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The Dish on IVF Treatment

July 11, 2018
Katie Visco

Choosing to seek out IVF treatment is an emotional and oftentimes stressful process. You may find yourself lost in the technical terms that you often have to confront when undergoing IVF. Today, we are going to discuss the stages of egg fertilization and implantation so you can understand what is happening behind lab doors. In this article, we will outline:

  • Egg fertilization
  • Embryo growth
  • Embryo transfer

IVF is an important procedure for many women, but it does not have to be elusive.

Egg Fertilization

After eggs have been harvested, they must be fertilized on a petri dish outside the body. The number of eggs harvested depends largely on how your body responded to hormone treatments and your age. Typically, six to 12 eggs are harvested and then put in a medium that emulates fallopian tube fluids. This ensures that eggs begin to develop as if they are still in your body.

Eggs incubate on the dish for four to six hours before being fertilized by sperm collected at the time of egg harvestation. Sperm is assessed for viability, and if it is determined that sperm quality is low or there are other factors that can affect fertilization, ICSI (intracytoplasmic sperm injection) may be used.

ICSI is the process of injecting a single sperm directly into an egg. This is effective because it increases the chance of fertilization by physically bringing the sperm and the egg together.

Depending on your clinic and the quality of sperm, ICSI may not be needed, although many clinics are using it as their standard practice regardless. By doing so, they are increasing the odds of fertilizing as many embryos as possible.

Inseminated eggs are incubated for a few days in a very carefully controlled environment to promote embryo growth.

Embryo Growth

While embryos are still on the dish, their growth and development is carefully monitored. Despite the controlled insemination, not all embryos grow normally or at all. Abnormal embryos are removed while developing embryos continue to be observed. Typically, it takes about five days after fertilization for embryos to be considered blastocysts that are ready for implantation, although younger embryos can also be used. Your doctor should discuss which stage of embryo growth is best for implantation in your situation.

Embryos are assessed by embryologists and graded for their quality. First, they are assessed on the second on third day before the blastocyst stage is reached. Highest quality embryos at this point have a reported implantation rate of 20-35% depending on the woman’s health and age. Blastocysts are graded a few days later on a letter grade scale. High quality blastocysts have a 45-65% chance of resulting in pregnancy.

Embryo Transfer

After your embryos have been assessed, it is time to transfer them to your uterus. The best day for this will be determined by your doctor.

Usually, not all of your embryos are transferred to your uterus at the same time. For most people with embryos of average quality, two to three are used during the transfer process. While chance of pregnancy increases with the number of embryos transferred, so does the risk of multiple pregnancies.

Other factors that affect how many embryos are transferred are age, length of infertility, and previous IVF treatments. If you have quality embryos that are not being transferred, they could potentially be frozen for future use.

If your embryos have a thick membrane, embryologists may use assisted hatching to thin the outer layer of the embryo to increase chance of implantation. Factors that affect embryo membrane thickness are:

  • Being over the age of 38
  • Cryopreservation
  • Undergoing multiple IVF treatments

Once embryos have been chosen and prepared for transfer, they are placed on a catheter and deposited into the uterus. This is a very quick process and you can go about your day afterwards without any problem.


IVF is a very involved process, but understanding what is happening to your eggs in the lab can bring you peace of mind. It is important to remember that the quality of your embryos while they are still on the petri dish does not reflect the quality of future genetic material. Speak to your doctor about any concerns you may have regarding your treatment.


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