In vitro fertilisation

In vitro fertilisation is the procedure in which eggs are recovered from ovaries, combined with sperm in a laboratory dish, cultured for a few days, and transferred to a uterus as an embryo. It is the oldest and most widely performed of the assisted reproductive technologies, and its reach extends far beyond infertility medicine. Almost every technique this wiki covers under reproduction, from Embryo selection to Human germline editing, is an operation on an embryo that exists only because of IVF.

§How a cycle works

A cycle runs in four steps: stimulation, egg collection, fertilisation and culture, transfer. Injected gonadotrophins stimulate the ovaries to mature many follicles at once, where a natural cycle matures one. Ultrasound and blood hormone measurements track the response, and eggs are collected under sedation by a needle passed through the vaginal wall. In the laboratory the eggs are either mixed with prepared sperm or, where sperm quality is poor, injected with one sperm each by intracytoplasmic sperm injection (ICSI). Fertilised eggs are cultured for two to six days, usually to the blastocyst stage. One embryo is transferred; the rest are vitrified and stored.

Two changes have reshaped that sequence since the 1990s. ICSI, first reported by a Brussels group in 1992, made severe male-factor infertility treatable and is now used in a majority of cycles worldwide, including many where the indication for it is unclear.¹ Vitrification, an ultra-rapid cooling method that avoids ice crystal formation, made frozen embryo and egg storage reliable enough that transferring a thawed embryo in a later cycle is now often preferred to transferring a fresh one. Cryonics proposes to apply the same physical principle to a whole body; in IVF it works on a hundred-micrometre object with no vasculature.

§Development history

1. 1959
   Rabbit IVF confirmed
   Min Chueh Chang produces live rabbit young from eggs fertilised in vitro, establishing that mammalian fertilisation outside the body can yield normal offspring.
2. 1978
   Louise Brown
   Patrick Steptoe and Robert Edwards report the first human birth after in vitro fertilisation, achieved in an unstimulated cycle with a single egg.
3. 1990
   Preimplantation testing
   Alan Handyside's group biopsies human embryos and selects by sex to avoid X-linked disease, opening the field of embryo testing.
4. 1990-1991
   Statutory regulation in the UK
   The Human Fertilisation and Embryology Act creates a licensing authority with a fourteen-day limit on embryo culture, the model most later regimes were measured against.
5. 1992
   ICSI
   A single sperm injected directly into an egg produces pregnancies, extending treatment to men with almost no motile sperm.
6. 2010
   Nobel Prize
   Robert Edwards receives the Nobel Prize in Physiology or Medicine; Steptoe had died in 1988 and the prize is not awarded posthumously.
7. 2012
   Egg freezing leaves the experimental category
   Vitrification results are judged good enough for the American Society for Reproductive Medicine to drop the experimental label from oocyte cryopreservation, and elective egg banking becomes a commercial market.

§What it delivers

The age of the egg is the dominant variable, and success rates fall steeply through the late thirties and forties. Success is also better described per patient across several cycles than per transfer, so a well-run clinic quotes a cumulative live-birth rate.

Volume is now substantial. An analysis of four decades of international registry data put the number of children born after assisted reproduction between 1978 and 2018 at between roughly 9.8 and 13 million, with several million more since.² UK licensed clinics ran more than 77,500 IVF cycles for 52,400 patients in 2023, producing almost 21,000 babies, about one UK birth in thirty-two; the multiple birth rate fell to 3.4% as single embryo transfer became standard.³ The fall in multiple births is an underrated public-health result, because twin pregnancies carry much of the obstetric risk historically attributed to IVF itself.

Why this article sits in the middle of the reproduction portal

Every embryo technology covered here operates on an embryo outside a body. Polygenic embryo screening ranks embryos, Mitochondrial replacement therapy rebuilds one, heritable editing would rewrite one, and In vitro gametogenesis would supply the eggs to make far more of them. None of them has an independent route to a pregnancy. IVF delivers all of them, so its cost, its regulation and the number of embryos a cycle yields set the practical limits on each.

