What is PGD?
Pre-Implantation Genetic Diagnosis (PGD) and Pre-Implantation Genetic Screening (PGS/PGT-A) are techniques used during IVF to test embryos for genetic conditions or chromosomal abnormalities before they are transferred to the uterus. This allows us to select embryos with the highest potential for a healthy pregnancy.
Who Needs Genetic Testing?
- Carriers of genetic conditions — Couples who carry genes for conditions like cystic fibrosis, sickle cell disease, thalassemia, or Huntington's disease
- Previous chromosomally abnormal pregnancy — History of Down syndrome or other chromosomal conditions
- Recurrent miscarriage — Repeated pregnancy losses potentially due to chromosomal factors
- Repeated IVF failure — Multiple unsuccessful embryo transfers despite good quality embryos
- Advanced maternal age — Women over 37 have higher rates of chromosomally abnormal embryos
- Known chromosomal translocation — Balanced translocations that increase risk of unbalanced offspring
- Sex-linked conditions — Genetic conditions that affect one sex more than another
How Does PGD/PGS Work?
1. Standard IVF Cycle
The process begins with a normal IVF stimulation cycle, egg retrieval, and fertilisation (usually with ICSI to avoid contamination with foreign DNA).
2. Embryo Biopsy
On day 5-6, when embryos reach the blastocyst stage, our embryologist removes a small number of cells (5-10) from the trophectoderm — the outer layer that will become the placenta. This does not harm the inner cell mass that becomes the baby.
3. Genetic Analysis
The biopsied cells are sent to a specialised genetics laboratory for analysis. Results are typically available within 1-2 weeks. During this time, embryos are vitrified (frozen) to await results.
4. Embryo Selection & Transfer
Once results are available, only embryos that are genetically normal (for the tested condition) and chromosomally balanced are selected for frozen embryo transfer.
Carrier Screening
Before embarking on PGD, both partners undergo carrier screening — blood tests that identify whether you carry genes for specific inherited conditions. This information determines which conditions to test embryos for and ensures that PGD is technically feasible for your specific genetic situation.
Common conditions screened in South Africa include:
- Cystic fibrosis
- Sickle cell disease
- Thalassemia
- Spinal muscular atrophy
- Fragile X syndrome