A Step-by-Step Guide to Embryo Creation

Eran Amir

CEO and Founder of GoStork

When natural conception is not possible, embryos are created through in-vitro fertilization (IVF). IVF is a method of assisted reproduction where the egg (from the intended mother or a donor) is combined with sperm (from the intended father or a donor) in a laboratory dish. Following this, once the egg fertilizes and begins cell division, an embryo is formed. This resulting embryo is then either transferred to the uterus (the intended mother’s or a gestational carrier, if you’re doing surrogacy) or frozen for a later transfer. At this stage, you’ll also have the option to test your embryos to check for any chromosomal abnormalities or serious genetic conditions. In this article, we’ll go over the steps involved to create your embryos, whether you’re doing IVF only or preparing for a surrogacy journey.

Embryo creation using own eggs and sperm

IVF involves multiple steps over a four to six week period. As the Society for Assisted Reproductive Technology (SART) explains, the procedure begins in the month prior to the actual IVF. At this stage, the patient may be prescribed oral contraceptives and ovulation suppressors. Some clinics perform a ‘mock transfer’ to identify any potential problems in embryo transfer. Provided all is well, you’ll then be able to proceed to the actual steps of the IVF process:

1. Ovarian Stimulation – the patient is prescribed medication to grow multiple eggs. The higher number of eggs the better, as this increases your chances of fertilization later on in the treatment. If you’re the patient/intended mother, during this time, you’ll visit the fertility clinic regularly for transvaginal ultrasounds and blood tests to check on your ovaries and monitor your hormone levels. Depending on your results, your doctor might adjust medication doses to improve follicular development while at the same time avoiding hyper ovarian response. The greater the number of follicles, the more potential you have of releasing more eggs, increasing the chance that one of those eggs will eventually fertilize and result in a healthy pregnancy. However, overstimulation can lead to health complications, so monitoring is important. Prior to the egg retrieval, and once your follicles have reached 18-20mm in diameter, you’ll receive a hormone trigger injection to stimulate the final maturation of the oocytes.

2. Egg Retrieval – 34 to 36 hours after the hormone trigger injection has been administered, the eggs are removed from the ovary under ultrasound guidance. This is generally done as an outpatient surgery in your doctor’s office. Anesthesia is provided to avoid any discomfort. As SART explains, ‘it’s not uncommon to have some vaginal spotting and lower abdominal discomfort for several days following the procedure’, but this resolves in a couple of days. On average, 8 to 15 oocytes are retrieved.

3. Collect Sperm – Different clinics follow different protocols for sperm collection – some programs require the male partner to take an antibiotic before sperm collection. The most frequent method used for sperm collection is masturbation on the day of the egg retrieval. In cases where the man is unable to ejaculate or has no sperm in his semen, a urologist can obtain usable sperm through a surgical procedure. Some clinics recommend freezing a sperm sample in case the quality of the sperm obtained on the day of the egg retrieval is not optimal.

4. Fertilization – The eggs retrieved are then transferred to the embryology lab. After a few hours, sperm are either placed with the eggs or individual sperm are injected into each mature egg. This technique is called intracytoplasmic sperm injection (ICSI) and is used in cases of male factor infertility. The eggs are then monitored to check for signs of fertilization and subsequently for embryo growth:
– One day after insemination: the fertilized egg is a single cell with two nuclei (zygote)
– Two days after insemination: a normal embryo divides into about four cells
– Three days after insemination: normally developing embryos contain about eight cells
– Five days after insemination: normally developing embryos develop to the blastocyst stage (typified by an embryo that has 80 or more cells, an inner fluid cavity, and a small cluster of cells called the inner cell mass.)

5. Embryo testing – At the blastocyst stage, you have the option to test your embryos. Pre-implantation Genetic Testing for Monogenic Diseases (PGT-M) is for patients who may be carriers of or who have a genetic condition, or those who have a family history of a specific genetic condition like Huntington’s Disease, Tay-Sachs, or Cystic Fibrosis. Pre-implantation Genetic Testing for Aneuploidy (PGT-A) provides information on the embryo’s genetic health, specifically the number of chromosomes. Following the biopsy, the embryos are frozen. The report helps your doctor determine which embryos to transfer. You can learn more about vitrification and genetic testing in “Maximizing Your Chances of IVF Success: Genetic Testing’.

6. Embryo Transfer – If you decide to skip genetic testing, the embryo is transferred to the uterus 3-5 days after egg retrieval. The embryo is placed in the uterine cavity using a thin tube. The procedure does not require anesthesia and you can leave your doctor’s office after a brief recovery period. Remaining embryos can be frozen for a future embryo transfer.

You can learn more about IVF, timelines to expect and costs in our article The IVF Process: A Step-by-Step Guide.

