In every country with whose citizenship laws I have some familiarity, the child is subject to the same jurisdictions as the parent, since children (especially infants} have no legal capacity to accept or reject legal jurisdiction of a nation. In exceptional cases the child can be taken away from the parent and becomes a ward of the state. In that case the child is subject to the jurisdiction of the state. If the child is unborn it does not come under the jurisdiction of the US at the time the mother crosses our border. The issue of birthright citizenship does not apply to unborn children of illegal alien mothers. However, if you are referencing the abortion question, the born, unborn distinction is much more significant.
Nothing relating to birth applies to any unborn child. But every born person is subject to US jurisdiction once they enter the US. Since there is no way to be unborn, jurisdiction is established during birth.