No, it’s not immaterial. As unborn are too vaporous population to take account of in censuses, so they are too uncertain personae to be the subjects of personal rights. For one thing is that some courts, even many of them, find occasion to assign singular rights to them, and a very different one that courts in general acknowledge them full personal rights.
Note, for instance, that full personal rights would entail police research of the circumstances in which every natural abortion occurs. Was the pregnant woman negligent? Perhaps, she smoked too much, drank too much, lent herself to excess stress, and so on. If such was the case, she must be charged with negligent homicide. Perhaps, she took due care, but someone else it was who had a dispute with her that provoked the accident. That one would be accused of negligent homicide. Criminal prosecution would become unmanageable. And so forth possibly with other branches of the law.