Embryo creation with donor egg or sperm

In a Donor Egg IVF cycle, another woman’s (ie. an egg donor’s) eggs and the father’s sperm are used to create the embryos. The best embryo (which you can also genetically test, as described above) is then transferred to the intended mother, or in the case of surrogacy, to the gestational carrier. While the intended mother will not be genetically related to the child, if she carries, she will still have a significant impact on the development and future health of her baby. Studies have shown that the uterine environment plays an important role in fetal brain development, childhood metabolism and immune health, among other factors. This is explained by epigenetics – the study of heritable phenotype changes that do not involve alterations in the DNA sequence but which can change how the body reads a DNA sequence. This means that even if the genes come from a donor, the intended mother will have a great influence on how those genes work during the baby’s lifetime.

Same sex male couples will also need an egg donor to create their embryos.

There are two donor egg options: fresh and frozen. Data from the Centers for Disease Control and Prevention (CDC) shows that the chances of a live birth with fresh embryos from fresh eggs is higher than that of fresh embryos created from frozen eggs. While a fresh egg cycle is more expensive, it can potentially give you more eggs (10-20) compared to a typical cohort purchase of 6-8 frozen eggs, and thus a higher chance for success or a future sibling journey. You can find more information about the pros and cons of each option in the article The Egg Question: Fresh vs Frozen Donor Eggs?

Once an egg donor is selected by the intended parents and agrees to the match – and prior to starting the egg donation process – the egg donor undergoes a thorough medical screening to ensure that she is fit to receive the stimulation medication required. Her egg reserve is assessed, and her medical history and family and genetic history evaluated. Blood tests are done to check for undiagnosed medical conditions or infectious diseases. Once the egg donor is cleared by the clinic, she is prescribed hormone medications to stimulate ovulation and the production of multiple eggs. The next step is the egg retrieval and fertilization with sperm from the intended father or a sperm donor. The resulting embryo(s) can be frozen for later use or transferred to the intended mother’s uterus. Our article Egg Donation 101 details the whole process.

For IVF patients using donor sperm, the sperm is thawed at the time of the egg retrieval. Again, the resulting embryo(s) can be transferred to the intended mother’s uterus, or frozen for later use.

Embryo creation for surrogacy

In surrogacy journeys, the embryo is created using an egg from the intended mother or a donor and the sperm from the intended father or a donor. The embryo is then transferred to the gestational carrier in a fresh IVF cycle, or in a frozen embryo transfer from a prior ‘freeze-all’ cycle.

Ideally – and to increase your chances of success – you have more than one embryo available. If the transfer to the gestational carrier is not successful, you will need to undergo another IVF cycle to create more embryos.

Embryo adoption

Some IVF cycles may result in more embryos than needed. In such cases, the biological parents may decide to donate them to others working to grow their family.

Embryo adoption is an option for couples with untreatable infertility, recurrent pregnancy loss related to embryo quality, and genetic disorders affecting one or both partners.

Many embryo adoption agencies treat the process similarly to a regular adoption. The agency may require a background and psychological evaluation before the donating family agrees to the adoption.

As the ASRM notes, ‘success rates with embryo donation depend on the quality of the embryos at the time they were frozen, the age of the woman who provided the eggs and the number of embryos transferred’.

Frozen Embryo Transfer

Once you have your embryos, the intended mother or gestational carrier will go through a frozen embryo cycle. The embryo is thawed and implanted into the uterus. You will know if the transfer has been successful around 10 days after – during a period commonly known as ‘the two week wait’. You can read more about this time in Erin Bulcao’s (@mybeautifulblunder) powerful GoStork guest blog post The Two Week Wait.

If the transfer was successful, the pregnancy is closely monitored to identify miscarriage or an ectopic pregnancy. Patients are then generally released to their OBGYN at around 8 -10 weeks gestation.

Remaining Embryos

It’s possible that you will have remaining embryos in storage after a successful transfer. You can keep them to grow your family at a later time, or keep them frozen until you’ve decided the future of your family. The embryos can stay frozen (with an associated fee) until you decide to use them or otherwise. As Circle Surrogacy notes, you have four choices for your frozen embryos:
– Keep embryos frozen indefinitely
– Consent to discard them
– Donate your embryos, either anonymously or directly to a couple or individual you know, as outlined in an earlier section of this article
– Donate them to research
These decisions can be difficult; it’s important to prepare yourself by knowing your options.

In Conclusion

While the main stages of IVF are common to all, the exact procedures followed to create your embryos will depend on your specific case and history. It’s important to communicate with your fertility clinic to identify the best path for you and, as you look through your options, know that GoStork is here to support you with any resources you need.