Ultrasound plays a key role in evaluating women with threatened abortion since HCG levels do not correlate well with a specific diagnosis. Large perigestational hemorrhages have been associated with pregnancy loss while smaller perigestational hemorrhages usually resolve without sequelae. A large gestational sac without a visualized embryo is unequivocal evidence of a failed, anembryonic pregnancy. As stated previously, all embryos greater than 5 mm should demonstrate cardiac activity. Embryonic demise should be diagnosed only after careful observation by two experienced people, preferably sonographer and physician, for at least 3 minutes.
Embryonic bradycardia is a poor prognosticator of pregnancy viability and needs follow-up.
Growth retardation is easily detected by comparing the MSD with the CRL or by following the growth of these parameters serially. The early gestational sac grows approximately 1mm per day. The most reassuring sign that an ectopic pregnancy is not present is the sonographic demonstration of a normal intrauterine pregnancy. A variety of uterine findings can be seen with ectopic pregnancies. This should not be confused with an intrauterine gestational sac.