What Causes Pain In Lower Abdomen Post Termination Of Pregnancy?

My wife has gone through an abortion of four month due to some defects but she was having some pain in the lower abdomen portion therefore she consulted a doctor who advised her for ultra sound the ultrasound reports are- Uterus is normal in size, anteverted, ateflexed myometrium, texture is normal, endometrial echoes are 6 mm, cervex is hypoechoic