Haematoma can occur in pregnancy. Adrenal mass detected during pregnancy is very uncommon. Because pheochromocytoma in pregnancy is associated with high mortality and morbidity, it always to be excluded. Because of nonenhanced and non hormonal nature of mass, pheochromocytoma is very unlikely in this patient. However contrast CTScan of whole abdomen will be helpful in this case.. MRI of abdomen will be also helpful. Cortisol estimation to done after delivery to look for late development of hypofunction of adrenal which can occur after adrenal haemorrhage to avoid adrenal crisis. 

http://www.healthhype.com/adrenal-hemorrhage-bleeding-gland.html

https://www.npeu.ox.ac.uk/ukoss/current-surveillance/atp

Thank you. I will check it. I'll send the MRI images ASAP

Benign adrenal tumor is most likely