DENVER – There is a slew of ultrasound findings that are equivocal or downright worrisome for the diagnosis of early pregnancy failure, but the list of definitive findings is short – and even those are fraught with controversy, according to Dr. Roxanne Vrees.
"In a highly desired pregnancy, even with ultrasound findings that are perhaps suggestive of early pregnancy failure, I think watchful waiting has a really important role," said Dr. Vrees, an ob.gyn. at Brown University in Providence, R.I.
She is also on the staff at the Women and Infants Hospital in Providence, where she works in a unique women’s emergency department staffed 24/7 exclusively by ob.gyn. attending physicians. Traditional emergency medicine physicians are not in the picture. This busy women’s ED averages nearly 30,000 visits annually, so Dr. Vrees and her colleagues have acquired considerable experience in emergency ob.gyn. However, because the facility is licensed by the state as an ED, by law any patient who comes in must be treated, so medical backup is available around the clock for patients who present with chest pain or otherwise fall outside the generalist ob.gyn.’s scope.
Early pregnancy failure occurs in 15%-20% of clinically recognized pregnancies. The most common symptom is vaginal bleeding, which occurs in one-quarter of all known first-trimester pregnancies, half of which end in pregnancy failure.
Dr. Vrees emphasized that no single aspect of the work-up for early pregnancy failure should drive patient management. That ought to be based upon a combination of the patient’s symptoms, laboratory findings, physical exam, and pelvic ultrasound.
In the setting of worrisome ultrasound findings, the most important step in management is to get a repeat ultrasound under real-time observation. The use of cine loops in order to visualize the entire gestational sac is valuable.
"Most obstetricians underutilize this. You’re unlikely to miss a yolk sac or embryo, and you’re getting a true report of sac diameter, not a random measurement from a snapshot," she explained at the annual meeting of the Society of Ob/Gyn Hospitalists.
Worrisome but nondefinitive findings suggestive of early pregnancy loss include a slow fetal heart rate, an unusual appearance of the uterine lining, and a sac that is small, grossly distorted, enlarged, irregularly contoured, or low in position.
Maternal gestational age is a key consideration in defining a slow fetal heart rate by M-mode ultrasound. At a menstrual age of 6.2 weeks or less, a normal fetal heart rate is 100 bpm or more; less than 90 bpm is considered slow. In contrast, at 6.3-7.0 weeks, normal is defined as 120 bpm or more, and a fetal heart rate of less than 110 bpm is considered slow. When a slow fetal heart rate is detected at 6.0-7.0 weeks, the risk of subsequent first-trimester fetal demise remains elevated at about 25% even if the heart rate is normal at follow-up at 8.0 weeks (Radiology;2005;236:643-6).
The absolute ultrasound criteria for early pregnancy failure used at the Women and Infants Hospital as well as in many other settings are no fetal heart beat in an embryo more than 5 mm in crown-rump length, or menstrual age known to be greater than 6.5 weeks with no heart beat.
However, a group of investigators led by Dr. Yazan Abdallah of Imperial College London has argued that current definitions used to diagnose early pregnancy failure are potentially unsafe and could result in inadvertent termination of wanted pregnancies. Given the inherent inter- and intraobserver variation in ultrasound measurements, they have urged more conservative criteria for the definitive diagnosis of early pregnancy failure: specifically, a crown-rump length cutoff of greater than 7 mm instead of the widely used 5 mm, and a mean gestational sac diameter cutoff of more than 25 mm.
Dr. Abdallah and his coworkers support their argument on the basis of their observational, prospective cross-sectional study involving 1,060 consecutive women diagnosed with intrauterine pregnancy of uncertain viability. This diagnosis was based upon a symptom-generated ultrasound that showed either an empty gestational sac; a gestational sac with a yolk sac but no embryo when the mean gestational sac diameter was either less than 20 mm or less than 30 mm; or an embryo with an absent heart beat and a crown-rump length of either less than 6 mm or less than 8 mm.
The primary endpoint was a viable pregnancy upon routine first-trimester screening ultrasound at 11-14 weeks. At that point, 473 of the women had viable pregnancies and 587 did not.
When neither the yolk sac nor the embryo was visualized on the initial ultrasound, the false-positive rate for diagnosis of early pregnancy failure was 4.4% when a mean gestational sac diameter of 16 mm was used as a cutoff and 0.5% when 20 mm was the cutoff. Only when a cutoff of 21 mm was utilized did the false-positive rate fall to 0.