Genetic Screening of Embryos

What is Genetic Screening of Embryos?

Genetic Screening of Embryos refers to advanced laboratory testing performed during an IVF cycle to assess the genetic health of embryos before they are transferred into the uterus. This process is commonly known as Preimplantation Genetic Testing (PGT).

PGT allows fertility specialists to identify embryos with the correct number of chromosomes and to detect specific inherited genetic conditions. By selecting embryos that are genetically normal or unaffected by known inherited disorders, the chances of a healthy pregnancy may be improved.

Genetic screening is performed as part of an IVF cycle. After eggs are collected and fertilised in the laboratory, embryos are cultured to the blastocyst stage (typically on day 5 or 6). A small number of cells are carefully removed from the outer layer of the embryo (which later forms the placenta). These cells are then analysed in a specialised genetics laboratory.

The embryo is not damaged during testing when performed by experienced embryologists. After a biopsy, embryos are frozen while awaiting genetic results.

Who is Suitable for Genetic Screening of Embryos?

Genetic screening may be suitable for:

Women over 35 years of age: Chromosomal abnormalities increase with maternal age.
Couples with recurrent miscarriage: Some miscarriages are caused by chromosomal abnormalities in embryos.
Previous failed IVF cycles: Especially when good-quality embryos failed to implant.
Known genetic conditions in the family: Including inherited disorders carried by one or both partners.
Chromosomal rearrangements in either partner: Such as balanced translocations.
Couples seeking to reduce the risk of passing on a known genetic condition.

It is important to note that PGT does not guarantee pregnancy, but it may help identify embryos with a higher chance of successful implantation.

Benefits of Genetic Screening of Embryos

Improved embryo selection: Helps identify chromosomally normal embryos.
Reduced miscarriage risk: By avoiding the transfer of embryos with chromosomal abnormalities.
Higher implantation rates per transfer: Particularly in selected patient groups.
Reduced likelihood of inherited disease transmission: In families with known genetic disorders.
Potential for single embryo transfer: Lowering the risk of multiple pregnancy.

For many patients, especially those undergoing IVF at a later reproductive age, PGT can provide reassurance and more informed decision-making.

Types of Genetic Screening of Embryos

There are several types of PGT, depending on the reason for testing:

PGT-A (Preimplantation Genetic Testing for Aneuploidy): Screens embryos for the correct number of chromosomes. This helps identify embryos with extra or missing chromosomes, such as those associated with Down syndrome.
PGT-M (Preimplantation Genetic Testing for Monogenic Disorders): Used when one or both parents carry a known inherited condition such as cystic fibrosis, thalassaemia, or muscular dystrophy.
PGT-SR (Preimplantation Genetic Testing for Structural Rearrangements): Used when a parent has a chromosomal rearrangement (such as a translocation) that may increase miscarriage risk.
Reproductive Carrier Screening (Pre-conception): Although not performed on embryos, this test checks whether parents carry genes for certain inherited conditions before pregnancy. If both partners carry the same condition, PGT-M may be recommended during IVF.

Dr Wong will recommend the most appropriate type based on your medical history and family background.

Alternative Options to Genetic Screening

Standard IVF without PGT
Prenatal testing during pregnancy (e.g., NIPT, chorionic villus sampling, amniocentesis)
Use of donor eggs or donor sperm
Adoption or other family-building options

Each option has medical, ethical, financial, and emotional considerations. A personalised discussion helps determine the most appropriate approach.

What to Do Before Genetic Screening of Embryos?

Fertility consultation: Review medical, obstetric, and family history.
Genetic counselling: Highly recommended to understand implications, accuracy, and limitations.
Carrier screening (if indicated): Particularly for couples planning PGT-M.
IVF planning: As embryo testing requires IVF to obtain embryos.
Discussion of costs and timelines: Genetic testing adds additional laboratory steps.

Proper counselling ensures that expectations are realistic and aligned with your goals.

What Happens During Genetic Screening of Embryos?

The process involves several stages:

Ovarian stimulation: Hormone injections stimulate the ovaries to produce multiple eggs.
Egg collection: Performed under sedation.
Fertilisation: Eggs are fertilised using conventional IVF or ICSI.
Embryo culture: Embryos develop in the laboratory for 5–6 days.
Embryo biopsy: A few cells are removed from each suitable embryo.
Freezing: Embryos are cryopreserved while awaiting results.
Genetic analysis: Laboratory testing identifies chromosomal or gene abnormalities.
Embryo transfer: A selected embryo is transferred in a later cycle.

Results are usually available within 1–2 weeks.

What to Expect After Genetic Screening of Embryos?

Review consultation: Your doctor will explain the results clearly.
Embryo selection planning: Based on normal, abnormal, or mosaic results.
Frozen embryo transfer cycle: Often scheduled in the following menstrual cycle.
Ongoing pregnancy monitoring: If pregnancy is achieved.

Some embryos may be reported as “mosaic,” meaning they contain both normal and abnormal cells. In selected cases, mosaic embryos may still be considered for transfer following detailed counselling.

Genetic Screening of Embryo Prognosis

Success depends on several factors:

Maternal age
Egg quality
Sperm quality
Uterine health
Underlying medical conditions

PGT may improve the chance of successful implantation per transfer in certain age groups, particularly women over 35. However, it does not increase the number of embryos available — it helps select the most suitable ones.