What’s the legal status of a child who was conceived after a parent’s death? That question would have been ridiculous not many years ago, but with advances in fertility treatments and the ability to freeze embryos and store sperm for later use, a number of children are now being conceived after one biological parent has passed away.

This has created a number of legal issues. For instance, the Supreme Court recently decided whether twins who were born 18 months after a father’s death were eligible for Social Security survivors’ benefits. (The answer was no, based on the specific language in the Social Security law.)

If someone you know is thinking about freezing embryos or sperm, this may be something to consider in your estate planning. That’s because, if you leave assets in your will to your children, your grandchildren, your nephews and nieces, etc., it’s not always clear whether children who were conceived after a parent’s death will qualify. Not making it clear in your will could potentially lead to a lot of confusion, or even family strife and lawsuits.

If you don’t specify in your will whether children who were conceived after death “count,” then whether they count will be up to state law. Some 17 states say that such children can qualify, but the rules vary. For instance, in Colorado and North Dakota, such children qualify if they were born within 45 months of the biological parent’s death – but not afterward.

Five states say that children who were conceived after death never qualify as children. And the remaining 28 states haven’t adopted any rule at all, which means that determining the children’s legal rights in those states could be extremely difficult.