In IVF, this process of fertilisation happens outside the woman’s body. A woman’s eggs are surgically removed and fertilised in a laboratory using sperm that has been given as a sperm sample. Next, the fertilised egg, called an embryo, is implanted into the woman’s womb.
All IVF treatments begin with a course of hormone therapy to stimulate the development of several follicles in the ovary. These are collected as eggs, which are then fertilised in a test-tube (‘in vitro’) to create several embryos. After between two and five days in an incubator, one or two of these embryos are transferred through the vagina to the uterus, where implantation occurs and pregnancy begins. However, in IVF as in natural conception, not every embryo implants to become a pregnancy, which is why surplus embryos are frozen – so that a subsequent transfer might be tried if the first one fails. Freezing is now an essential part of every clinic’s IVF programme.