In vitro fertilization, also known as IVF, is a treatment in which a female patient’s eggs are fertilized with a male patient’s sperm (or a sperm donor) in the lab before being transferred back to the uterus. This procedure allows doctors to bypass the fallopian tubes, making it an excellent choice for patients with blocked, damaged, or absent fallopian tubes. It also requires just one sperm cell for each egg, enabling successful fertilization even in cases of the most severe male infertility. And generally, because it allows for the simultaneous use of multiple eggs without an inherent risk of multiple pregnancy, it is the most powerful and successful treatment for all forms of infertility, including age-related infertility and unexplained infertility.

Because IVF is most successful when doctors can attempt fertilization on a larger number of eggs, a female patient is typically placed on a course of ovary-stimulating medications to prompt her body to produce multiple eggs in one cycle. The patient is monitored over a period of 8–11 days with ultrasounds and blood work. Then, when the eggs are sufficiently mature, they are retrieved from the patient’s ovaries in a brief surgical procedure during which she is placed under sedation.

The sperm from the male patient or a sperm donor is prepared through a process called “sperm washing,” which isolates healthy sperm from the remainder of the seminal fluid in order to improve chances of fertilization. The sperm is then combined with the egg in the laboratory under careful observation to promote fertilization. In some cases, the doctors may recommend a procedure called intracytoplasmic sperm injection, or ICSI, in which a single sperm is injected directly into the egg.

After the eggs are fertilized to create one or more embryo(s), they are incubated in a specialized, finely tuned environment in the lab for 5–6 days. Embryologists will monitor and support them to ensure they are developing properly.

At this stage, patients may opt for a “fresh embryo transfer,” which means that one or two of the healthiest-looking embryos will be transferred back into the female patient’s uterus. If the procedure is successful, an embryo will implant into the uterus and the patient will be pregnant. If there are additional normal-appearing embryos available, they can be preserved for future use via a specialized process of cryopreservation called embryo freezing.

Frequently, patients opt to have test embryos for normal genetics and identify abnormalities, such as Down syndrome, before embryo transfer. This process is known as preimplantation genetic screening (PGS) or preimplantation genetic diagnosis (PGD). If PGD/PGS is being implemented, after visual inspection and assessment under the microscope, all viable-appearing embryos undergo a procedure called trophectoderm biopsy, in which a microscopic amount of material is obtained and sent to the genetics lab for analysis. Typically, all embryos biopsied will be frozen immediately, before the results of the PGD/PGS testing are available; the embryos will then be selected for embryo transfer in the context of a frozen embryo transfer (FET).