First Trimester Miscarriage Evaluation

Ruth B. Lathi, M.D.; Florette K. Gray Hazard, M.D.; Amy Heerema-McKenney, M.D.; Joanne Taylor, M.S., C.G.C.; Jane Tsung Chueh, M.D.

Disclosures

Semin Reprod Med. 2011;29(6):463-469. 

In This Article

Ultrasound Evaluation

With the increased availability of ultrasound, patients are receiving earlier sonographic diagnoses, and it is more precise to describe unsuccessful or failed pregnancies based on their sonographic appearance with "embryonic demise" referring to cases where the ultrasound clearly shows an "embryonic fetal pole" without cardiac activity. Anembryonic miscarriage is defined by sonography as an empty gestational sac at a gestational age where one would expect to see a yolk sac or embryo with cardiac activity.

When evaluating an early pregnancy by ultrasound, one must be familiar with the timing and sequence of normal embryonic development. An embryonic pole with cardiac activity equates to a gestational age of at least 6 weeks. If an embryonic pole is not seen, the potential gestational sac should be examined for the double decidual sac sign (double echogenic ring) within the endometrial cavity, which can help differentiate a true gestational sac from a pseudosac. This can be seen as early as 4 weeks of gestation.[1–3] If the sac lacks this sign and appears as an endometrial fluid collection, one must suspect a pseudogestational sac. In this case, the differential includes the nonpregnant state, a very early intrauterine pregnancy (IUP), or ectopic pregnancy, and the ultrasound findings should be correlated with serial quantitative hCG measurements. Theoretically, a true gestational sac can be distinguished from a pseudogestational sac by its appearance and location, and should be confirmed with a mean sac diameter (MSD) ≥10 mm.[4,5] However, before clear visualization of this sign, differentiation of a true versus pseudogestational sac can be difficult. In the absence of symptoms suggesting ectopic pregnancy, a follow-up ultrasound should be considered to avoid terminating a potentially viable pregnancy. Additionally, hCG levels can be helpful in distinguishing between an early IUP and an ectopic pregnancy, and hCG values between 1500 and 2000 mIU/mL are typically associated with a visible intrauterine gestational sac on transvaginal scan.[6–8]

As the pregnancy matures, a yolk sac becomes visible on transvaginal scan by 8 mm MSD or by 20 mm MSD on transabdominal scan.[9] Cardiac activity is often the earliest sign of the developing embryo and can typically be seen transvaginally when MSD ≥16 mm or transabdominally when MSD ≥25 mm.[10] Sonographic diagnosis of embryonic demise can be made when there is no cardiac activity in an embryo ≥5 mm by transvaginal ultrasound or ≥9 mm by abdominal ultrasound.[11] Given the possibility of measurement error, it is prudent to allow an additional 1 to 2 mm in gestational sac measurement before considering intervention or repeat the ultrasound in 1 week if the embryonic size is near this cutoff.[11]

Signs that may be associated with a higher rate of embryonic demise include slow heart rate, small gestational sac size or abnormal shape, presence of subchorionic hematoma, presence of embryonic anomalies, and abnormalities in intervillous blood flow. Benson and Doubilet found that 60% fetuses with heart rates <90 at <7 weeks of gestation died before the end of the first trimester.[12–16] Bromley et al found that 94% of embryos with a small gestational sac (defined as the difference between the mean sac diameter and crown rump length [CRL] <5) resulted in miscarriage, despite the presence of normal fetal cardiac rate.[17] Ultrasound-documented subchorionic hematomas also correlate with miscarriage, with rates varying between 7.7% and 18.8%, depending on the size of the hematoma.[18] Women who present with bleeding and a subchorionic hematoma at ≤8 weeks of gestation are at higher risk of miscarriage than those with bleeding after 8 weeks of gestation (13.7% versus 5.9%).[19] Odeh et al compared gestational sac volumes between normal pregnancies, missed embryonic miscarriages, and anembryonic miscarriages. They found that gestational sac volume was significantly smaller in both embryonic and anembryonic miscarriages compared with normal pregnancies.[20] Whether three-dimensional (3D) volumes offer advantages over conventional ultrasound parameters in the prediction of miscarriage remains to be tested by a large prospective trial.

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