embryo manipulation or IVF (for example, mouse, goat and pig) still have a very low reproductive cloning efficiency, with prenatal and early postnatal losses [19-23; 29; 50]. Moreover, until the molecular basis of LOS is known, it is not possible to say that the syndrome would not occur in human reproductive cloning attempts.

Animal cloning can also result in danger to the mother of any cloned offspring. Increased maternal morbidity and mortality can result from late gestational fetal loss, increased size of the fetus, abnormal placentation, pregnancy toxemia, and, most notably, hydroallantois and/or hydramnios (excessive fluid accumulation in the uterus often associated with fetal abnormality and maternal distress) [6; 8-11; 16]. These effects have been seen most prominently in studies with cattle and sheep. For example, in the cattle cloning study by Hill et al. (1999) [8], four of the 13 pregnant cows and their fetuses died because of complications late in pregnancy. Tim King and Ian Wilmut (pers. comm.) have noted that hydroallantois can affect up to 5% of established sheep pregnancies involving cloned offspring, although this condition is “extremely rare” in normal pregnancies. Documentation of these and related maternal problems appears to be relatively sparse in the literature, possibly because the focus of research has been on the cloned offspring rather than the pregnant cows.

In conclusion, if results from animal reproductive cloning studies are extrapolated to humans, they suggest that reproductive cloning of humans could carry a very high risk to the health of both fetus or infant and mother and lead to associated psychological risks for the parents as a consequence of late spontaneous abortions or the birth of a stillborn child or a child with severe health problems. Moreover, if the cloned human fetus or placenta grew abnormally large, this could cause problems before a cesarean section would be an option, particularly if multiple embryos are placed in the uterus, which is the procedure in most IVF clinics in the United States. There is no reason, at this time, to expect the efficiency of implantation to be better for reproductive cloning than IVF.

Failures in several aspects of mammalian development are likely to contribute to the defects observed in cloned animals, and probably no one cause is responsible for all the problems. Some of the processes that are likely to be suboptimal have been enumerated [1; 2] and are outlined in the final sections of this chapter. Two processes, reprogramming and imprinting, are thought to be especially problematic [32; 38; 51].