The Science Behind IVF: How Test Tube Babies Are Born

The term "test tube baby" might sound like something from a science fiction novel, but it's actually a beautiful example of medical science helping nature along. If you've ever wondered how IVF actually works—what happens in those laboratory dishes, how doctors help sperm and egg meet, and how an embryo develops outside the body—you're in the right place.

In vitro fertilization has transformed from an experimental procedure to a well-established medical treatment that has brought millions of babies into the world. The first IVF baby, Louise Brown, was born in 1978, and since then, the science behind IVF has advanced tremendously. According to the Centers for Disease Control and Prevention (CDC), over 8 million babies worldwide have been born through IVF and related technologies.

Understanding the science behind IVF isn't just fascinating—it empowers you to make informed decisions, ask better questions, and feel more confident throughout your fertility journey. This guide breaks down the complex biology and laboratory techniques that make IVF possible, explained in simple terms that anyone can understand.

What Does "In Vitro" Actually Mean?

The term "in vitro fertilization" comes from Latin. "In vitro" literally means "in glass," referring to the glass laboratory dishes where eggs and sperm are combined. This is different from "in vivo," which means "in the living body." So IVF is fertilization that happens outside the body, in a controlled laboratory environment, rather than inside the fallopian tube where natural conception occurs.

The phrase "test tube baby" is actually a bit misleading—no test tubes are involved in modern IVF. Embryologists use shallow culture dishes called petri dishes, which provide the perfect environment for eggs, sperm, and developing embryos. But the nickname stuck because it captures the essential idea: conception happening in a laboratory rather than inside the body.

The Biology of Natural Conception: Setting the Foundation

To understand how IVF works, it helps to know what happens during natural conception. Your body performs an intricate dance of hormones, cell division, and precise timing every month.

The Natural Cycle

Your menstrual cycle is controlled by hormones released from your brain and ovaries. FSH (follicle-stimulating hormone) from your pituitary gland signals your ovaries to start growing follicles—small fluid-filled sacs that each contain an immature egg. Usually, one follicle becomes dominant and continues growing while others stop developing. This dominant follicle produces estrogen, which thickens your uterine lining in preparation for possible pregnancy.

When the follicle reaches the right size and estrogen levels peak, your pituitary gland releases a surge of LH (luteinizing hormone), which triggers ovulation. The mature egg bursts out of the follicle and is swept into the fallopian tube by finger-like projections called fimbriae.

If intercourse happens around this time, sperm travel through the cervix, through the uterus, and into the fallopian tubes. Only a few hundred of the millions of sperm actually reach the egg. One sperm penetrates the egg's protective outer layer, their genetic material combines, and fertilization occurs.

The newly fertilized egg (now called a zygote) begins dividing as it travels down the fallopian tube toward the uterus over about 5-6 days. By the time it reaches the uterus, it has developed into a blastocyst—a ball of about 100-200 cells with an inner cell mass (which becomes the baby) and an outer layer (which becomes the placenta). The blastocyst then implants into the uterine lining, and pregnancy begins.

Where Things Can Go Wrong

This complex process has many potential failure points. Ovulation might not occur regularly due to hormonal imbalances like PCOS. Fallopian tubes might be blocked from endometriosis, infections, or previous surgery, preventing sperm from reaching the egg. Sperm might be too few in number, move too slowly, or have abnormal shapes that prevent fertilization. The uterine environment might not be optimal for implantation due to fibroids, polyps, or thin lining. Egg quality might be compromised by age or other factors, leading to chromosomal abnormalities.

IVF was developed to overcome these obstacles by taking the critical steps of fertilization and early development into a controlled laboratory setting.

Step-by-Step: The Science of IVF

Step 1: Ovarian Stimulation – Creating Multiple Eggs

In a natural cycle, your body typically releases just one egg per month. For IVF to be most effective, doctors need to retrieve multiple eggs to maximize the chances of successful fertilization and embryo development.

The Hormone Protocol: You'll receive daily injections of synthetic hormones, primarily FSH and sometimes LH, for 10-14 days. These medications signal your ovaries to develop multiple follicles simultaneously instead of just one. According to the American Society for Reproductive Medicine (ASRM), this controlled ovarian stimulation is one of the most critical factors in IVF success.

