Obesity may reduce anti-D efficacy in pregnancy: review


By Siobhan Calafiore

10 Jul 2024

Obesity may reduce anti-D immunoglobulin prophylaxis efficacy for the protection of alloimmunisation in women during pregnancy, increasing the risk of haemolytic disease of the foetus and newborn, an Australian review suggests.

Researchers conducted a systematic review of 10 studies, of which three were suitable for meta-analysis, involving Rh(D)-negative pregnant women carrying a Rh(D)-positive foetus. All patients received anti-D RhIg prophylaxis at dosages 1250-1500 IU during the gestational period between weeks 28 and 32.

A high BMI exhibited an overall significant reduction in serial anti-D levels, signifying potential implications for prophylaxis efficacy, the researchers said.

Findings published in Vox Sanguinis [link here] showed high BMI/weight had lower odds of serial anti-D level exceeding 30 ng/mL (arcsine risk difference [ARD] = 0.376). The meta-analysis of correlation coefficients also presented a significant negative correlation (r = 0.59) between high BMI/weight and serial anti-D levels.

Heterogeneity among the studies was considered low.

All papers raised concerns about anti-D immunoglobulin sufficiency at term, with some patients reporting undetectable anti-D following administration at week 28.

“[The findings suggest] that obese individuals may be at a higher risk of inadequate anti-D prophylaxis levels and response, which potentially causes the increased risk of haemolytic disease of the newborn or transfusion reactions,” the authors wrote.

“Therefore, healthcare providers may need to consider adjusting the anti-D prophylaxis dosage based on a patient’s BMI or weight. Obese patients may thus require a higher dose to achieve the same protective effect as individuals with normal BMI/weight.

“In obese individuals, the process of absorption at the injection site may exhibit delays. This delay could potentially be attributed to factors such as inadequate needle penetration into the more vascularised muscular tissue, which contributes to a prolonged residence of immunoglobulins within the adipose tissue.

“Furthermore, it is pertinent to contemplate the fact that a notable percentage of obese individuals often partake in fewer physical activities in comparison with their non-obese counterparts. This diminished level of physical activity could potentially be a leading factor to the observed deceleration in absorption kinetics at the injection site.”

The researchers advised clinicians to effectively communicate with patients regarding the potential impact of obesity on anti-D antibody levels.

“While patient understanding and adherence to treatment regimens are critical for achieving optimal outcomes, health intervention measures such as addressing obesity through lifestyle modification and weight management strategies are crucial long-term conditions that could ultimately rectify overall health outcomes.”

They said updating clinical guidelines and conducting risk assessments based on the negative correlation between BMI/weight and anti-D serum levels could help improve safe and effective patient care, but also noted caution was warranted due to study limitations such as variability in study design and confounding factors.

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