PGD, or preimplantation genetic diagnosis, is a technique used during IVF to test embryos for specific genetic conditions before they’re transferred to the uterus. If you or your partner carry a known genetic disorder, PGD allows doctors to identify which embryos are affected and select only unaffected ones for transfer. The term PGD has been officially replaced in clinical practice by PGT-M (preimplantation genetic testing for monogenic disorders), though many patients and clinics still use the older name.
PGD, PGT-M, and PGT-SR Explained
The umbrella term now used is PGT, or preimplantation genetic testing. It covers three distinct types of testing, each targeting a different kind of genetic problem:
- PGT-M (monogenic disorders): This is what was formerly called PGD. It tests for single-gene conditions passed from parent to child, such as cystic fibrosis, sickle cell disease, Huntington’s disease, or BRCA-related cancer syndromes.
- PGT-SR (structural rearrangements): This tests embryos when one parent carries a chromosomal rearrangement like a translocation or inversion. These rearrangements often cause recurrent miscarriages or infertility.
- PGT-A (aneuploidy): This screens for embryos with the wrong number of chromosomes overall. It’s used broadly in IVF, not just for known genetic carriers.
When people search for “PGD in IVF,” they’re almost always asking about PGT-M or PGT-SR, since both involve testing embryos for a condition that runs in the family.
Conditions PGD Can Detect
PGT-M targets single-gene disorders where the specific mutation is already known. The most common reasons couples pursue this testing include autosomal recessive conditions like cystic fibrosis and hereditary hemoglobinopathies (such as sickle cell disease and thalassemia), where both parents carry one copy of the faulty gene. For autosomal dominant conditions, where inheriting just one copy causes disease, the most frequent indications are myotonic dystrophy type 1, neurofibromatosis, Huntington’s disease, and hereditary cancer syndromes like those linked to BRCA1 or BRCA2 mutations.
X-linked disorders are also commonly tested. These include Duchenne muscular dystrophy, hemophilia, and fragile X syndrome. Because these conditions are carried on the X chromosome, they disproportionately affect male offspring, and PGT-M can identify which embryos inherited the mutation regardless of sex.
For couples where one partner carries a balanced chromosomal rearrangement, PGT-SR serves a related but distinct purpose. A large multicenter study of over 1,200 carrier couples found that the most common rearrangements were reciprocal translocations (about 81% of cases), followed by Robertsonian translocations, inversions, and insertion translocations. Among the babies born after PGT-SR in that study, 73% had completely normal karyotypes, meaning they didn’t inherit the parental rearrangement at all.
How the Biopsy Works
PGD requires removing a small number of cells from each embryo for analysis. This biopsy happens on day 5 or 6 of embryo development, when the embryo has reached the blastocyst stage and contains two distinct cell types: the inner cell mass (which becomes the baby) and the trophectoderm (which becomes the placenta). Cells are taken only from the trophectoderm, leaving the inner cell mass untouched.
The process involves either creating a small opening in the embryo’s outer shell on day 3 or 4 and waiting for cells to herniate through, or using a direct suction technique at the blastocyst stage. A laser is used to separate roughly 5 to 10 trophectoderm cells from the rest of the embryo. Research suggests that around 8 cells provides the most reliable DNA for analysis, though the general consensus targets about 5 cells as a minimum.
After the biopsy, the cells are sent to a genetics lab while the embryos are frozen through vitrification. Results typically come back within 7 to 14 days. Because of this waiting period, PGD cycles nearly always involve a frozen embryo transfer rather than a fresh one. Once results are back, you’ll begin preparing your uterine lining with hormones, and once it reaches adequate thickness (usually monitored by ultrasound), the transfer is scheduled. This means the full timeline from egg retrieval to embryo transfer is roughly 10 to 12 weeks.
Accuracy of Results
PGT is highly reliable for clear-cut results. A large meta-analysis found that when a biopsy identifies an embryo as chromosomally normal, that result is confirmed about 94% of the time. When an embryo is flagged as abnormal, the result holds up roughly 89% of the time. The misdiagnosis rate after transferring an embryo deemed normal is less than 1%, sitting at about 0.2% across studies.
The one area where accuracy drops significantly is with mosaic embryos, which contain a mix of normal and abnormal cells. Mosaic results are confirmed only about 53% of the time, and when mosaic embryos are transferred, roughly 22% result in a completely normal pregnancy. This means mosaicism on a biopsy report doesn’t necessarily reflect what’s happening in the rest of the embryo, and your clinic may discuss whether transferring a mosaic embryo makes sense in your situation.
Impact on Pregnancy Outcomes
A single-center retrospective study comparing PGT cycles to conventional IVF found a live birth rate of 46% in the PGT group versus 35% in the conventional IVF group. Miscarriage rates were also notably lower: about 31% of clinical pregnancies in the PGT group ended in miscarriage compared to 43% in the conventional group. These differences were statistically significant.
The improvement makes intuitive sense. By screening out embryos with genetic abnormalities or chromosomal imbalances before transfer, PGD reduces the chance of implanting an embryo that would either fail to develop or result in miscarriage. For couples with known genetic conditions or chromosomal rearrangements, who often have higher baseline miscarriage rates, this benefit can be especially meaningful.
Cost of PGD Testing
PGD/PGT-M adds a significant expense on top of a standard IVF cycle. The testing itself typically costs between $3,000 and $6,000 per cycle, though prices vary widely by lab and location. Some estimates place the upper range above $12,000 when accounting for complex cases or additional testing platforms. On top of the testing fee, PGD cycles require embryo freezing and a frozen embryo transfer, which adds further cost compared to a fresh transfer cycle. In total, PGD adds roughly $6,000 or more to the cost of an IVF cycle.
One factor that can increase expense is the need for a custom probe or test design. For PGT-M specifically, the genetics lab often needs to develop a personalized testing protocol based on your family’s specific mutation. This setup process can take several weeks and may carry its own fee before the IVF cycle even begins. Insurance coverage for PGD varies considerably, with some plans covering it for medically indicated genetic conditions and others excluding it entirely.
Risks to the Embryo
The biopsy itself carries a small risk of damaging the embryo. Modern trophectoderm biopsy at the blastocyst stage is considerably safer than older techniques that removed cells from day-3 embryos, though it is not risk-free. The combination of biopsy and freezing can reduce embryo survival rates compared to embryos that are frozen without being biopsied. Early research found that only about 33% of biopsied embryos had at least half their cells intact after freeze-thaw, compared to 55% of unbiopsied controls. However, vitrification technology has improved dramatically since those early studies, and current survival rates after biopsy and vitrification are much higher in modern labs.
The other practical risk is that PGD may leave you with fewer embryos to transfer. Some embryos won’t survive the biopsy, some will yield inconclusive results, and some will be identified as affected or abnormal. For couples who produce a small number of embryos per cycle, this attrition can mean needing multiple IVF retrievals before having a transferable embryo.