Different protocols exist depending on your specific situation. Antagonist protocols use medications like Ganirelix or Cetrotide to prevent premature ovulation. Agonist protocols use medications like Lupron to first suppress your natural cycle before stimulation begins. Mini-IVF or natural cycle IVF uses lower medication doses or no stimulation, though these approaches typically retrieve fewer eggs.

Monitoring Your Response: Throughout stimulation, you'll have frequent monitoring appointments—typically every 2-3 days. Blood tests measure estrogen levels, which indicate how follicles are growing. Transvaginal ultrasounds measure follicle size and count. Doctors look for follicles reaching 18-20mm in diameter, which suggests eggs inside are mature.

Your doctor adjusts medication dosages based on how your body responds. Some women are "high responders" who develop many follicles quickly and need dose reductions to prevent ovarian hyperstimulation. Others are "slow responders" who need higher doses or extended stimulation periods.

The Trigger Shot: When enough follicles reach optimal size, you'll receive a "trigger shot"—an injection of hCG (human chorionic gonadotropin) or sometimes Lupron. This mimics the natural LH surge that causes final egg maturation. The trigger must be given exactly 36 hours before egg retrieval for optimal timing. Research published by the National Institutes of Health (NIH) shows that precise trigger timing significantly impacts egg maturity rates.

Step 2: Egg Retrieval – Harvesting Your Eggs

Egg retrieval is a minor surgical procedure performed in the fertility clinic's procedure room. You'll receive conscious sedation through an IV, which keeps you comfortable and relaxed but breathing on your own.

The Procedure: Your doctor uses a transvaginal ultrasound probe to visualize your ovaries. Attached to the probe is a thin needle that passes through the vaginal wall into each ovarian follicle. Gentle suction draws out the follicular fluid containing the egg. Each follicle is aspirated individually, and the fluid is immediately passed to the embryology laboratory.

The entire procedure typically takes 20-30 minutes, depending on how many follicles you have. You'll rest in recovery for 1-2 hours before going home the same day. Most women experience mild cramping and bloating afterward but can return to normal activities within a day or two.

In the Laboratory: As each follicle is aspirated, embryologists examine the fluid under a microscope to locate the eggs. Eggs are tiny—about the size of a grain of sand—and surrounded by cumulus cells that nourished them while growing in the follicle. The embryologist identifies and isolates each egg, then places them in culture dishes with special media that mimics the natural environment of the fallopian tube.

Not every follicle contains an egg, and not every egg retrieved will be mature. Mature eggs (called MII oocytes) have completed their first division and are ready for fertilization. Immature eggs might still be able to mature in the laboratory but have lower fertilization rates.

Step 3: Sperm Collection and Preparation

On the same day as egg retrieval, sperm must be collected and prepared for fertilization.

Collection Methods: The male partner typically provides a fresh semen sample through masturbation in a private room at the clinic. If this isn't possible due to stress or other factors, samples can sometimes be collected at home and brought to the clinic within an hour. For men with very low sperm counts or who've had vasectomies, surgical sperm extraction procedures like TESA (testicular sperm aspiration) or PESA (percutaneous epididymal sperm aspiration) can retrieve sperm directly from the testicles or epididymis. Frozen sperm from previous collections or from sperm donors can also be used.

Sperm Washing and Selection: Raw semen contains more than just sperm—it includes seminal fluid, dead sperm cells, white blood cells, and other debris. The embryology team processes the sample to isolate the healthiest, most motile sperm.

The sample is mixed with special washing media and centrifuged (spun at high speed) to separate sperm from seminal fluid. The sperm pellet is then resuspended in fresh media. This process is repeated several times. Advanced techniques like density gradient centrifugation separate sperm by quality—the healthiest sperm swim to a specific layer where they can be collected. Swim-up techniques allow the most motile sperm to swim away from debris into clean media.

After processing, embryologists count the sperm and assess their motility (movement) and morphology (shape). This information helps determine whether standard IVF or ICSI is most appropriate.

Step 4: Fertilization – Bringing Egg and Sperm Together

This is where the magic happens—the moment when genetic material from egg and sperm combine to create a unique embryo.

Conventional IVF: Each mature egg is placed in a small dish containing culture medium. Approximately 50,000-100,000 processed sperm are added to the dish around each egg. The eggs and sperm incubate together for several hours, during which sperm naturally swim to and attempt to penetrate the egg.

