The reasons for unwanted childessness are numerous, but so are the means for treating them. The technique of in-vitro fertilization, or IVF, removes several eggs from the ovary for fertilization in the laboratory. After a few days, one or two of these fertilized eggs, which are now known as embryos, are returned to the uterus in the hope that they implant and become a pregnancy. Women who are having IVF are given special reproductive hormones to encourage several eggs to develop within the ovaries. Further maturation of the egg itself is induced by the administration of a further hormone. Thirty-six hours later fluid containing the eggs is drawn from the ovary with a needle. This is usually performed under light sedation, in a short out-patient procedure, with the doctor using ultra-sound to check proceedings. The eggs collected from the ovary are then mixed with a sample of the male partners sperm, which has already been washed and concentrated. The eggs and sperm are left in an incubator set at 37 degrees for 24 hours so that fertilization can take place. During this time, only one of the many sperm cells will penetrate the outer layer of the egg and achieve fertilization. Following fertilization, the cells divide and multiply and form an embry. After two or three days, a healthy embryo will comprise around eight cells. It is then transferred to the uterus by means of a thin flexible tube, where it is left to implant and form a pregnancy.