§The platform other technologies stand on

Embryo biopsy and testing are the clearest case. Preimplantation genetic testing for monogenic disease is reliable and uncontroversial where a couple carries a known variant. Testing for aneuploidy is performed on a large share of cycles in some markets, and randomised trials have not shown that it raises live-birth rates per patient.⁴ Polygenic screening extends the same biopsy to complex traits and is rejected as unvalidated by professional genetics bodies.

Beyond selection, IVF is the necessary substrate for anything that edits or reconstructs an embryo. The He Jiankui affair was carried out inside ordinary IVF cycles with ordinary equipment, using CRISPR–Cas9 reagents that can be ordered. That is what makes governance hard: the specialised part of heritable editing is a reagent, and the rest is a clinic of the kind that exists in most countries. In vitro gametogenesis, if it works in humans, would remove the binding constraint on embryo number and change what selection could deliver. Spare and donated embryos are also the starting material for human embryonic stem cell lines and for much of what is known about early human development. That dependence is part of why induced pluripotent stem cells and embryo models were pursued at all; each reduces the need for donated embryos without removing it.

§Add-ons and the evidence problem

IVF is largely a private market even in countries with public health systems, and it sells optional extras: endometrial scratching, immunological treatments, time-lapse incubation, assisted hatching. The UK regulator rates these on a published scale and, at its 2023 overhaul, placed none of the thirteen it had reviewed in the category reserved for treatments shown by multiple good trials to improve live-birth rates.⁵ The scale itself has been criticised for compressing very different kinds of uncertainty into one colour, but its central finding is not seriously disputed: patients pay for interventions that mostly have not been shown to work.

What a success rate does not show

A clinic's headline rate depends on which patients it accepts and how it counts. Rates per embryo transferred exclude cycles cancelled before transfer; rates per cycle started include them. Neither figure describes an individual's chance, which is dominated by age and by cause of infertility.

§Risks and outcomes for children

Ovarian stimulation carries a small risk of ovarian hyperstimulation syndrome, which has become less common with milder protocols and freeze-all strategies. Egg collection is a minor surgical procedure with the usual bleeding and infection risks.

For the children, the risks are real but small, and hard to attribute to a cause. A systematic review and meta-analysis found birth defects modestly more common after assisted reproduction than after natural conception.⁶ Preterm birth and low birthweight are likewise somewhat more frequent. Nobody has fully separated the contributions of the laboratory procedures, the parents' underlying subfertility, and the multiple pregnancies that were common in earlier practice. The same ambiguity attaches to the slightly raised rate of imprinting disorders. Follow-up now extends to adults in their forties without a signal that would change clinical practice.

§Access, law and cost

Regulation ranges from statute to nothing. The United Kingdom licenses clinics and specifies what may be tested for; several European states restrict embryo creation and storage tightly; the United States regulates laboratories and advertising but leaves the substance of practice to professional guidance. The gaps between these regimes drive reproductive travel, and they are the gaps analysed under Access and inequality. Where the law does bind, it can bind in unexpected places. The fourteen-day limit on embryo culture written into the UK statute in 1990 was set at a point nobody could then reach, and it is now the constraint that the work described under Ectogenesis and embryo modelling runs into.

Funding is where the differences matter most. In the UK the NHS-funded share of cycles fell from 35% in 2019 to 27% in 2023, with wide regional variation.³ Elsewhere, cost is the binding constraint on who has children this way, and it carries through to every downstream capability: a technology priced as an add-on to a self-funded cycle is available only to people who can already afford the cycle.

The legal status of the embryo is unsettled in a way that can disrupt practice overnight. In February 2024 the Supreme Court of Alabama held that frozen embryos are children under the state's wrongful-death statute; several clinics suspended treatment, and the legislature passed immunity legislation within three weeks.⁷ The episode is the clearest recent demonstration that IVF's stability rests on a legal settlement about embryo status that is neither uniform nor secure. Every technology built on top of IVF inherits that exposure.

§See also

• Embryo selection
• Polygenic embryo screening
• In vitro gametogenesis
• Mitochondrial replacement therapy
• Human germline editing
• Reproductive longevity
• Artificial womb
• Uterus transplantation

§References