For fertilization to succeed, a sperm must first break through the cumulus cells surrounding the egg, then bind to and penetrate the zona pellucida (the egg's protective outer shell), and finally fuse with the egg membrane and release its genetic material inside. When a sperm successfully enters, the egg immediately changes to prevent additional sperm from entering. The egg completes its final division, and the genetic material from sperm and egg (each containing 23 chromosomes) combine to form a complete set of 46 chromosomes.

ICSI (Intracytoplasmic Sperm Injection): When sperm quality is poor or previous IVF attempts had fertilization failure, ICSI is used. This technique was developed in the early 1990s and revolutionized treatment for male factor infertility.

Under a powerful microscope, an embryologist uses micromanipulation tools to select individual sperm. A single sperm is drawn into a tiny glass needle (thinner than a human hair). The egg is held steady with a holding pipette while the injection needle carefully penetrates the zona pellucida and egg membrane, depositing the sperm directly into the egg cytoplasm.

According to National Institute for Health and Care Excellence (NICE) guidelines, ICSI is recommended when severe male factor infertility exists, previous IVF cycles had low or no fertilization, using frozen sperm with low counts, using surgically retrieved sperm, or when preimplantation genetic testing is planned.

ICSI fertilization rates typically range from 70-80%, slightly higher than conventional IVF's 60-70% for normal sperm parameters, because it bypasses the sperm's need to penetrate the egg naturally.

Checking for Fertilization: The morning after egg retrieval (about 16-18 hours after combining eggs and sperm), embryologists check each egg for signs of fertilization. Successfully fertilized eggs show two pronuclei—one containing genetic material from the egg and one from the sperm—before they merge together. Eggs showing this are confirmed fertilized and will continue to develop. Unfertilized eggs or those showing abnormal fertilization patterns are discarded.

Step 5: Embryo Development – Watching Life Begin

Once fertilization is confirmed, embryos are placed in specialized incubators that precisely control temperature, humidity, oxygen levels, and pH to mimic conditions inside the body. Modern embryology labs use time-lapse imaging systems that photograph embryos every 10-20 minutes, allowing embryologists to monitor development without removing embryos from the incubator.

Day 1 (Fertilization Day): The fertilized egg is called a zygote. The two pronuclei are visible, containing genetic material from both parents.

Day 2: The zygote divides into 2-4 cells. Each cell is called a blastomere. At this stage, embryos should show even cell division and minimal fragmentation (cellular debris).

Day 3: Embryos typically contain 6-8 cells. This is when the embryo's own genetic blueprint starts directing development (before this, the egg's stored resources guide the process). Some clinics perform embryo transfer on day 3, though day 5-6 transfers are increasingly common.

Day 4: Embryos enter the morula stage, forming a compact ball of 16-32 cells. The cells begin to compact tightly together.

Day 5-6: Embryos reach the blastocyst stage, containing about 100-200 cells organized into two distinct parts—the inner cell mass (which will become the fetus) and the trophectoderm (which will become the placenta). The blastocyst also develops a fluid-filled cavity called the blastocoel.

Not all fertilized eggs make it to blastocyst stage. Typical progression rates are approximately 80-90% of fertilized eggs develop to day 3, and 40-60% of day 3 embryos develop to quality blastocysts. This natural selection process helps identify the strongest embryos with the best developmental potential.

Embryo Grading: Embryologists assess embryo quality at various stages using standardized grading systems. For blastocysts, grading considers the expansion of the blastocoel (rated 1-6, with higher numbers indicating more expanded), inner cell mass quality (graded A, B, or C based on cell number and compactness), and trophectoderm quality (also graded A, B, or C based on cell number and cohesiveness).

A grade 4AA blastocyst, for example, would be an expanded blastocyst with excellent inner cell mass and trophectoderm. However, even "lower grade" embryos can result in healthy pregnancies—grading helps prioritize which embryos to transfer first but isn't an absolute predictor of success.

Step 6: Embryo Transfer – Returning Embryos to the Uterus

Embryo transfer is the final step where embryos are placed into your uterus to implant and grow.

Fresh vs. Frozen Transfer: Fresh transfers occur 3-6 days after egg retrieval in the same cycle. Your uterine lining has been preparing naturally during ovarian stimulation. Frozen transfers happen in a later cycle after embryos have been cryopreserved. Your uterine lining is prepared with medications without the hormonal elevation from ovarian stimulation. Research published by the NIH suggests frozen transfers may actually have slightly higher success rates in some situations because the uterine environment is more receptive.

