since the precursors of the major organ systems are now developing. Each cell of the preimplantation embryo has the potential to form all of the different cell types in the developing embryo. This cell potency means that some cells can be removed from the preimplantation embryo and the remaining cells will compensate for their absence. This has allowed the development of a technique known as preimplantation genetic diagnosis, whereby a small number of cells from the preimplantation embryo created by IVF, can be removed by biopsy and subjected to genetic diagnosis. This allows embryos that are not affected by defined genetic diseases to be selected and then transferred to the mother's uterus. Sacrococcygeal teratomas, tumours formed from different types of tissue, that can form, are thought to be related to primitive streak remnants, which ordinarily disappear. First arch syndromes are congenital disorders of facial deformities, caused by the failure of neural crest cells to migrate to the first pharyngeal arch. Spina bifida a congenital disorder is the result of the incomplete closure of the neural tube. Vertically transmitted infections can be passed from the mother to the unborn child at any stage of its development. Hypoxia a condition of inadequate oxygen supply can be a serious consequence of a preterm or premature birth. See also Embryo loss Aorta-gonad-mesonephros CDX2 Development of the reproductive system Development of the urinary system Developmental biology Drosophila embryogenesis Embryomics Gonadogenesis Human tooth development List of human cell types derived from the germ layers Potential person Recapitulation theory The Human Embryo Additional images References External links Virtual human embryo Photo of blastocyst in utero Slideshow: In the Womb Embryology Human biology