What difference is that? The size of the chunks?
I will never understand those who draw distinctions on human life...
Why how could you possibly be so medically and scientifically unenlightened in this mega-scientific era? Doncha know that a magical transformation takes place during the short trip down the birth canal? [The doc or midwife says "hocus-pocus" & poof, humanity emerges].
Now for those who believe that personhood begins at viability [whatever that means], we have a worldview exactly for that scenario as well. You see, if Mom wants that baby, he or she is magically converted into a baby. If not, it's an it & remains a blob of cells.
Now for the pre-viability stage understanding, it's all a matter of faith. If you believe in the tooth fairy, Santa Claus, and the Easter Bunny, then certainly you can extend that faith to the womb. We tolerate all faiths here. If, on the other hand, you don't believe in ultrasounds and fetology and anything obstetricians learn in med school about this parasite being a second patient, that's not only fine but fits in better living under the umbrella of omnipotent judges.