Munich has a brief but good pregnant sex scene.
Movies with real pregnant bellies:
https://letterboxd.com/belliesrlovely/list/real-pregnant-bellies/share/O8XqXaBHPipuZmCL/detail
https://letterboxd.com/belliesrlovely/list/real-pregnant-bellies/share/O8XqXaBHPipuZmCL/detail