In vitro fertilization or IVF has been producing babies since 1978 when the first ‘test tube baby’ was born. The process then was fairly simple and did not change much for quite a while. The egg and sperm are placed in a special fluid in a Petri dish where fertilization occurs. Then the fertilized egg starts to divide. By the end of the first day there are two cells where previously there had been one. This is the zygote stage. With the passage of another day the zygote has four cells. One more day and the cell count is now up to six to nine cells and the zygote undergoes a major change. Before the third day the cells are dividing using the DNA information from the mother’s genes. At this point the embryo starts using its own unique combined DNA to determine further cell division in order to move on to the next stage. In the early days of IVF the embryos were routinely transferred into the uterus at three days because they would not survive beyond that time period in the artificial fluid. Now researchers have found that progressively changing the media, as the fluid is called, allows the zygote to grow into a blastocyst. A blastocyst develops about day 5 post-fertilization. By day 4 the zygote has started looking like a berry, round and consisting of between 16 and 32 cells. Before this stage all the cells were basically identical, but now they are starting to differentiate at this stage, called the morula. The blastocyst stage usually starts on day 5, the cells developing into three distinct parts: a central hole filled with fluid called the blastocele inner cells lining the central blastocele, called the Inner Cell Mass, which ultimately become the fetus the outer cells on the surface, the trophectoderm, which will develop into the placenta. Most IVF experts now prefer to wait until the cells have reached the blastocyst stage before transferring into the mother. The reason for this is that only 35% to 40% of embryos actually survive to become a fetus. As a consequence transferring at day 3 post-fertilization resulted in pregnancy only about one third of the time unless multiple zygote were implanted. And that raises the chances of a multiple pregnancy with all the complications that can occur. Because of advances in technology, waiting until day 5 is now possible. By day 5 the morulas that have advanced to the next stage are much more likely to produce a pregnancy. Therefore only a few blastocysts are necessary for the transfer. The ‘poorer’ quality embryos have died off because of genetic mistakes, especially chromosomal abnormalities, leaving only the healthiest and strongest ones with the best potential for success. Transferring only one or two blastocysts markedly decreases the chances of multiple fetuses, producing twins, triplets or more. The procedure for transferring into the uterus is the same whether the transfer takes place on day 2 or 3 or day 5 or 6. But the rate of successful pregnancies is greatly enhanced by waiting for blastocyst development. In addition the later transfers reduce the miscarriage rate, since the fetuses are developing from the ‘best’ genetic material. IVF does not produce a baby with every transfer. However scheduling the transfer on day 5 or 6 results in a pregnancy more than 60% of the time in women younger than 37 and over half the time in women even as old as 42. IVF specialists want the same thing their patients do, a healthy pregnancy and a healthy baby. Using the techniques developed in the past decade they are getting very satisfactory results, producing pregnancies for people who truly want children.