Early induced abortion not a risk factor for Rh sensitization

Key takeaways:

• Few participants undergoing first trimester abortion had elevated fetal red blood cell counts.
• Not administering Rh immunoglobulin during the first trimester could safely save time and money.

Induced abortion during the first trimester did not increase risk for Rh sensitization, which suggests that Rh testing and treatment in pregnancy is unnecessary before 12 weeks gestation, researchers reported in JAMA.

Up to 10% of women who test Rh-negative become sensitized to Rh with each full-term pregnancy, according to study background. Physicians can prevent Rh sensitization with Rh immunoglobulin when Rh-negative patients are exposed to significant volumes of Rh-positive blood, the researchers wrote, but there is a lack of evidence for whether maternal exposure to fetal red blood cells exceeds the threshold for Rh sensitization in induced first-trimester abortion.

“Rh immunoglobulin is traditionally given whenever a patient experiences bleeding during pregnancy, if they are Rh negative — which is true for about 15% of people in the U.S.,” Sarah Horvath, MD, MSHP, FACOG, assistant professor of obstetrics and gynecology in the department of obstetrics and gynecology at Penn State University College of Medicine, told Healio. “We have great data that supports giving Rh immunoglobulin in the third trimester and at delivery, but not for patients with bleeding in the first trimester.”

Horvath and colleagues conducted a multicenter, observational, prospective cohort study with 506 participants (mean age, 27.4 years; 61.9% Black) who were undergoing induced first-trimester abortion care before 12 weeks gestation. Researchers utilized high-throughput flow cytometry to detect circulating fetal red blood cells in paired maternal blood samples before and after induced abortion in the first trimester.

Overall, 319 participants underwent medical and 187 participants underwent procedural abortion at less than 12 weeks gestation. At baseline, three participants had elevated fetal red blood cell counts and, of these, one had elevated fetal red blood cell counts after abortion. Researchers observed no other participants with elevated fetal red blood cell counts above the sensitization threshold following induced abortion during the first trimester.

From baseline, the median change was 0 per 5 million fetal red blood cells with upper 95th and 99th percentiles of 24 and 35.6 per 5 million fetal red blood cells, respectively. Researchers also noted a strong association between the pre- and postabortion fetal red blood cell counts, but no other baseline characteristics were significantly associated with fetal red blood cell counts after induced abortion.

“Cost analyses will bolster the argument for aligning professional medical society guidelines around this new, compelling evidence,” Horvath said.

“It can be difficult to think about not doing something in medicine that has been done for 50 years, but that practice [administering Rh immunoglobulin] was based on expert opinion and not supported by robust evidence. The only way to provide equitable care for all is to provide high value care and not spend money on care without proven benefit,” she said.

For more information:

Sarah Horvath, MD, MSHP, FACOG, can be reached at sarahkate824@gmail.com.