In 1977, British biochemist Frederick Sanger and his colleagues became the first people in history to read, start to finish, the complete genetic code of a living organism. That organism wasn't human, or even a mouse — it was a tiny bacteriophage called φX174, a virus that infects E. coli. Its entire genome ran to just 5,375 base pairs, the letters of the genetic code. Even so, it took Sanger's team months of painstaking manual work to read that sequence, step by step. The method behind it, now known as Sanger sequencing, earned him his second Nobel Prize.
The human genome is roughly 600,000 times longer than that virus's — about 3.2 billion base pairs. When the international Human Genome Project launched in 1990, decoding a single complete human genome took thirteen years and, by various estimates, somewhere between $2.7 and $3 billion. Today, a complete human genome can be read in a single day for under a thousand dollars — some labs are already pricing it below $200. It's one of the steepest price collapses in the history of science, and it's exactly what turned WGS — whole genome sequencing — into a practical tool for ordinary clinics, not just major research institutions.
In conversations about reproductive health, terminology gets tangled fast: karyotyping, PGT-A, carrier panels, exome, whole genome — to anyone outside the field, it all sounds like the same generic "genetic test." In reality, these are methods with fundamentally different depth and fundamentally different jobs.
Karyotyping is the oldest method, over sixty years old by now — it simply shows the number and gross structure of chromosomes under a microscope. PGT-A, which we covered in an earlier article, also counts chromosomes, but does so at the embryo level before an IVF transfer. A carrier screening panel checks a few hundred specific, already-known mutations linked to common hereditary conditions — fast and inexpensive, but it only sees what's already on the list. Whole exome sequencing reads roughly 1 to 2% of the genome — the regions that directly code for proteins. And whole genome sequencing reads literally everything: all 3.2 billion base pairs, including vast stretches whose function still isn't fully understood.
| Method | What it checks | Typical use |
|---|---|---|
| Karyotyping | Chromosome count and gross structure | Classic diagnosis of chromosomal syndromes |
| PGT-A | Chromosome count in an embryo | Embryo selection before transfer in IVF |
| Carrier screening panel | A few hundred specific, already-known mutations | Screening donors and couples before conception |
| Whole exome sequencing (WES) | All protein-coding regions (about 1–2% of the genome) | Finding the cause of a rare, previously undiagnosed condition |
| Whole genome sequencing (WGS) | All 3.2 billion base pairs, including non-coding regions | The most complete picture available, for research and complex clinical cases |
Modern WGS has almost nothing in common with Sanger's manual 1977 method. DNA is first physically chopped into a huge number of short fragments, and each fragment is read in parallel alongside millions of others — this is the principle behind next-generation sequencing, or NGS. Specialized software then reassembles millions of short reads into a single sequence, like an enormous jigsaw puzzle, and compares the resulting genome against a reference human genome, flagging every difference. Those differences — known as variants — are what a doctor or genetic counselor is actually interested in.
For most people planning a pregnancy through donation, IVF, or natural conception, WGS isn't usually the first or even a necessary step — a carrier screening panel, which covers the main common conditions at a noticeably lower cost, is generally enough for routine screening. But there are situations where the depth of a full genome analysis is genuinely justified.
The depth of WGS is both its strength and a source of new complications. The more of the genome gets read, the more variants of uncertain significance turn up — sequences that differ from the reference but whose health impact science simply doesn't fully understand yet. Receiving that kind of result without preparation can feel more unsettling than useful: you're left holding information that can't be cleanly interpreted one way or the other.
A second complication is incidental findings. While analyzing a genome for one reason, it's entirely possible to stumble on a predisposition to a completely unrelated condition — an elevated hereditary cancer risk, for instance, that had nothing to do with the original purpose of the test. That's why reputable labs and clinics always arrange a genetic counseling session before a whole-genome test and discuss in advance which categories of findings a patient wants to know about and which they'd rather not — this is formally known as the right not to know, and it's written into the ethical guidelines of most professional genetics bodies.
Just a decade ago, WGS was seen as a rare, expensive tool reserved for the toughest diagnostic puzzles. That's shifting toward much broader use. The UK, the US, and several countries in Asia now run pilot programs for whole-genome screening of newborns — instead of the standard heel-prick blood test covering a few dozen conditions, a baby's entire genome is sequenced and checked against hundreds of rare hereditary conditions, many of which can be treated starting in the first weeks of life if caught early enough.
A similar logic is gradually making its way into donor screening in reproductive medicine: major international donor banks increasingly offer expanded genetic panels approaching WGS-level coverage, rather than sticking to a standard list of a few dozen conditions. For a couple choosing a donor, that means the real possibility of comparing their own genomic profile against the donor's and spotting overlap on rare recessive mutations that a narrower carrier panel might simply have missed.
While the underlying technology is the same everywhere, the infrastructure and regulation around how whole-genome sequencing results get used in medicine vary considerably from country to country.
| Country | Access to WGS in a reproductive context | Notable detail |
|---|---|---|
| United Kingdom | Widely available | The national 100,000 Genomes Project set a standard for the whole health system |
| Spain | Available, mostly through private labs | Often bundled with donor programmes |
| Germany | Available with restrictions | Genetic diagnostics law governs which findings can be disclosed to patients |
| France | Available at specialised centres | Use outside strict medical indications is tightly restricted |
| Denmark | Available | Strong research base in genomics |
| Portugal | Available, mostly paid | Growing market of private genetic labs |
| Czech Republic | Available | Noticeably cheaper than in Western Europe |
| Israel | Widely available | One of the world's leaders in integrating genomics into clinical practice |
| Brazil | Available, mostly in major cities | Demand rising alongside the broader fertility market |
| Greece | Available | Often bundled with donor programmes |
| Cyprus | Available | Growing as part of the medical tourism sector |
| Ukraine | Available | One of the most affordable sequencing markets in Europe |
Following the launch of the national 100,000 Genomes Project in 2012, the UK built genomic sequencing into the standard workings of the NHS more deeply than most other European countries. Germany and France, much as with PGT-A, take a more cautious approach: legislation strictly governs which genetic findings can be disclosed to a patient and under what conditions. The Czech Republic and Ukraine stand out for affordability, making them popular destinations for patients looking to combine expanded genetic screening with a more limited budget.
The journey from a tiny virus's 5,375 base pairs in 1977 to three billion base pairs of human genome read in a day for a few hundred dollars is, arguably, one of the clearest illustrations of how fast science can move once there's enough demand behind it. But speed of technology doesn't mean every patient needs the most exhaustive analysis available: the choice of method — anywhere from a simple panel to a full genome — should always follow the specific clinical question at hand, not a trend toward whichever test sounds the most thorough.