First Trimester Pregnancy Complication

5.1 Early Pregnancy Failure

Description and Clinical Features

The rate of pregnancy loss is highest in the first trimester, especially before 8 weeks gestation. A number of terms have been used to describe this event early in pregnancy, including “early pregnancy failure,” “early pregnancy loss,” “blighted ovum,” “spontaneous abortion,” and “missed abortion.” The first two of these are gaining general acceptance.

Early pregnancy failure may present clinically with pain, cramping, and bleeding (a symptom complex termed “threatened abortion”). Some early pregnancy losses are due to chromosomal anomalies, and other cases are thought to result from abnormalities of the corpus luteum or subclinical intrauterine infection. Most pregnancy failures, however, have no identifiable cause.

Sonography

Transvaginal sonographic findings that are definitive for early pregnancy failure include:

Embryo with crown–rump length of at least 7 mm and no embryonic heartbeat (Figure 5.1.1).
Gestational sac with mean sac diameter of at least 25 mm and no visible embryo (Figure 5.1.2).
No embryo with heartbeat seen on a scan performed at least 2 weeks after a sonogram that demonstrated a gestational sac without yolk sac or embryo.
No embryo with heartbeat seen on a scan performed at least 11 days after a sonogram that demonstrated a gestational sac with yolk sac (Figure 5.1.3).

Transvaginal sonographic findings that are suspicious, but not definitive, for early pregnancy failure include:

Embryo with crown–rump length less than 7 mm and no embryonic heartbeat (Figure 5.1.4).
Gestational sac with mean sac diameter of 16–24 mm and no visible embryo (Figure 5.1.5).
No embryo with heartbeat seen on a scan performed 7–13 days after a sonogram that demonstrated a gestational sac without yolk sac.
No embryo with heartbeat seen on a scan performed 7–10 days after a sonogram that demonstrated a gestational sac with yolk sac.
No embryo with heartbeat seen on a scan performed at least 6 weeks after the last menstrual period.
Empty amnion (amnion seen adjacent to yolk sac, with no visible embryo) (Figure 5.1.6).
Enlarged yolk sac (at least 7 mm in diameter) (Figure 5.1.7).

If any of these suspicious findings is present, pregnancy failure should be suspected and a follow-up sonogram should be performed to confirm the diagnosis. In general, the follow-up scan should take place 7–10 days later.

Figure 5.1.1 Definite pregnancy failure. Transvaginal sonogram demonstrates an intrauterine gestational sac with an embryo (calipers) whose crown–rump length measures 7.4 mm. No cardiac activity was seen on real-time sonography.

Figure 5.1.2 Definite pregnancy failure. Transvaginal sonogram demonstrates an intrauterine gestational sac whose mean sac diameter (calipers) is 27.7 mm, calculated as the average of 35.4 mm and 19.7 on the sagittal (SAG) image (A) and 28.1 mm on the coronal (COR) image (B). There is a yolk sac (arrow) but no embryo is seen.

Figure 5.1.3 Definite pregnancy failure. A: Transvaginal sonogram demonstrates an intrauterine gestational sac (arrow). B: The sac contains a yolk sac (arrowhead) but no embryo is seen. C: On follow-up sonogram 12 days later, the yolk sac (arrowhead) is again seen, but there is still no embryo or heartbeat.

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