The Transfer Procedure: You'll have a full bladder during transfer, which helps position the uterus optimally. Using an abdominal ultrasound to visualize the uterus, your doctor gently inserts a speculum and cleans the cervix. A thin, flexible catheter containing the selected embryo(s) in a tiny amount of fluid is carefully threaded through the cervix into the uterus. The embryologist confirms the embryo has been expelled by checking the catheter under a microscope.

The entire procedure takes about 5-10 minutes and feels similar to a pap smear. No anesthesia is needed, though some doctors prescribe a mild sedative if you're very anxious. You'll rest briefly afterward, then can resume normal activities. There's no evidence that bed rest after transfer improves outcomes—in fact, normal activity is encouraged.

How Many Embryos to Transfer: Modern IVF practice strongly favors single embryo transfer (SET) to avoid multiple pregnancy risks. According to American College of Obstetricians and Gynecologists (ACOG) guidelines, transferring one high-quality blastocyst in women under 38 provides excellent pregnancy rates while virtually eliminating twin and triplet risks.

Two embryos might be considered for women over 40, those with previous failed transfers, or when only fair-quality embryos are available. Transferring three or more embryos is rarely recommended due to serious multiple pregnancy complications.

Step 7: The Two-Week Wait and Pregnancy Testing

After transfer, the embryo must implant into your uterine lining. This typically happens 1-5 days after a day 5 blastocyst transfer (or 6-10 days after ovulation in natural terms).

Luteal Phase Support: You'll take progesterone supplements—via injections, vaginal suppositories, or pills—to support the uterine lining and help the embryo implant. This mimics the natural progesterone your corpus luteum (the leftover follicle structure) would produce. Even though the corpus luteum produces some progesterone, supplementation ensures optimal levels.

The Waiting Period: About 10-14 days after transfer, you'll have a blood test measuring beta hCG (the pregnancy hormone). This is more accurate than home pregnancy tests and provides numerical values that indicate pregnancy progression. A positive result means the embryo implanted successfully. You'll have repeat blood tests 2-3 days apart to confirm hCG levels are rising appropriately.

About 2-3 weeks after a positive beta test (around 6-7 weeks from your last period), you'll have an ultrasound to confirm a gestational sac and fetal heartbeat—this is called a clinical pregnancy.

Advanced IVF Technologies

Preimplantation Genetic Testing (PGT)

PGT allows analysis of embryo genetics before transfer, helping identify the healthiest embryos.

The Biopsy Process: On day 5 or 6, a few cells (typically 5-10) are carefully removed from the trophectoderm (outer layer) of the blastocyst using a laser or mechanical technique. This doesn't harm the embryo since the cells removed would become placenta, not the baby. The biopsied cells are sent to a genetics laboratory while embryos are frozen.

PGT-A (Aneuploidy Screening): This test checks if embryos have the correct number of chromosomes (46 total—23 pairs). Embryos with too many or too few chromosomes (aneuploid embryos) usually won't implant, or will result in miscarriage, or in some cases conditions like Down syndrome. PGT-A is particularly valuable for women over 35, those with recurrent miscarriage, or previous failed transfers. The World Health Organization (WHO) recognizes PGT as an important tool for improving IVF outcomes in appropriate situations.

PGT-M (Monogenic Disorder Testing): This identifies embryos affected by specific genetic diseases like cystic fibrosis, sickle cell disease, or Huntington's disease when parents are known carriers.

PGT-SR (Structural Rearrangement Testing): This is used when a parent has chromosomal rearrangements like translocations or inversions that could cause miscarriage or birth defects.

Results typically take 1-2 weeks. Embryos identified as chromosomally normal can be transferred in a subsequent frozen embryo transfer cycle.

Embryo Freezing (Cryopreservation)

Modern embryo freezing uses vitrification—an ultra-rapid freezing technique that prevents ice crystal formation that could damage embryos.

The Vitrification Process: Embryos are placed in solutions containing cryoprotectants (antifreeze-like substances) that replace water in the cells. They're then plunged into liquid nitrogen at -196°C (approximately -321°F), freezing so rapidly that ice crystals can't form. The entire process takes just minutes. Frozen embryos are stored in liquid nitrogen tanks where they remain viable indefinitely—embryos frozen for 10-20 years have resulted in healthy babies.

