The law and technology are always in a state of tension, since technology can evolve quickly and the law may drag behind. Often we find ourselves trying to apply decades or centuries-old legal rules to a totally new situation, and sometimes it is hard to find the right answer.
Such is the case with new reproductive technologies and wills, trusts, and estate law. Reproductive technologies such as in-vitro fertilization make it possible for people to procreate much later in life and in some cases even have a child after they have already passed. This presents problems in several aspects of estate planning.
For example, what happens if a couple decides to store sperm or frozen embryos in order to have more children at a later date, and then one of the spouses passes away and subsequently the other decides to have the children? These children could not have been planned for in a will or trust document unless the couple had specifically discussed this eventuality and there is a provision addressing unborn children.
In the situation where there is no provision, the court must go back and look at well established laws likely written several decades ago and then make a decision as to whether the children are "heirs" under the meaning of the statute. At the time the laws were made the drafters probably would not have predicted this situation, so it will be up to the judgment of those interpreting the law at the time to decide.
As one can see from this example, there will be a lot of uncertainty if posthumously concieved children are not planned for in advance. This is why couples considering saving sperm, eggs, or embryos should address the issue in their will or trust documents.
Source: New York Times, "Fertility Treatments Produce Heirs Their Parents Never Knew," Paul Sullivan, Aug. 30, 2013.