How IVF Works - What Happens Backstage in a Fertility Lab

Have you ever wondered how the magic happens in the lab when using IVF to get pregnant?  As part of a new Chicagoland Doulas blog series, we’ll be talking with different experts in fields of pregnancy, fertility, postpartum, and prenatal. First up, we’ll be posting a three-part interview with embryologist and embryology lab manager Rachel Watterson. First part of the series is How IVF Works: A break down of embryology, what it entails, and the science behind making babies.

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Rachel, give us an overview of your job as an embryologist and embryology lab manager.

Embryology is the study of embryos...actually the study of gametes, which are sperm and eggs separately all the way through blastocyst formation. Blastocyst formation is day five or six after eggs have been fertilized. What I do as an embryologist and lab manager is help stimulate women to go through In Vitro Fertilization (IVF).

The human body naturally brings up a whole cohort of follicles on your ovaries every month. Your hormones choose one follicle that’s going to ovulate for that month. The medication we stimulate women with shuts down the body's ability to choose just one. That way, we can have multiple eggs for one retrieval. Some people worry that this process would deplete your ovarian reserve. In reality, what happens when the body chooses one follicle, is the rest of them die off anyway. It depends on your age, but in our younger years I would say females go through 20 eggs a month. Most of them just get "trashed." You’re born with the number of eggs you’re going to have your entire life, and it’s about 400,000. What we do is utilize the eggs that are going to get trashed anyway by the body.

We grow as many eggs as we can. After so many days of medication to help grow these embryos, we use a different medication to program your body to ovulate. Then, you go through an egg retrieval.


Egg retrieval is something beneficial to many people who might want to have a baby one day. What is the process like?

The patient is put to sleep, and the doctor uses an ultrasound probe to look at the ovaries while they aspirate the eggs off of the follicles.The eggs are protected in these sacks of fluid on your ovaries, so what they do is suck all of the fluid out and then hand the tubes to me. I look through them to try and find all of the eggs. I clean them off, see if they’re mature and have a chance of fertilization, and we keep the ones that do.

Next, the male “collects.” We clean off the sperm to just get the raw sample. Several hours later we do a procedure called Intracytoplasmic Sperm Injection. We hold on to an one egg and inject a single sperm. Eighteen hours after we do this, we check for fertilization. Only so many fertilize normally. We grow them out of the blastocyst phase, which weeds out the weaker embryos. We’re left with only high quality ones that have a high chance of implantation. We either transfer a good embryo back and freeze the rest, or, if your estrogen gets too high during stimulation, we freeze all then come back and do them later. That’s also the stage when we can do genetic testing to find out if there is theoretically anything chromosomally abnormal with the embryos. If the patients want to do sex selection that’s how we do that. If patients have a known disease in their family we can weed out those, too.

What does a a regular work day look like for you?

If I only have one procedure that day, I go into the lab and check all of the instrumentation to make sure it’s all good to go. If I had a patient the day before, the very first thing I would do is check for fertilization, because it is such a specific time frame. Fertilization can occur anywhere between 12 and 20 hours after you do the injection process. They appear and then disappear, so we try and catch them between 16 and 18 hours,. There are two signs of fertilization from one egg. You should see two pronuclei because one comes from the maternal, and one forms from the paternal. Fertilized eggs also form two polar bodies, which are between the shell of the egg and the cytoplasm. Those pronuclei form and then disappear. They can all do that at different times, because the eggs and embryos grow at different times. Similar but still, if one fertilized at 12 hours after I injected, it could be that those signs disappear by the time I check.

The biggest concern is if eggs fertilize abnormally and have more than two pronuclei, that means they’re an aneuploidy. An aneuploidy is any time there is an abnormal number of chromosomes, whether too many or too few. In a case where there is 3 pronuclei (3PN) instead of two, it’s because the egg had two sets of genetics, because we’re only injecting one sperm. If you don’t catch that at the first stage, then you wouldn’t know and you could potentially be transferring back an abnormal embryo.

After an egg retrieval, I clean off the eggs immediately, sperm I usually clean off within an hour and prep it. Then everything sits in the incubator for 3-6 hours until we’re ready to inject the egg and attempt to fertilize them. Then it’s the 16 to 18 hours after that where it’s the most crucial point.

Keep an eye out for the second part of Rachel’s interview - coming soon!!

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