Thawing and Transfer: When you're ready to use frozen embryos, they're rapidly warmed and the cryoprotectant is removed. Modern vitrification has survival rates exceeding 95%—meaning nearly all frozen embryos survive the freeze-thaw process. Pregnancy rates with frozen embryos are comparable to or sometimes better than fresh transfers.

Assisted Hatching

The embryo is surrounded by a protective shell called the zona pellucida. For implantation, the blastocyst must "hatch" out of this shell. Some embryos have difficulty hatching, particularly those with thickened zona (common in older women) or those that have been frozen.

Assisted hatching uses a laser or chemical solution to create a small opening in the zona pellucida before transfer, helping the embryo hatch more easily. This technique may improve implantation rates in specific situations, though it's not beneficial for all patients.

Time-Lapse Imaging

Traditional embryo assessment requires removing embryos from the incubator for microscopic examination. Time-lapse incubators contain built-in cameras that photograph embryos every few minutes without disturbance. This provides continuous monitoring of embryo development, revealing information about division timing and patterns that might predict which embryos have the best implantation potential.

The Embryology Laboratory: Where Science Happens

Creating the Perfect Environment

Embryology laboratories must maintain precise conditions that mimic the body's natural environment. Temperature is controlled to exactly 37°C (98.6°F). Humidity is maintained at very high levels to prevent culture media evaporation. Gas mixture includes reduced oxygen (5-6% rather than the 20% in room air) similar to conditions in the fallopian tube. pH is carefully regulated in culture media. Air quality is strictly controlled with HEPA filters and positive pressure to prevent contamination.

Even tiny variations in these factors can affect embryo development, so laboratories monitor conditions continuously.

Culture Media: The Embryo's Food

Culture media are specialized liquids containing nutrients, amino acids, vitamins, and other substances embryos need for development. Different media formulations support different developmental stages—one for early cleavage (day 1-3) and another for blastocyst development (day 4-6).

Media composition is based on decades of research into what embryos need at each stage. Companies that produce culture media spend years perfecting formulations and testing them extensively before use in human IVF.

The Embryologist's Role

Embryologists are the unsung heroes of IVF. These highly trained specialists handle eggs, sperm, and embryos with incredible skill and precision. Their work requires advanced degrees (typically master's or doctoral level), specialized training in reproductive biology and laboratory techniques, steady hands and excellent microscope skills, attention to detail and quality control, and the ability to work under pressure while maintaining perfect accuracy.

Every step—from identifying eggs in follicular fluid to performing ICSI to grading embryos—requires expertise that comes from years of training and experience.

Understanding Success Rates: What the Science Tells Us

IVF success depends on numerous factors, with maternal age being the most significant predictor. Women under 35 typically have live birth rates of 50-55% per embryo transfer. Women 35-37 have about 40-45% success rates. Women 38-40 have approximately 30-35% success rates. Women 41-42 have around 20-25% success rates. Women over 42 have success rates declining to 10-15% or lower.

These numbers reflect per-transfer rates. Cumulative success rates across multiple embryos from a single retrieval are significantly higher.

Other factors affecting success include embryo quality (blastocysts and genetically tested embryos have higher success), number of eggs retrieved (more eggs provide more opportunities), sperm quality (though ICSI can overcome most male factor issues), uterine health (optimal lining thickness and no structural abnormalities), lifestyle factors (healthy weight, no smoking, limited alcohol), and clinic expertise (experienced clinics with modern laboratories typically have better outcomes).

Common Questions About IVF Science

Does ICSI increase the risk of birth defects?

Extensive research shows ICSI babies have similar rates of birth defects to babies conceived through conventional IVF or natural conception. Early concerns about ICSI have not been confirmed in long-term studies. The slightly elevated rates sometimes reported are primarily related to the underlying male infertility factors rather than the ICSI procedure itself.

Can embryos be damaged during freezing?

Modern vitrification has made embryo freezing extremely safe with survival rates exceeding 95%. Babies born from frozen embryos have similar health outcomes to those from fresh transfers. In fact, some research suggests frozen embryo transfers may have slightly lower preterm birth rates.

How long can embryos remain frozen?

Embryos can remain cryopreserved indefinitely. Successful pregnancies have resulted from embryos frozen for 10, 15, even 20+ years. The freezing process essentially stops all biological activity, so time in storage doesn't degrade embryo quality.

Why don't all fertilized eggs become blastocysts?

