the Ericsson Method for artificial gender selection. The Ericsson method separates male and female sperm by passing them through a column filled with blood protein, human serum albumin. As the sperms enter the human serum albumin, the differences in mass between the X and Y chromosomes manifest as the lighter male sperms push deeper into the protein than the females dragged down by the weight of the extra "leg" of the X sex chromosome. This tiny difference creates separate layers of concentrated male and female sperm. The layers of gender-selected sperm are of higher concentrations but not pure. This lack of purity explains the 30% chance of gender selection failure of the Ericsson method. IVF/PGD technique After ovarian stimulation, multiple eggs are removed from the mother. The eggs are fertilized in the laboratory using the father's sperm in a technique called in vitro fertilization (IVF). "In vitro" is Latin for "within glass". Fertilized eggs are called embryos. As the embryos develop through mitosis, they are separated by sex. Embryos of the desired sex are implanted back in the mother's uterus. Prior to fertilization with IVF, the fertilized eggs can be genetically biopsied with preimplantation genetic diagnosis (PGD) to increase fertilization success. Once an embryo grows to a 6-8 cell size, a small laser incision in the egg membrane (zona pellucida) allows safe removal of one of the cells. Every cell in the embryo contains an identical copy of the genome of the entire person. Removal of one of these cells does not harm the developing embryo. A Geneticist then studies the chromosomes in the extracted cells for genetic defects and for a definite analysis of the embryo's sex. Embryos of the desired sex and with acceptable genetics are then placed back into the mother. The IVF/PGD technique is favored over the Ericsson method because of the stricter control of the sex of the offspring in the laboratory. Since only embryos of the desired sex are transferred to the mother, IVF/PGD avoids the small likelihood present in the Ericsson method of an undesired sperm fertilizing the egg. Sex selection success rates for IVF/PGD are very high. The technique is recommended for couples who will not accept a child of the undesired sex. Timing methods Timing methods aim to affect the sex ratio of the resultant children by having sexual intercourse at specific times as related to ovulation. Studies have not been