggregate these techniques are referred to as assisted reproductive technologies.
The most common of these is in vitro fertilization or IVF. Basically an egg is obtained from Mom by surgical means (usually with a minimally invasive procedure threading a small needle through a tiny hole in the abdomen, or more commonly through the vaginal wall) to pluck oocytes, or eggs, at near maturity from the ovary. This can be done with ultrasound control or with a tiny camera to guide the surgeon with this harvest. Sperm from Dad is obtained and the two are simply mixed in a dish.
Successful fertilization is monitored by watching for cleavage divisions after putting the dish in an incubator (which is just a sterile cabinet that is body temperature and has an atmosphere that maintains a normal acid/base balance). If an embryo develops successfully from this process it is placed back in the uterus of Mom and can develop normally to term.
When this was first done in humans three decades ago the children were referred to as “test tube babies.” They have grown up and have babies of their own now. More than 60,000 babies a year are born in the US using these techniques and perhaps several million children have been born with IVF techniques worldwide since the first IVF birth in 1978 [For more information on the first IVF birth, the American Experience website has articles associated with their PBS documentary “Test Tube Babies” here]. Whether there is an increased risk of birth defects or poor health outcomes in IVF children remains a controversial issue. If there is an increased risk it seems to be very minor.
Sperm around an oocyte during mouse IVF.
Source: Video S2 from Motosugi N, Dietrich J, Polanski Z, Solter D, Hiiragi T (2006). “Space Asymmetry Directs Preferential Sperm Entry in the Absence of Polarity in the Mouse Oocyte”. PLOS Biology. DOI:10.1371/journal.pbio.0040135. PMID 16620153. PMC: 1440932.
Sometimes infertility is the result of low sperm counts or poorly performing sperm. It usually takes around 100,000 sperm for each egg to have successful fertilization in a dish. When this is not possible or there are other problems with the sperm, modern IVF techniques can overcome these problems. Another tool in the assisted reproductive technology toolbox can overcome these problems, and it’s called intracytoplasmic sperm injection or ICSI [pronounced “ick-see”]. Rather than allowing the sperm to move around in a dish until it encounters the egg, a needle is used to inject the sperm into the egg under a microscope.
Technology continues its advances and offers more options to families with fertility problems or those at a particular risk for inherited disease. We can now screen the health status of the IVF embryo. So-called preimplantation genetic diagnosis (PGD) directly sequences the genome or screens for conditions that pose specific risks to the family in the embryo before it gets transplanted back into Mom. This can rapidly screen for hundreds of genetic disorders.
Using IVF to create human embryos for purely research purposes is considered unacceptable in most societies and is explicitly illegal in many places. Some countries (and some states in the US) have made using IVF as a method to select disease-free embryos illegal. This is a highly contentious matter and the ethics involved are complex. In its simpliest form the issue becomes: Is it right to use IVF and PGD in the absence of infertility to ensure that the child will not have a devastating genetic disease by choosing among several available IVF embryos the ones that do not have evidence of genetic disorders?
As the methodology for determining the genetic health of an embryo advances, the pressure on this ethical argument will grow. Stronger ethical arguments are made against using these methods to select the sex of the child or other attributes, although these are considered acceptable uses in some societies.
- For families struggling with fertility, there are a lot of helpful techniques available that as a collection get referred to as assisted reproductive technologies.
- The most common technique is in vitro fertilization, or IVF, where an unfertilized egg is isolated from the mother which gets put into a dish with sperm from Dad. The fertilized embryo is then transplanted into the mother’s uterus.
- IVF since it’s beginning is responsible for millions of births worldwide.
- If the fertility issue lies with Dad’s sperm, either a low count or motility problems, the sperm can be injected directly into the egg to expedite fertilization. This is called intracytoplasmic sperm injection or ICSI.
- Preimplantation genetic diagnosis screens embryos for inherited diseases from parents that have an increased risk of passing on health problems to their children (like Tay-Sachs disease, Down syndrome, or sickle cell anemia).
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Originally published at lcresearchcenter.tumblr.com.