Postdelivery levels of anti-D IgG prophylaxis in D- mothers depend on maternal body weight.

BACKGROUND

Current recommendations for anti-D prophylaxis for women who deliver a D+ offspring vary from country to country, and the introduction of new reagents require pharmacokinetic studies that show serum levels after the injection. Serum levels of anti-D may depend on the maternal body mass index (BMI).

STUDY DESIGN AND METHODS

Serum concentrations of total anti-D IgG and IgG1-4 subclasses were determined by flow cytometry in 26 D- women, who had received prophylaxis after delivery of a D+ offspring. Blood samples were drawn on Days 1, 2, 3, and 14 after injection, and the BMI was recorded.

RESULTS

Anti-D levels increased continuously in all women during the first 3 days. The increase was significantly affected by the BMI if higher than 27 kg per m2 (p<0.001). The higher the BMI, the less was the increase of serum anti-D. Mean peak levels 72 hours after injection was 89 ng per mL in lean women, but estimated levels were 28 to 60 percent lower in women with a BMI of 28 to 40 kg per m2. The effect of a BMI higher than 27 kg per m2 on anti-D was not gradual but progressive. Similarly, the BMI affected serum concentrations of anti-D subclasses IgG1-4 (p<0.001).

CONCLUSION

The BMI needs consideration for the adjustment of the dosage of anti-D, provided its bioavailability to suppress alloimmunization is reflected by measurable amounts in the serum.