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Early intrauterine pregnancy

While scanning urinary bladder in women, we may occasionally encounter sonographic findings suggestive of pregnancy.  The earliest definitive evidence of pregnancy visible on ultrasonography (typically endovaginal) is the gestational sac appearing as a round, anechoic structure surrounded by thickened decidua without visible contents. At this stage, it might be difficult to distinguish true gestational sac from a pseudosac.

However, by the time it is detectable on transabdominal scans (6-7 weeks’ gestation; better seen when the urinary bladder is full), usually there are visible contents (yolk sac, fetal pole) inside the gestational sac. Visualization of a yolk sac is the first definitive evidence of an ‘intrauterine’ pregnancy. Ectopic pregnancies are rarely visible on transabdominal ultrasound but do watch for free fluid in the Morison’s pouch = could be sign of a ruptured ectopic that will likely require surgical intervention. Following are normal transabdominal images of an early intrauterine pregnancy.

Rarely, you may also find intact intrauterine contraceptive device (IUD) alongside the gestational sac (= contraception failure), which warrants immediate referral to the appropriate specialist. Following 2 cases illustrate this phenomenon.


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