Embryo development is a natural selection process. Chromosomal abnormalities, cell division errors, or developmental problems cause many embryos to stop developing. This happens in natural conception too—many fertilized eggs never implant. The difference is that in IVF, we can observe this process. The attrition from fertilized egg to blastocyst is actually helpful, as embryos that wouldn't result in successful pregnancy are identified before transfer.

Is IVF scientifically safe for babies long-term?

Decades of follow-up studies on IVF children show reassuring results. IVF children have similar rates of developmental milestones, academic performance, social adjustment, and adult health compared to naturally conceived children. The oldest IVF babies are now in their 40s and have their own healthy children, demonstrating IVF's long-term safety.

How does the laboratory know which embryo is mine?

Embryology labs have strict identification protocols. Every dish, tube, and culture plate containing your eggs, sperm, or embryos is labeled with your unique identification information. Two embryologists independently verify identity at every critical step (egg retrieval, fertilization, ICSI, embryo transfer). Some labs use electronic witnessing systems with barcode scanning to prevent any possibility of mix-up.

What happens to embryos that aren't transferred?

High-quality embryos are typically frozen for future use. Lower-quality embryos that developed but weren't suitable for transfer or freezing are discarded. You decide what happens to frozen embryos—options include using them for future pregnancies, donating them to another couple, donating them for research, or having them discarded.

The Future of IVF Science

IVF technology continues advancing rapidly. Artificial intelligence now helps analyze embryo images to predict which ones have the best implantation potential. Non-invasive genetic testing examines culture media or cells naturally shed by embryos rather than requiring biopsy. Improvements in culture media and incubator technology continue optimizing embryo development. Research into uterine receptivity helps time transfers more precisely. Mitochondrial replacement therapy may help women with egg quality issues related to mitochondrial function.

These advances promise to make IVF even more effective and accessible in coming years.

Your Journey Through IVF Science

Understanding the science behind IVF transforms it from a mysterious "medical procedure" into a logical series of steps that assist your body's natural processes. Every injection, every monitoring appointment, every laboratory technique serves a specific purpose in creating the optimal conditions for new life to begin.

The science of IVF represents decades of research, technological innovation, and clinical experience. The embryologists working with your cells have spent years perfecting their skills. The medications you receive are precisely calibrated to your body's needs. The laboratory environment is meticulously controlled to support embryo development.

While the science is complex, the goal is beautifully simple: helping you have the healthy baby you've been dreaming of.

At Urvara Fertility Centre, we combine cutting-edge IVF science with compassionate, personalized care. Our state-of-the-art embryology laboratory features the latest technology and equipment. Our experienced embryologists bring decades of combined expertise. Our fertility specialists stay current with the latest research and techniques. Most importantly, we explain every step of the science in terms you can understand, so you feel informed and confident throughout your journey.

The science behind IVF is remarkable, but what's even more remarkable is what it makes possible—your future family. We're honored to use this incredible science to help make your dreams of parenthood a reality.

Medical Disclaimer

This article provides general educational information about IVF science and procedures. It should not replace personalized medical advice from qualified healthcare providers. IVF protocols, techniques, and recommendations vary based on individual circumstances. Always consult with board-certified reproductive endocrinologists and embryologists for guidance specific to your situation.

References

Centers for Disease Control and Prevention (CDC). Assisted Reproductive Technology (ART) Success Rates and Data. Available at: https://www.cdc.gov/art/reports/index.html
American Society for Reproductive Medicine (ASRM). In Vitro Fertilization: IVF Science and Technology. Available at: https://www.asrm.org/topics/topics-index/in-vitro-fertilization-ivf/
National Institutes of Health (NIH). IVF Procedures and Embryo Development Research. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5882341/
National Institutes of Health (NIH). Fresh versus Frozen Embryo Transfer Outcomes. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6119597/
National Institute for Health and Care Excellence (NICE). Fertility Treatment Guidelines and Evidence. Available at: https://www.nice.org.uk/guidance/cg156
American College of Obstetricians and Gynecologists (ACOG). Assisted Reproductive Technology Safety and Outcomes. Available at: https://www.acog.org/
World Health Organization (WHO). Infertility and Assisted Reproductive Technologies. Available at: https://www.who.int/news-room/fact-sheets/detail/infertility
European Society of Human Reproduction and Embryology (ESHRE). IVF Laboratory Guidelines and Best Practices. Available at: https://www.eshre.eu/