Fetal RHD genotyping in maternal plasma at 11-13 weeks of gestation

Area of Science:

• Maternal-fetal medicine
• Genetics
• Molecular diagnostics

Background:

• RhD hemolytic disease of the newborn (HDN) is a significant concern.
• Accurate fetal RhD status determination is crucial for managing RhD-negative pregnancies.
• Current methods for fetal RhD genotyping can be invasive or performed later in gestation.

Purpose of the Study:

• To assess the feasibility of fetal RHD genotyping using cell-free fetal DNA (ccffDNA) at 11-13 weeks gestation.
• To evaluate a high-throughput robotic technique for this purpose.
• To determine the accuracy of non-invasive fetal RHD genotyping.

Main Methods:

• Circulating cell-free fetal DNA (ccffDNA) was extracted from 0.5 ml plasma of 591 RhD-negative pregnant women using a robotic technique.
• Real-time quantitative polymerase chain reaction (PCR) targeting RHD gene exons 5 and 7 was employed for fetal RHD genotyping.
• Fetal RHD genotype results were compared with neonatal RhD phenotype for validation.

Main Results:

• Conclusive results were obtained in 85.7% (502/591) of cases, with inconclusive results in 14.3% (84/591).
• The positive predictive value for RhD-positive fetuses was 100% (95% CI 96.8-100).
• The negative predictive value for RhD-positive fetuses was 96.5% (95% CI 93.7-99.2).

Conclusions:

• Non-invasive fetal RHD genotyping is feasible at 11-13 weeks gestation.
• The high-throughput robotic technique provides accurate fetal RHD status determination.
• This method offers a reliable approach for early identification of RhD status in RhD-negative pregnancies.