The DEXA scan is not recommended while pregnant. The DEXA scan uses low doses radiation to measure body composition which should be avoided whilst pregnant.
A great alternative would be the BOD POD test. The BOD POD measures body composition uses measures whole-body densitometry, fat and fat-free mass, through air displacement. Please note that unlike the DEXA scan, the BOD POD will not give a visceral adipose tissue (VAT) reading, fat mass readings per segment, or a total bone mineral density reading.
To read more about the BOD POD compared to the DEXA, click here.