Both supporters and opponents of abortion rights amongst right-libertarians justify their position on NAP grounds. One question to determine whether or not abortion is consistent with the NAP is at what stage of development a fertilized human egg cell can be considered a human being with the status and rights attributed to personhood. Some supporters of the NAP argue this occurs at the moment of conception while others argue that since the fetus lacks sentience until a certain stage of development, it does not qualify as a human being and may be considered property of the mother. On the other hand, opponents of abortion state that sentience is not a qualifying factor. They refer to the animal rights discussion and point out the argument from marginal cases that concludes the NAP also applies to non-sentient (i.e. mentally handicapped) humans.