Conclusion

Generally, it is safe to engage in exercises during pregnancy. However, the type of exercises you do matter a lot. Sit-ups or crunches are considered to be safe only during the first trimester of pregnancy. They contribute to the development of diastasis recti, but they do not affect your baby.
You should talk to your doctor and ask for advice about the type of exercises you should engage in during pregnancy and also after the birth of your baby.
References
[1] https://en.m.wikipedia.org/wiki/Amniotic_fluid
[2] https://www.healthline.com/health/diastasis-recti
[3] https://en.wikipedia.org/wiki/Inferior_vena_cava
[4] https://en.wikipedia.org/wiki/Rectus_abdominis_muscle
[5] https://en.wikipedia.org/wiki/Linea_alba_(abdomen)
[6] https://en.wikipedia.org/wiki/Transverse_abdominal_muscle











