In July 1990, something happened at Hammersmith Hospital in London that would reshape reproductive medicine — and, almost by accident, sway a parliamentary vote along the way. A team led by Alan Handyside and Robert Winston announced the world's first successful pregnancy resulting from genetic testing of an embryo before transfer. Two couples faced a high risk of passing on X-linked hereditary conditions to their children, so embryologists biopsied a single cell from each embryo at the 6-to-8-cell stage, determined sex through PCR, and transferred only the embryos at no risk of the disease. News of the pregnancy broke just five days before a decisive vote in the British Parliament on embryo research legislation — and, by most accounts at the time, it helped sway MPs who'd been leaning toward an outright ban.
Since then, the method — first called preimplantation genetic diagnosis, now known more broadly as preimplantation genetic testing, or PGT — has come a long way. It started out narrow, checking embryos for one specific known mutation at a time. Fairly quickly, though, fertility specialists began asking an obvious follow-up question: what if you checked the entire chromosome set instead of just one gene? That question gave rise to PGT-A — aneuploidy screening, the search for extra or missing chromosomes.
The umbrella term PGT actually covers several quite different tests, and the resulting confusion is one of the main reasons people end up looking for clarification. PGT-M (monogenic) checks an embryo for one specific, already-known single-gene mutation — cystic fibrosis, Huntington's disease, or a BRCA mutation already identified in the family, for instance. PGT-SR (structural rearrangements) looks for chromosomal rearrangements — translocations and inversions — in couples where one partner carries a balanced rearrangement. PGT-A (aneuploidy) checks the total chromosome count in the embryo: instead of the expected 46 chromosomes arranged in 23 pairs, an embryo might carry an extra or missing copy of one of them.
Extra or missing chromosomes are, by far, the most common genetic reason an embryo fails to implant, a pregnancy ends early, or a child is born with a condition such as Down syndrome (trisomy 21). The share of aneuploid embryos rises sharply with maternal age: in women under 35, roughly one embryo in three turns out abnormal; past 40, that figure climbs to more than half.
In the original 1990s protocols, biopsy happened on day three of embryo development, when the embryo is just six to eight cells — one or two cells were removed, a fairly risky operation for such a fragile structure. Today's standard is trophectoderm biopsy on day five or six, once the embryo reaches the blastocyst stage and has grown to a hundred cells or more. At that point, a handful of cells can be safely removed from the outer layer — the trophectoderm, which will go on to form the placenta rather than the fetus itself — significantly cutting the risk of harming the embryo while improving the accuracy of the test.
The first generation of chromosome-screening tests relied on FISH (fluorescence in situ hybridization), which could only check a handful of chromosomes at once — typically five to nine out of twenty-three pairs. That meant a chunk of abnormalities simply went undetected. By the 2000s, comparative genomic hybridization (array CGH) took over, finally allowing all 23 chromosome pairs to be screened at once. And since the early 2010s, next-generation sequencing (NGS) has become the gold standard — it covers the full chromosome set and can also pick up subtler patterns, including mosaicism, where a single embryo contains a mix of normal and abnormal cells.
This is where the story gets genuinely interesting — and far less clear-cut. For years, PGT-A was marketed on the promise that selecting "genetically normal" embryos would automatically boost both transfer success rates and the odds of a healthy baby. Large randomized trials in recent years, including the well-known STAR trial, haven't borne that out across the board: for young patients with a good prognosis, the cumulative live birth rate per started IVF cycle turned out roughly comparable whether or not PGT-A was used.
Mosaic embryos add a further wrinkle. They used to be automatically discarded as abnormal, but accumulated data now show that transferring some mosaic embryos can result in perfectly healthy babies — the abnormal cells sometimes get quietly weeded out as the embryo develops further. That's why leading reproductive medicine bodies, including Europe's ESHRE, now advise against automatically discarding mosaic embryos and instead recommend assessing each one individually — and, more broadly, advise against offering PGT-A routinely to every patient regardless of their situation.
None of this means the test is useless — for the specific groups listed above, the evidence for benefit is considerably stronger. But the decision to do PGT-A is best made with a doctor, weighing your own clinical picture rather than a clinic's general marketing promises.
For MAPASGEN users, PGT-A tends to come up in three recurring contexts. First, with donor eggs: a young, healthy donor does statistically lower the risk of aneuploidy, and that's genuinely true — but even donors aged 22 to 28 still produce some embryos with an extra or missing chromosome, which is why clinics often offer PGT-A as an added filter before transfer, especially when there's only one shot at this with a limited number of embryos.
Second, when planning a single embryo transfer — say, when a couple or a single parent deliberately chooses to transfer one embryo rather than two, specifically to avoid the risks of a multiple pregnancy. In that situation, the test helps identify which of several embryos has statistically better odds of implanting successfully, cutting down on wasted waiting cycles.
Third, PGT-A comes up for couples where one partner carries a balanced chromosomal rearrangement: strictly speaking, that calls for PGT-SR rather than PGT-A, but many labs today combine both analyses into a single panel, since NGS technology can extract this expanded chromosomal information from one biopsy without any additional intervention on the embryo.
Unlike ovarian reserve testing, the legal status of PGT-A isn't purely a medical question anymore — it's become a political one. Countries differ sharply on the idea of selecting embryos by chromosome count, and the resulting regulation is far from uniform.
| Country | PGT-A status (aneuploidy screening) | Notable detail |
|---|---|---|
| Spain | Permitted | One of Europe's largest PGT-A markets |
| United Kingdom | Permitted | Regulated by the HFEA, offered at most IVF clinics |
| Greece | Permitted | A popular destination for IVF combined with genetic screening |
| Germany | Banned | Patients travel to the Czech Republic or Spain for PGT-A |
| France | Banned (PGT-M for a specific known disease is allowed on medical grounds) | Tightly controlled through specialised prenatal diagnosis centres |
| Denmark | Restricted | Historically cautious stance, regulation revisited periodically |
| Portugal | Permitted on medical grounds | Used alongside other IVF protocols |
| Czech Republic | Permitted | A popular destination for foreign patients |
| Israel | Permitted | Widely used alongside other genetic screening methods |
| Brazil | Permitted | Governed by the professional reproductive medicine council |
| Cyprus | Permitted | Often paired with competitively priced IVF |
| Ukraine | Permitted | Widely available as part of standard IVF protocols |
Germany and France remain among the most restrictive countries: PGT-A is fully banned in Germany, while France only permits testing for one specific, already-known disease in couples with a serious hereditary history — that's PGT-M, not routine aneuploidy screening. This is part of why German and French patients frequently choose clinics in Spain or the Czech Republic, where PGT-A is a standard, readily available option. Spain, the UK, and Greece, by contrast, sit among the countries with the most open regulation and well-developed infrastructure for embryo genetic screening.
Still, it's worth understanding that even where PGT-A is legal and technically accessible, leading medical bodies increasingly call for selective rather than blanket use, not a default add-on for every IVF cycle. The road from that first embryo biopsy in 1990 to today's ongoing debate over the real value of full chromosomal screening is a story not just of technological progress, but of reproductive medicine's slow ethical maturing: each new generation of the method forces a fresh answer to the same underlying question — which piece of information about an embryo genuinely helps parents make a meaningful decision, and which just offers the illusion of control in a place where biology still leaves real uncertainty.