Is mr in pregnancy ok? What does it show that ultrasound does not?

Yes. Yes MRI is safe in pregnancy, it shows more details like fetal brain heart bowels etc which regular ultrasound canot give.
Maternal/fetal MRI. As you can see MRI in pregnancy can show problems not ascertainable by u/s: fetal nervous system lesions; fetal lung/tracheoesophageal lesions; fetal palate defects; conjoined twin pathology; maternal appendicitis/urolithiasis; maternal retroperitoneal pathology. It is not only ok but indispensable in the evaluation of the black box that is the gravid abdomen and its precious contents.