Conjoined twins can be diagnosed using standard ultrasound as early as the end of the first trimester. More-detailed ultrasounds and echocardiograms can be used about halfway through pregnancy to better determine the extent of the twins' connection and the functioning of their organs.

If an ultrasound detects conjoined twins, a magnetic resonance imaging (MRI) scan may be done. The MRI may provide greater detail about where the conjoined twins are connected and which organs they share.