A human embryo cannot survive outside the womb on its own, but it can be kept alive in a laboratory for a limited number of days. In IVF clinics, embryos routinely grow in incubators for up to five days after fertilization before they must either be transferred into a uterus or frozen. Beyond that narrow window, no current technology can sustain an embryo through the stages of development that require a placenta and maternal blood supply.
How Long Embryos Survive in an IVF Lab
During in vitro fertilization, eggs are retrieved, fertilized, and placed in incubators designed to mimic conditions inside the body. By day two, the embryo has divided into two to four cells. By day three, it contains six to eight cells. By day five, it has grown into a blastocyst, a cluster of several hundred cells, and this is the point at which it is typically transferred into the uterus or cryopreserved for later use.
Five days is effectively the ceiling for growing a human embryo in a dish under standard clinical conditions. Researchers have pushed this further in experimental settings, culturing embryos for up to 13 days after fertilization, but those studies were halted for ethical reasons rather than because the embryos had stopped developing. A longstanding international guideline known as the 14-day rule prohibits culturing human embryos beyond 14 days or the appearance of the primitive streak, the earliest precursor of the spinal cord. This rule is written into law or formal guidelines in countries including the United Kingdom, Australia, and China, though the International Society for Stem Cell Research has recently proposed loosening it, sparking worldwide debate.
Mouse embryos have been cultured to early organ-formation stages, and non-human primate embryos have been grown in the lab for up to 20 days. These results suggest it may be technically possible to push human embryo culture further, but no one has done so legally.
Why the Uterus Is Essential
The reason an embryo cannot simply keep growing in a dish comes down to what happens during implantation. When a blastocyst reaches the uterus, a sticky protein on its surface binds to carbohydrate molecules coating the uterine wall, gradually slowing it to a stop. Once attached, the outer cells of the embryo send finger-like projections into the uterine lining, tapping directly into the mother’s blood supply. This connection becomes the placenta, the pipeline through which the developing embryo receives oxygen and nutrients and eliminates carbon dioxide and waste.
No incubator can replicate this exchange. A culture dish supplies a nutrient-rich fluid that sustains cell division for those first few days, but it cannot deliver the blood-borne oxygen, hormones, and immune protection that a growing embryo needs once it moves past the blastocyst stage. Without implantation, development stalls.
Frozen Embryos and Long-Term Storage
Cryopreservation is the one way an embryo can exist outside the body for an extended period, though “survive” is a stretch since the embryo is in a state of suspended animation at extremely low temperatures. Embryos frozen within one year of creation have the best outcomes: a clinical pregnancy rate of about 60% and a live birth rate of roughly 49% after transfer. Those frozen for one to six years see pregnancy rates drop to around 53%, with live birth rates falling to about 42%. Beyond six years, outcomes decline further and the risk of ectopic pregnancy rises significantly.
Healthy babies have been born from embryos frozen for well over a decade, so long-term storage is possible. But the data from a study of more than 47,000 transfer cycles shows that shorter freezing durations consistently produce better results. Freezing preserves the embryo but does not improve it, and longer storage appears to carry a higher risk of early miscarriage and preterm birth.
Ectopic Pregnancy: Survival Outside the Uterus Inside the Body
An ectopic pregnancy occurs when a fertilized egg implants somewhere other than the uterus, most commonly in a fallopian tube. In a tubal pregnancy, the embryo cannot survive. The tube is too narrow and lacks the blood supply to support a growing pregnancy, and if left untreated, the expanding tissue can rupture the tube and cause life-threatening bleeding.
In extremely rare cases, an embryo implants in the abdominal cavity rather than the tube and manages to develop a blood supply from surrounding organs. A Medline search covering a decade of medical literature found only 11 reported cases of a secondary abdominal pregnancy reaching a viable gestational age. In one documented case, a live female baby weighing 2.3 kg was delivered from the abdominal cavity at 33 weeks. The baby cried at birth but developed respiratory distress and required intensive care. These cases are medical emergencies, not a viable alternative to uterine pregnancy, and they carry extreme risks to the mother including catastrophic bleeding.
Where Artificial Womb Technology Stands
Several research teams are developing artificial womb systems designed to support premature babies outside the body. The most well-known is the EXTEND system from the Children’s Hospital of Philadelphia, which uses a fluid-filled chamber to simulate the uterine environment. A similar system called EVE was developed by researchers at Tohoku University and the University of Western Australia.
These devices are designed for fetuses between roughly 13 weeks of gestation and full term. They cannot support an embryo from fertilization through the early stages of organ formation. The technology also lacks the placenta’s ability to convert pulsatile blood flow from arteries into the smooth, steady flow needed in the umbilical vein, a technical challenge that has not been solved. No artificial womb has been approved for use in humans, and the long-term psychological and developmental effects on children gestated this way remain entirely unknown.
A concept facility called EctoLife, announced in late 2022, attracted media attention as the “world’s first artificial womb facility,” but it was a conceptual project created by a filmmaker and science communicator, not a functioning medical device. The gap between current technology and a system that could carry a human embryo from fertilization to birth remains enormous.