Assisted Reproductive Technology
What is Assisted Reproductive Technology (ART)?
Assisted reproductive technology (ART) refers to the process of surgically removing eggs from a woman’s ovaries, combining them with sperm in the laboratory, and returning them to the woman’s uterus.
The first IVF pregnancy began a new era of scientists learning how to manipulate and support in culture gametes, eggs and sperm, in the laboratory to facilitate reproduction and promote healthy pregnancies. With the first IVF pregnancy, the field of Assisted Reproductive Technologies (“ART”) was started.
One of the most challenging circumstances facing infertility specialists was one that arose if the sperm was so dysfunctional it could not penetrate the shell (zona pellucida) surrounding the egg, even if the sperm were placed touching the egg in the relative safety of an incubator, overnight.
Embryologists tried cutting, slashing, burning (with laser) the egg shell in an effort to successfully introduce a sperm in a timely fashion, to no avail. They even tried attacking the shell with acid. Nothing they tried reliably resulted in normal fertilization. Often more than one sperm would enter the egg. The egg shell normally hardens once the first sperm penetrates it, and the shell protects the cleaving embryo until implantation. Any damage to the outside of the cleaving embryo alerts the patient’s immune system something is wrong, and the embryo is rejected.
Intracytoplasmic Sperm Injection (ICSI) - Fertilizing the Egg
In 1991, Gianpiero Palermo and his team in Belgium, developed the technique for achieving fertilization even with severely dysfunctional, or extremely few, sperm. They created a technique called gamete “micromanipulation” in which hand-drawn glass “micropipettes” and inverted microscopes are used to select individual sperm, and manually insert the sperm into an egg. The opening made by the pipette that inserts the sperm into the egg is so small, the reaction that hardens the egg – also closes the hole. Leaving an intact shell around the cleaving embryo, so that the embryo is not rejected by the host’s immune system as being somehow damaged.
The day after ICSI, the embryologist take the embryos out of the incubator long enough to determine which have fertilized normally. The DNA from both the egg and the sperm are visible within the newly fertilized embryo and are called pro-nuclear bodies. The embryos are referred to as “2PN”s. The genetic signals fuse at 20 hours, which is called “syngomy.” The embryologist generally informs you how many 2PNs you have, or how many embryos fertilized normally. The embryos go back into the incubator for the next several days.
The first cell division should occur at ^24 hours. If it hasn’t occurred by 27 hours, it isn’t going to. On day 2, the embryo is at four cells. The cells keep splitting in two. The embryo doesn’t begin to read its own DNA until day 3, when the embryo is at 8 cells. This the earliest that an embryo could successfully implant, and become a baby. If you have fewer than 5 or 6 x 8C embryos, you might seriously consider taking them out of culture at this stage. Couples generally transfer two, or maybe three embryos back to the mother on day 3. The danger being that if you transfer three, there is approximately 1% chance that all three will implant - resulting in a triplet pregnancy.
Only 30% - 40% of 8 cell (8C) embryos, left in culture will go on to successfully develop into blastocysts on day 5 of culture. That is the other time in an IVF cycle that an embryo transfer (ET) might occur. Most people would rather wait and do the ET later, because there is “natural selection” going on, and the embryos that make it to day 5 are more likely to succeed.
Embryo Biopsy / Preimplantation Genetic Screening
One of the earliest recognized advantages of having embryos in culture prior to implantation was genetic screening. Before our knowledge of embryo culturing even allowed taking embryos beyond day 3, embryologists would tease 1 of 8 cells (called a “blastomere”) out of the embryo through a small hole they would make in the shell (zona pellucida) with a laser. Removing one eighth of embryonic DNA at that stage in development did not seem to cause any problems, the embryos would continue to develop normally. Geneticists developed techniques to identify specific pieces (sequences) of the DNA of interest to them by a process called “Fluorescent In situ Hybridization” (FISH). This allowed them to know which embryos had a mutation that caused a disease, and exclude that embryo from being transferred.
With advances in culturing technique, once we could reliably culture to day 5, we began being able to take cells destined to be placental tissue, called “trophectoderm.” This allows us to not need to remove the DNA from the embryo itself. A process called “array comparative genomic hybridization” (array cGH) allows us to compare an embryo’s DNA to a standard of DNA known to be normal, and determine overnight if the embryo has aneuploidy (too much or too little DNA). This allows us to prevent unbalanced chromosomal abnormalities such as Down’s Syndrome.
With a technology called Next Generation Sequencing (NGS) we look at the precise order of nucleotides within a DNA molecule, essentially “spell checking” a chromosome, and being able to detect chromosomal abnormalities even at that level.
Advances in knowledge of our genetics, in large part due to the Human Genome Project, have been phenomenal. With a sample of blood, two weeks and approximately $300, anyone can have their genetic code checked and be told if they have anyone of 288 mutations that are known to lead to a disease, including Cystic Fibrosis. This is your “carrier status.” If there are mutations that could lead to significant disease, they will test the other partner. If there is a match, we can screen your embryos and drop the risk of that disease out of your pedigree. With this technology, we can prevent diseases that we currently cannot treat.
Elective Single Embryo Transfer (eSET)
Another advantage of testing the embryo to know that it is genetically normal is that transferring a single embryo can result in a live birth rate of 65%! In its infancy, doctors would transfer many embryos hoping one was going to land in the right place to successfully implant and have the correct DNA to allow development of the pregnancy to the point of having a healthy baby. Transferring too many embryos led to the early IVF era complications arising from sometimes having too many embryos implant. Most of the complications of early IVF were the result of high multiple gestations and premature delivery.
Once can apply these technologies on a large scale to more and more couples, we will be able to select only healthy embryos for transfer, and maybe eliminate some of the genetically derived conditions that that we currently are not able to successfully treat.