In discriminating between a viable and non-viable early intrauterine pregnancy, which one of the following criteria can be used to reliably diagnose pregnancy failure? a. crown-rump length < 7 mm and no heartbeat b. mean gestational sac diameter of > 25 mm and no embryo c. absence of embryo with heartbeat 3-5 days after an ultrasound scan that showed a gestational sac with a yolk sac d. an enlarged yolk sac (> 7mm)

The correct answer in discriminating between a viable and non-viable early intrauterine pregnancy is B: "Mean gestational sac diameter of > 25 mm and no embryo".

Explanation:

There are different criteria used to discriminate between a viable and a non-viable early intrauterine pregnancy. The most often used to diagnose pregnancy failure are:

-         Crown-rump length criterion: This is the absence of cardiac activity by the time the embryo has reached crown-rump length. A crown-rump length of 7 mm or more with no cardiac activity has been suggested by the latest studies to diagnose a non-viable pregnancy. There is a substantial likelihood that a crown-rump length < 7 mm can result in a false-positive diagnosis of pregnancy failure.

-         Mean sac diameter criterion: This is the absence of embryo by the time the gestational sac has grown to a certain size. The gestational sac increases as the pregnancy progress. It has been suggested by the latest studies to use a mean sac diameter of 25 mm or more, and no visible embryo to diagnose failed pregnancy. A mean sac diameter of 16 to 24 mm and no embryo is suspicious for failed pregnancy, but shouldn’t be used to diagnose it.

-         Time-based criteria: This is the absence of an embryo by a certain point in time. If an initial sonogram shows that there is a gestational sac and a yolk sac, but about 11 days later there isn’t any embryo with cardiac activity, then a failed pregnancy can be established. The timing event in early pregnancy is precise and reproducible to perform a correct diagnosis.  

There are also suspicious findings that may help to identify a non-viable pregnancy. These are not certain and have not been extensively studied yet, so they cannot be used to reliably diagnose a pregnancy failure. A few of these findings are an empty amnion, a small gestational sac size, and the yolk sac size.

-         Yolk sac: An enlarged yolk sac sized over 7 mm is suspicious for a failed pregnancy.