<prompt> Pseudogestational sac is seen inMissed aboionThreatened aboionInevitable aboionEctopic pregnancy  <response>: The gestational sac --an anechoic fluid collection that represents the exocoelomic cavity--may be seen by 4.5 weeks.A caveat is that a gestational sac may appear similar to other intrauterine fluid accumulations--the so-called pseudogestational sac. This pseudosac may be seen with ectopic pregnancy and is easier to exclude once a yolk sac is seen. Typically, the yolk sac is visible by 5.5 weeks and with a mean gestational-sac diameter of 10 mm. Thus, the diagnosis of a uterine pregnancy should be made cautiously if the yolk sac is not yet seen.Ref: William;s Obstetrics; 24th edition; chapter 19 