Conjoined twins can be diagnosed using standard ultrasound as early as 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 functioning of their organs. False-positive results can occur before 10 weeks, however, when identical twins who share an amniotic sac (monoamniotic twins) may appear conjoined.
If an ultrasound detects conjoined twins, a magnetic resonance imaging (MRI) scan may be done. It can provide greater detail about where the conjoined twins are connected and which organs they share.
April 10, 2013
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