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Consensus statement on Rh pregnancy testing

Rhesus (Rh) immunoglobulin should be given only after 12 weeks gestation for spontaneous abortion, or for medication or uterine aspiration abortion, according to a new consensus statement from the Society of Family Planning (SFP).

The statement, published in the journal Contraception, noted that despite limited historical evidence on whether fetal red blood cell (RBC) exposure during early spontaneous or induced abortion can cause maternal Rh sensitization, “Forgoing Rh immunoglobulin administration before 12 weeks gestation is highly unlikely to increase risk of Rh (D) antibody development.”

For spontaneous or induced abortion care in the first two trimesters of pregnancy, in which the fetus is reasonably certain to be Rh negative, the prescription medicine RhoGAM is not necessary in any scenario or at any gestational age.

The risk of maternal Rh isoimmunization before 12 weeks gestation in patients undergoing spontaneous, medication or uterine aspiration abortion is minimal, according to the consensus statement, due to emerging evidence and improved techniques with greater sensitivity and specificity to quantify fetal red blood cells(RBCs) in maternal blood after abortion.

The costs incurred with routine Rh screening and testing and Rh immunoglobulin administration of pregnant patients before 12 weeks gestation also likely outweigh the benefits, particularly with evolving clinical abortion practices.

Uterine aspiration is the standard of care for uterine evacuation. But sharp curettage is not recommended. In cases where sharp curettage is judged clinically necessary, it is unclear how the procedure might influence the need for Rh immunoglobulin.

Although dissuaded, Rh testing and Rh immunoglobulin administration may be considered for patients less than 12 weeks gestation, at the request of the patient as part of shared decision-making about the patient’s future fertility desires in light of existing data.

For Rh immunoglobulin prior to 12 weeks gestation, a 50 mcg (250 IU) dose of Rh immunoglobulin is recommended.

A 100 mcg dose (500IU) at 12 to 18 weeks gestation is considered safe and effective, which may be available in international settings or can be achieved by giving two 50 mcg (250IU) doses.

The amount of fetomaternal hemorrhage during dilation and evacuation procedures up to 18 weeks gestation is adequately treated with 100 mcg of Rh immunoglobulin.

Continued administration of a 300 mcg (1500IU) dose for patients undergoing abortion after 18 weeks gestation is also encouraged.

However, all patients have the right to decline recommended Rh immunoglobulin testing and administration. Common reasons include no desire for future pregnancy, relative certainty that the patient is Rh-positive, relative certainty that the pregnancy is Rh-negative and the wish to avoid administration of human blood product.

“It is important to document the counseling, recommendation, and declination,” wrote the authors.

Due to the consequences of undertreatment, the recommendations are intentionally conservative, according to the authors, adding that the guidelines will be updated as new evidence surfaces. “As clinics adopt these new guidelines, longitudinal cohort studies should be undertaken to evaluate their uptake and efficacy,” they wrote.

Meanwhile, clinical studies are ongoing to investigate fetal RBC concentration after abortion through 10 weeks in larger populations. The authors advocate similar studies in patients throughout the first and second trimesters.

Reference

Horvath S, Goyal V, Traxler S, et al. Society of Family Planning committee consensus on Rh testing in early pregnancy. Contraception. Published online July 21, 2022. doi:org/10.1016/j.contraception.2022.07.002