Your Embryo's First 5 Days

Your Embryo's First 5 Days

February 14, 2019
min read

The pivotal moments in any in vitro fertilization (IVF) cycle happen post-egg collection and fertilization. Our exceptional IVF embryology lab is crucial in achieving our impressive success rates from frozen-thawed embryo transfers (FET).

The first five days of an embryo’s development in the lab is an essential phase in the IVF process, where it transitions from a fertilized egg to a structure ready for implantation. In this blog, we will take you through this incredible journey, highlighting the expert care our embryologists ensure throughout the process. 

Day 0: The Beginning of Life

We start the IVF process with the egg collection procedure, carried out under light sedation. Using fertility injections, we stimulate extra follicles, typically resulting in 5 to 15 eggs. Some women produce few follicles due to decreased ovarian reserve, while others may produce more, especially PCOS patients

The essential step happens on Day 0 when the eggs are fertilized. Once the eggs are retrieved, there’s a critical window in which they must be fertilized. With traditional IVF, eggs are mixed with sperm, and fertilization occurs naturally within the culture medium. In all of our IVF cycles, we utilize Intracytoplasmic Sperm Injection (ICSI), a fertilization technique that involves injecting a single sperm into each egg using a fine glass needle. It is a necessary step when planning genetic testing on an embryo.

Day 1: Ensuring Fertilization

On Day 1, our dedicated team of embryologists thoroughly examines every egg collected the previous day to confirm fertilization. Normally fertilized eggs feature two distinct circles within, representing genetic material from both the egg and the sperm. We call these "2 PN eggs." 

It's important to note that while most fertilizations result in the formation of 2 PN eggs, abnormal fertilization can occur. Abnormal fertilization may involve irregularities such as polyspermy, incomplete fertilization, or asymmetric division, leading to embryos with atypical genetic characteristics. It is not uncommon for some embryos to deviate from the typical 2 PN pattern and can still be considered to be developing normally.

Day 2 and 3: The Cleavage Stage

The fertilized egg begins its transformation by dividing. By Day 2, the fertilized egg undergoes its first division, resulting in four cells. These cells, known as blastomeres, are the building blocks of the developing embryo. Embryologists closely examine the blastomeres checking, cell numbers, symmetry, and signs of fragmentation. The goal is to ensure the embryo is on track for healthy development.

By Day 3, the embryo now consists of 6-10 cells and takes on the characteristic appearance of an 8-cell embryo. At this point, embryologists evaluate the embryo to make sure it is developing normally; examining the number and symmetry of cells and assessing if there are any signs of fragmentation. Fragmentation is a common phenomenon where small pieces of cytoplasm break off from the blastomeres. Successful implantation potential of the embryo relies on two key factors: minimal fragmentation and consistent progression in stage-appropriate development.

Day 5 and 6: The Blastocyst Stage

By Day 5, the embryo evolves into a blastocyst of hundreds of cells arranged in a hollow ball. The outer rim, known as the trophectoderm, will eventually develop into the placenta, while the inner cell mass will become the fetus.

It is important to know that not all Day 3 embryos will progress to the blastocyst stage. Typically, around 50% of embryos reach this advanced stage.

Fresh or Frozen Embryo Transfer – Making the Right Choice

Here are some points to consider when deciding between fresh and frozen embryo transfer:

PGT-A Cycles

If you opt for Preimplantation Genetic Testing for Aneuploidy (PGT-A) to test your embryos, it's essential to choose a freeze-all cycle. PGT-A results become available approximately a week after the embryo biopsy, conducted on Day 5 or Day 6 of IVF.

Dominion's Approach

At Dominion Fertility, all IVF cycles are freeze-all cycles. IVF can result in an endometrium (uterine lining) that might be less than ideal due to the fluctuating estrogen levels during the process. This is especially evident when using a Lupron trigger. We prioritize our patients' success, offering innovative and flexible treatment options tailored to their unique needs.

At Dominion Fertility, we're dedicated to ensuring your IVF journey is not just successful but also as smooth and comfortable as possible. Our expert team and state-of-the-art lab set us apart, making your dream of starting a family a reality.

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