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Inside the IVF Laboratory
Embryology is the heart of the fertility journey. Behind every successful IVF cycle is a team of skilled embryologists working in a carefully controlled laboratory, using advanced techniques to nurture the earliest stages of human life. Here’s an inside look at what happens in the lab, from sperm collection and egg retrieval to embryo transfer.
Semen Collection and Sperm Processing
The journey begins with collecting a semen sample from the male partner, either on-site at the clinic or from a frozen sample stored ahead of time. Usually, the male partner will produce a fresh semen sample via masturbation in our collection room. However, in some cases, surgical sperm retrieval (PESA, TESA, MESA, or micro-TESE) may be required. A complete semen analysis, ordered by your doctor well in advance of the egg retrieval procedure, will determine the appropriate semen collection method to be used on the day of egg retrieval.
Once in the lab, the sperm is carefully washed from the semen and processed to isolate the healthiest, most motile sperm. Techniques such as density gradient centrifugation or swim-up methods are used to select the best candidates for fertilization. More recent advancements of sperm processing include the use of microfluidic devices that allow highly motile and morphologically normal sperm to self-select by swimming through specially engineered microchannels and micropores, without the need for centrifugation processing, which may help prevent sperm DNA damage.
Egg Collection (Oocyte Retrieval)
After ovarian stimulation, eggs are aspirated from ovarian follicles using a minimally invasive procedure under ultrasound guidance. Once collected, the follicular fluid is brought to the embryologist, who uses a microscope to carefully search for eggs contained in this fluid. Each egg is then carefully washed, placed in special culture dishes containing culture medium that mimics the natural environment of the female reproductive tract, and placed in incubators to await the addition of sperm. Note that the male partner will be scheduled to produce his fresh semen sample on the same day as the egg retrieval procedure.
Insemination (Standard IVF)
For standard IVF, sperm and eggs are placed together in a petri dish to allow the sperm to penetrate the egg on its own. Standard IVF is an excellent technique to use if the sperm are plentiful, have good morphology (shape, or general appearance) and are actively swimming. Eggs have a built-in mechanism that only allows one sperm to penetrate the outer covering of the egg. The number of sperm added to each egg is carefully controlled, and the dish is placed in an incubator for fertilization to occur overnight. Early the next morning, each egg is evaluated to determine if fertilization has occurred.
Intracytoplasmic Sperm Injection (ICSI)
In cases of male factor infertility, previous fertilization failure, or if frozen sperm is being used, ICSI insemination is highly recommended. A single sperm cell is directly injected into the cytoplasm of each mature egg using a fine glass needle. This highly delicate technique requires expert precision and dramatically increases fertilization chances. Once injected, eggs are placed back into the incubator to await fertilization assessment the following day.
Embryo Culture and Incubation
Once fertilization occurs, the developing embryos are cultured in incubators that closely replicate the environment of the uterus. Embryos are monitored and graded over the next seven days to evaluate development and quality. Only the healthiest embryos are selected for transfer or freezing.
When placed into the appropriate culture environment, embryos develop from 1-cell fertilized zygotes (Day 1) into blastocyst-stage embryos (Day 5 and Day 6). The following stages of development are:
- 2 PN (two pronuclei) on Day 1
- 2-cell to 4-cell on Day 2
- 8-cell on Day 3
- Morula on Day 4
- Early Blastocyst on Day 5
- Expanding Blastocyst on Day 5 or Day 6
- Hatching Blastocyst on Day 5 or Day 6
- Hatched Blastocyst on Day 5 or Day 6
Time-Lapse Incubators
Time-lapse incubators are one of the most exciting advancements in modern IVF technology. Unlike traditional incubators, which require embryos to be briefly removed for observation, time-lapse incubators contain built-in cameras that continuously take microscopic images of each developing embryo. These images are compiled into a video, allowing embryologists to closely monitor the entire development process without disturbing the embryo’s environment.
One of the biggest advantages of time-lapse incubators over conventional incubators is that they help maintain optimal, uninterrupted conditions for embryo development. Using today’s generation of single-step culture media combined with time-lapse incubation, the embryo can remain undisturbed for the entire duration of culture up until the time for embryo transfer, biopsy or cryopreservation. With traditional incubators, embryos must be removed from the incubator to check for fertilization and cell division under a microscope, which exposes them briefly to changes in temperature, pH, light, and air atmosphere. By reducing these stressors, time-lapse incubators may improve IVF outcomes. Time-lapse systems eliminate the need to remove embryos from the carefully controlled incubator environment, keeping the embryos in a safe, stable, womb-like environment 24/7.
