Preimplantation Genetic Testing for Aneuploidies (PGT-A) is a laboratory procedure performed during an IVF cycle that allows embryos to be screened for chromosomal abnormalities before being transferred to the uterus. By identifying embryos with the correct number of chromosomes — a state known as euploid — PGT-A aims to improve IVF success rates, reduce the risk of miscarriage, and shorten the time to a successful pregnancy.
Chromosomal abnormalities (aneuploidies) are the most common cause of implantation failure and early miscarriage. PGT-A gives clinicians crucial information to select the embryo with the highest likelihood of developing into a healthy pregnancy.
"PGT-A adds a layer of certainty to embryo selection — helping us transfer the embryo most likely to succeed, first time."
How PGT-A Works
IVF to Blastocyst Stage
Embryos are cultured in the laboratory to the blastocyst stage (day 5 or 6), which is when the cells have differentiated sufficiently for biopsy to be performed safely.
Embryo Biopsy
A senior embryologist removes 3–8 cells from the trophectoderm (the outer layer that will form the placenta) of each blastocyst using a laser. The inner cell mass — which will become the baby — is left completely intact.
Vitrification
All biopsied embryos are immediately vitrified (snap-frozen) while awaiting genetic results. This typically takes 7–14 days.
Genetic Analysis
Biopsied cells are sent to a specialist genetics laboratory, where next-generation sequencing (NGS) is used to analyse all 23 pairs of chromosomes for gains, losses, or structural errors.
Embryo Selection and Transfer
Results categorise each embryo as euploid (chromosomally normal), aneuploid (abnormal), or mosaic (mixed). A euploid embryo is selected for frozen embryo transfer in a subsequent cycle.
Who Is PGT-A Recommended For?
Couples Who May Benefit from PGT-A
- Women of advanced maternal age (typically 37 and over), as aneuploidy rates in embryos increase significantly with age
- Couples who have experienced recurrent implantation failure despite good-quality embryo transfers
- Couples with a history of recurrent miscarriage, particularly where chromosomal causes are suspected
- Couples with a previous pregnancy affected by a chromosomal condition such as Down syndrome
- Men with severely abnormal sperm parameters, where sperm chromosomal abnormalities may be more likely
- Couples who wish to know embryo sex for family balancing or sex-linked medical reasons
Impact on Success Rates
Transferring a euploid embryo significantly increases the chance of live birth per transfer and reduces miscarriage rates, particularly in older women.
Mosaic Embryos
Some embryos may be reported as mosaic — containing a mixture of normal and abnormal cells. Our clinicians will discuss the clinical implications in detail.
Not All Embryos Are Suitable
PGT-A requires embryos to reach the blastocyst stage. Slower-developing embryos may not be suitable for biopsy, which can reduce the number available for testing.
Embryo Sex Determination
PGT-A provides information about embryo sex as part of the chromosomal analysis. This information is shared with patients and can inform transfer decisions where medically appropriate.
Is PGT-A right for your IVF cycle?
Our team will discuss whether PGT-A is clinically indicated for your situation during your consultation. Genetic testing decisions are always made collaboratively and without pressure.
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