factor where there is history of miscarriage. Age of gametes at the time of fertilization has been shown to have no effect on low birth weight or preterm delivery. Viability and established pregnancy A related issue that comes up in this debate is how often fertilization leads to an established, viable pregnancy. Research in in-vitro fertilization patients suggests that fertilized embryos fail to implant some 30% to 70% of the time, although it is unknown whether this rate corresponds to inherently low human implantation rates (in natural conception) or to an altered physiological state. Of those that do implant, about 25% suffer early pregnancy loss by the sixth week LMP (after the woman's Last Menstrual Period), and an additional 7% miscarry or are stillborn. As a result, even without the use of birth control, between 50% and 70% of zygotes never result in established pregnancies, much less birth. Ethics of preventing implantation The intention of a woman to prevent pregnancy is an important factor in whether or not the act of contraception is seen as abortive by some anti-abortion groups. Hormonal contraceptives have a possible effect of preventing implantation of a blastocyst, as discussed previously. Use of these drugs with the intention of preventing pregnancy is seen by some anti-abortion groups as immoral. This is because of the possibility of causing the end of a new human life. However, hormonal contraception can also be used as a treatment for various medical conditions. When implantation prevention is unintentionally caused as a side effect of medical treatment, such anti-abortion groups do not consider the practice to be immoral, citing the bioethical principle of double effect. Likewise, when a hormonal contraceptive is used with the intention of preventing fertilisation, the intended reduction in implantation failures, miscarriages and deaths from childbearing may outweigh the possibility that the method might cause some implantation failures. A related application of the principle of double effect is breastfeeding. Breastfeeding greatly suppresses ovulation, but eventually an ovum is released. Luteal phase defect, caused by breastfeeding, makes the uterine lining hostile to implantation and as such may prevent implantation after fertilization. Some pro-choice groups have expressed concern that the movement to recognize hormonal contraceptives as abortifacient will also cause breastfeeding to be considered an abortion method. Detectable pregnancy A protein called early pregnancy factor (EPF) is detectable in a woman's blood within 48 hours of ovulation if fertilization has occurred.