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SAN DIEGO -- Frequent fetal heart monitoring is not needed in every pregnant woman testing positive for anti-SSA/anti-Ro autoantibodies, but it's definitely advisable for those with high titers, interim results of a new trial indicated.

These data should help clinicians determine which pregnant patients should get weekly or biweekly monitoring to look for fetal atrioventricular block (AVB), according to Jill Buyon, MD, of NYU Langone Health in New York City, and colleagues writing in . Their study is also to be presented at the American College of Rheumatology's annual meeting that started here Friday.

Fetal monitoring is not hugely expensive or difficult but still represents a burden during an already stressful time for pregnant persons. In their paper, Buyon and colleagues cited "the physical, emotional, and economic burden of serial echocardiographic monitoring, which most often only detects irreversible third-degree atrioventricular block."

It has nevertheless been suggested for all those with positive anti-SSA/anti-Ro tests thanks to previous studies linking them to increased risk for fetal AVB. This condition is associated in turn with higher rates of damaging cardiac arrhythmias in infants after delivery.

These antibodies help drive autoimmune conditions such as lupus and Sjögren's syndrome. But people can have the antibodies without such diseases. It's been unclear whether even low titers predict fetal AVB or if there is some threshold level, below which testing is not worthwhile.

Buyon and colleagues may have answered the question with their ongoing study, called , whose is to test the efficacy of intravenous immune globulin and dexamethasone to reverse second-degree fetal AVB when detected. A total of 1,300 women positive for anti-SSA/anti-Ro antibodies are to be enrolled, with final results expected in 2026.

As of this past August, 413 women were enrolled and underwent fetal heart monitoring conducted weekly, biweekly, or on some other regular schedule according to local standards. (Fetal outcomes have yet to be analyzed.) For the interim analysis focusing on potential threshold antibody titers, the researchers stratified patients into two groups defined by antibody titers of <1,000 ELISA units (low) versus ≥1,000 units (high).

No fetal AVB was seen in any pregnancy in the 152-member group with low titers. Among the 261 with high titers, 10 showed fetal AVB, a rate of 3.8%.

Some 31,000 Doppler recordings were made in the study, with just 45 showing abnormal fetal heart rates. Seven fetuses had second-degree AVB, one had second- or third-degree block, two had definite third-degree AVB, and 17 had premature atrial contractions. Eighteen showed normal rhythms on urgent testing.

Some 8% of the high-titer group quit monitoring after the first week, citing the burden. Their infants all had normal echocardiograms after birth. The rest of the group averaged 2.3 readings per surveillance day, with a median of 2.8.

Overall, the results suggested that something like one-third of pregnant women with positive autoantibody tests can be excused from regular fetal heart monitoring. The testing might still be a challenge for those with high titers as established in this analysis.

"While the [monitoring] in part was meant to empower participants, reliable readings necessitated review by an on-call cardiologist, which may be challenging to implement in a real-world setting. This limitation supports the need to program the Doppler devices to identify which readings require urgent echocardiograms," Buyon and colleagues noted.

Another issue is that standard commercial tests for anti-SSA/anti-Ro antibodies are not as quantitatively precise as the research-type used in the current study. "For example, many patients were referred for enrollment based on positivity in the BioPlex assay, in which the analytic measurable range at the high end is limited to >8 without any further titration," the researchers cautioned. "This interpretation of potential high titer by being >8 was below the STOP BLOQ risk threshold in a fifth of cases, none of which developed AVB."

An important limitation of the study was the low number of fetal AVB detections.

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