Where does “одноутробный” come from?

одноутробный (Russian) comes from Russian одно-, from Russian оди́н, from Old East Slavic оди́нъ, from Proto-Slavic edìnъ, from Proto-Balto-Slavic edīˀnas, from Proto-Balto-Slavic aiˀnas, from Proto-Indo-European óynos — one; single.

одноутробный (Russian): having the same mother but a different father, half- of brothers and sisters