First comes identifying the appropriate specimen, and then the team takes it through a series of “washings” in special media to remove all the seminal fluid and isolate the sperm (pretty much like it’s done for an intrauterine insemination). As the eggs are prepped, the sperm specimen is kept in an incubator until it’s time to either inseminate the eggs by conventional methods or by going a little bit more high tech.
Conventional sperm insemination
If your partner’s sperm is normal and your eggs are going to be fertilized in the lab with normal insemination, the next steps are as follows:- The sperm are washed, and the egg is separated from the follicular fluid. It still has its cumulus, which helps to activate the sperm.
- For standard IVF, your eggs (up to six to eight per dish) and sperm are placed a in dish that has wells so that each egg, or at most a couple, have its own chamber. This step used to take place in a petri dish, a flat-bottomed round glass or plastic dish, which was labeled with your name, lab number, the date, and the number of eggs in the dish. This is so passé today.
- The dish is placed in an incubator so the eggs and sperm can be kept at body temperature. They’re kept in a nutrient solution (culture medium), which provides conditions as similar as possible to those in the body. Different labs use different culture media, and this is one way that labs differ from one another. However, today most labs purchase their media from a limited number of companies and there are only a few different types of media, so the media is standardized across the industry.
- Conventionally inseminated eggs are left alone for 16 to 20 hours.
- The day after the retrieval, embryology takes the dish out of the incubator, strips off the cumulus (which has by now been greatly loosened by the action of the sperm), and checks the eggs. What they hope to find is two pronuclear (2PN) embryos, or embryos that have two visible circles lined up next to each other. These embryos contain the genetic material from each parent.
Kathryn BornA 2PN (pronuclear) embryo.
High-tech sperm injection
Since the advent of intracytoplasmic sperm injection (ICSI) the use of conventional insemination has decreased significantly. A report by the CDC states that from 1996 to 2012, the use of ICSI for male factor infertility rose from 76 percent to 93 percent and for couples without male factor from 15 percent to 66 percent. Using ICSI for male factor increases the chance that the egg will fertilize. Some men with male factor have sperm that can’t penetrate the shell of the egg, and ICSI bypasses this problem. So, the use of ICSI for male factor makes sense. For couples with no male factor there is less of a need to do ICSI. The problem is that there is no test that accurately identifies the man with a normal semen analysis where his sperm can’t fertilize the egg. The couple undergoes the entre IVF process, places the sperm and eggs together, and the next day finds that none of the eggs fertilized. This is not common but extremely disappointing when it occurs. For that reason, many IVF programs have significantly increased the use of ICSI.If you’re planning to freeze some or all of your embryos for use at another time, your clinic may freeze them at the 2PN stage. Some centers grow all your embryos out to blastocyst stage and freeze only those that make it to blastocyst.