How do doctors diagnose amniotic sac disorders?

Ultrasound: Many but not all disorders are noted during sonograms, especially while monitoring twin or other multiple pregnancies. Some can not be determined till birth.

Ultrasound : By amniotic sac disorders i assume you mean amniotic band syndrome. This is a condition whereby a segment of the amnion is separated from the uterine wall. Early in pregnancy parts of the fetus can become entrapped in this membrane and cause amputations. This is diagnosed and followed by ultrasound.