Another major benefit is improved embryo selection. Time-lapse imaging provides detailed information on how each embryo is developing: not just how it looks at a single point in time, but how it grows and divides over hours and days. Embryologists can identify subtle patterns in timing and behavior that are linked to higher implantation potential, helping them select the embryo with the best chance of success. Finally, time-lapse incubators offer an added level of documentation and transparency. Patients may even be shown a short video of their embryo’s early development, making the process more tangible and personal. Overall, time-lapse incubators combine technology and efficiency which may improve IVF outcomes by reducing stress on the embryos.
Embryo Transfer
Embryo transfer is a simple, painless procedure performed in the clinic, similar to an IUI procedure. The chosen embryo is loaded into a soft catheter and carefully placed into the uterus under ultrasound guidance. No sedation is needed, and patients can usually resume normal activities shortly after. Note that single-embryo transfer has become the standard of care to avoid twinning. Advancements in embryo culture systems, media composition, and incubator design have all led to a high percentage of embryos progressing to the blastocyst stage (the ideal stage to transfer embryos to the uterus). In fact, transferring a single, blastocyst stage embryo leads to similar pregnancy rates compared to transferring two or more Day 3 stage embryos without the risk of twins or triplets.
Embryo Biopsy (for PGT-A, PGT-M or PGT-SR)
For patients choosing preimplantation genetic testing (PGT), a few cells are removed (biopsied) from each blastocyst stage embryo (usually on Day 5 or Day 6 of development) to check for genetic or chromosomal issues before the embryo is transferred to the uterus. The goal is to select embryos free from chromosomal abnormalities or inherited conditions.
- older patients
- recurrent IVF failures
- genetic disease carriers
Meanwhile, the removed cells are sent to a specialized genetics lab to check for:
- chromosomal anomalies (like Down syndrome): this is called PGT-A (or aneuploidy testing)
- inherited conditions (like cystic fibrosis): this is called PGT-M (or monogenic testing)
Once the test results come back (usually within 2 weeks), a chromosomally normal embryo can be transferred in a future frozen embryo transfer (FET) cycle.
Embryo Cryopreservation (Vitrification)
Embryos not transferred fresh can be frozen (cryopreserved) for future use using vitrification, which is a rapid freezing method that prevents the formation of ice crystals, which can damage cells. This technique ensures excellent survival rates after thawing. Vitrification has become the standard of care which replaced conventional (slow freeze) methods over a decade ago.
Frozen Embryo Transfer (FET)
Cryopreserved embryos can remain viable indefinitely while stored at cryogenic temperatures (-196 °C or -320 °F). On the scheduled morning of the frozen embryo transfer (FET) procedure, a single embryo is quickly warmed in special warming solution and prepared for uterine transfer later that same day. The FET is then performed exactly like a fresh embryo transfer.
Embryos that have been cryopreserved via vitrification can be thawed and transferred to the uterus and have similar or higher pregnancy rates compared to fresh embryo transfers. This high success rate is due to:
- he vitrification process itself which ensures excellent survival rates post-thawing
- frozen/thawed embryos are transferred into an unstimulated, “quiescent” uterus, unlike a fresh embryo transfer in which the uterus is still under the influence of residual exogenous hormones administered during the ovarian stimulation cycle
Egg Freezing (Oocyte Cryopreservation)
Similar to embryo cryopreservation, eggs can also be vitrified and stored for future use. This is an option for patients wishing to preserve fertility due to medical treatment or personal choice. At the appropriate time, frozen eggs can be thawed, inseminated via ICSI, and allowed to develop in culture. Frozen/thawed eggs can develop into useable blastocysts at rates comparable to using fresh eggs.
Equipment Monitoring & Emergency Generator
Every incubator, freezer, refrigerator, liquid nitrogen storage dewar and the lab environment itself is continuously monitored 24/7. Advanced sensor systems track incubator and embryo storage tank temperatures, gas concentrations and levels, humidity, VOC levels, and electrical power failure events to ensure optimal conditions. Alerts are triggered if anything drifts outside strict parameters, always ensuring the safest environment for eggs, sperm and embryos. Alarms are continuously monitored real-time by a third-party monitoring company that will notify laboratory staff by telephone, email and text messaging of any alerts.
An emergency diesel generator, capable of running the entire suite of laboratory equipment in the event of an electrical power outage, is maintained on-site and exercised weekly, serviced quarterly and tested biannually to ensure that we have a reliable source of power when needed.
Lab Security and Safety
The IVF lab is a high-security, restricted-access environment. Only authorized laboratory personnel have access to the IVF laboratory, which is secured by electromagnetic locks controlled by keypad access. Similarly, the medical gas tank room is secured by electromagnetic locks on access doors that can only be opened by authorized laboratory personnel.