PGT Genetic Testing in IVF: How It Works

Preimplantation Genetic Testing (PGT) is a group of laboratory techniques performed on IVF embryos before transfer to the uterus. By analyzing a small biopsy of cells from the blastocyst, PGT can identify chromosomal abnormalities, single-gene disorders, and structural chromosomal rearrangements - allowing the fertility team to select the embryo with the highest potential for a healthy pregnancy.

Types of PGT

PGT-A (Aneuploidy Screening)

PGT-A tests whether each embryo has the correct number of chromosomes (46 in humans - 23 pairs). Embryos with too many or too few chromosomes (aneuploid) are the primary cause of IVF implantation failure, miscarriage, and chromosomal conditions. The rate of aneuploidy increases dramatically with maternal age:

• Age 30: ~30% of embryos are aneuploid
• Age 35: ~40% aneuploid
• Age 38: ~60% aneuploid
• Age 40: ~70-80% aneuploid
• Age 43+: ~90% aneuploid

By identifying and selecting only euploid (chromosomally normal) embryos, PGT-A dramatically reduces the two most common adverse outcomes: failed implantation and miscarriage.

PGT-M (Monogenic/Single-Gene Disorders)

PGT-M tests for specific inherited genetic diseases when one or both parents are known carriers. It requires custom probe design for each family - the testing protocol is tailored to the specific mutation being screened. Common indications:

• Cystic fibrosis (CFTR mutations)
• Sickle cell disease
• Thalassemia
• Huntington's disease
• BRCA1/BRCA2 (hereditary breast and ovarian cancer)
• Spinal muscular atrophy (SMA)
• Fragile X syndrome

PGT-SR (Structural Rearrangements)

For patients who carry balanced chromosomal translocations or inversions. These structural rearrangements increase the risk of producing embryos with unbalanced chromosomal content - leading to recurrent miscarriage or offspring with chromosomal abnormalities.

The PGT Process

1. Standard IVF cycle: Ovarian stimulation, egg retrieval, fertilization, and embryo culture proceed as in a regular IVF cycle.
2. Blastocyst biopsy (Day 5-6): When the embryo reaches the blastocyst stage, an embryologist removes 5-8 cells from the trophectoderm (the outer cell layer that will become the placenta). The inner cell mass (which becomes the baby) is not touched.
3. Vitrification: The biopsied embryo is immediately vitrified (frozen) while awaiting test results.
4. Genetic analysis: The biopsy sample is analyzed using Next-Generation Sequencing (NGS) - the most advanced and accurate platform currently available. Results take 1-2 weeks.
5. Results counseling: The fertility team reviews results with you, categorizing each embryo as euploid, aneuploid, or mosaic.
6. Frozen embryo transfer (FET): A frozen embryo transfer is scheduled for the best euploid embryo in a subsequent cycle.

The Mosaic Question

Mosaic embryos contain a mixture of normal and abnormal cells. They represent approximately 10-20% of tested embryos and create a clinical dilemma: should they be transferred?

Current evidence: low-level mosaicism (less than 40% abnormal cells) can result in healthy pregnancies, as the embryo may self-correct during development. High-level mosaicism carries higher risk. PGDIS (Preimplantation Genetic Diagnosis International Society) guidelines recommend discussing mosaic embryo transfer as an option when no euploid embryos are available - with appropriate genetic counseling.

Who Benefits Most from PGT?

• Women over 35: Higher baseline aneuploidy rate means PGT-A provides the greatest absolute benefit.
• Recurrent pregnancy loss: 2+ miscarriages - up to 60% of early miscarriages are caused by embryonic aneuploidy.
• Repeated implantation failure: 3+ failed transfers - selecting euploid embryos may solve the issue.
• Known genetic carriers: PGT-M is the only way to prevent transmission of known single-gene disorders without sacrificing the ability to have genetically related children.
• Single embryo transfer optimization: When you want to transfer one embryo for the best chance - PGT-A identifies which one.

At Wholecares partner IVF centers, PGT-A is performed using certified NGS platforms with results turnaround of 7-10 working days. PGT-M custom probe design is available for 200+ known genetic conditions. All testing includes pre- and post-test genetic counseling as standard.