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Timeline with images of embryo development in IVF

fully hatched day 6 blastocyst

Many fertility patients are curious about what exactly happens in the embryology lab, from the time their eggs are retrieved to the time they are transferred. When people have answers to their questions about the details of embryo development, IVF can become a less mysterious process for them.

With that in mind, here is a day-by-day timeline of what happens in the embryology lab in IVF.

embryo development IVF 1

Day 0: Retrieval Day

This is known as your retrieval day. On day 0, the eggs are retrieved from the follicles that have resulted from your ovarian stimulation. At this time the retrieved eggs are counted and assessed for maturity/quality.

The sperm is also prepped and readied for insemination or ICSI of the retrieved eggs. Approximately 4-6 hours after your retrieval, the eggs will be inseminated or injected with sperm (ICSI). This image shows a mature egg (metaphase II) at the moment of ICSI.

Day 1: Looking for Fertilization

normally fertilized human embryo

The eggs are evaluated for fertilization, the fusion or combining of the egg and sperm, approximately 16-18 hours after insemination. Normal fertilization is the presence of two pronuclei, one from the egg and one from the sperm.

abnormally fertilized human embryo If there are too few or too many pronuclei, that embryo is considered abnormally fertilized. All normally fertilized embryos are put into a special media that mimics the tubal fluid found in the human body.

The gold-toned image (above right) shows a normally fertilized embryo. The black-and-white one (above left) shows an abnormally fertilized embryo.

Day 2: Checking for Good Cell Division

day 2 embryo developmentThe embryos are briefly looked at to assess cell division. Most embryos will have between 2-4 cells on day 2. The image to the right shows a 2-day-old, 4-celled embryo.

If the embryo has not divided by this time, that embryo is considered non-viable.

At this time, embryology will decide if a day 3 or a day 5 transfer will occur. This is typically based on the quality of cell division of the embryos, and the number of embryos available.

Day 3: PGD Biopsy and Possible Transfer Day

day 3 embryo development timeline

Day 3: Embryos at this stage usually have 6-8 cells. If you are having your embryo transfer, assisted zona hatching, making a breach in the shell of the embryo might be performed.

This is also the day embryo biopsy for PGD (pre-implantation genetic diagnosis) may occur. If you are not having your transfer, the embryos are placed into new media that mimics the uterine fluid of the human body.

Day 4: Compacting

compacted day 4 morulaYour embryos continue to grow and develop into a compact ball of cells, about 16 in all, known as a morula. If compaction does not start to occur on this day, blastocyst formation rates are decreased. This image shows a compacted day 4 morula.

Day 5: The Blastocyst Forms

day 5 blastocyst implantation timeline ivfOn day 5, the embryo develops into a blastocyst. At this stage, it is usually possible to grade the inner cell mass (ICM), the fetal component, and the trophectoderm cells (TE), the placental component, of the embryo. Embryo transfers are often done on day 5, as well as cryopreservation of any fully expanded blastocysts. Any remaining viable embryos that are not fully developed are cultured on for possible freezing on day 6.

Day 6: Last Day to Transfer or Freeze

transfer frozen embryosDay 6: Embryos on day 6 must be either transferred, if transfer was not done on day 5, or frozen.

Any non-viable embryos are discarded. Day 6 is the last day that an embryo can remain in the lab without being transferred or cryopreserved.

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Infertility Embryology

Liza Roscetti Meyer

Liza Roscetti Meyer

Liza has been an embryologist at InVia Fertility Specialists since 2002. She completed her studies, first in animal science at Southern Illinois University, followed by clinical embryology/reproductive genetics at Eastern Virginia Medical School. Her interests include reproductive genetics, fertility preservation, and mitochondrial function in the human oocyte. She loves being a part of helping others achieve and experience the joy of becoming a parent. Seeing the end result .your baby.makes all the hours in the lab worth it!


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