So far the spirit soul is concerned, if conditions are for some reason not favorable in some place, he is forced to leave that womb and take shelter in another. And if there is chanting of Hare Krishna, even the soul is there for a short time, oh, he will hear and become advanced. This sound vibration is not material, it is spiritual, and powerful beyond our conception. So it cannot be hindered in any way by something material; it surpasses all these material barriers. So you can know it that when you are chanting, you are also giving benefit to even the child in the womb.
Letter to Mukunda and Janaki, 28 February, 1968