BACKGROUND: Obtaining fetal DNA or RNA by either chorionic villus sampling (CVS) 
or amniocentesis is currently, the gold standard prenatal diagnosis. However, 
these invasive procedures carry risk of miscarriage. A reliable method for 
non-invasive prenatal diagnosis (NIPD) has long been sought to reduce the risk 
of miscarriage.
METHODS: Cell-free fetal RNA was extracted from the plasma of peripheral blood 
from 121 women 9-20 weeks of pregnancy. Five single nucleotide polymorphism 
(SNP) loci in PLAC4 gene were analyzed by reverse transcriptase multiplex 
ligation-dependent probe amplification (RT-MLPA), followed by capillary 
electrophoresis. Karyotype analysis was used for confirmation of prenatal 
diagnosis of trisomy 21.
RESULTS: Of 121 samples, 23 were diagnosed with trisomy 21, 87 with normal 
ploidy, nine had all five SNP loci homozygous and two had one heterozygous SNP 
locus. Comparing with karyotype analysis, the diagnostic sensitivity and 
specificity of RT-MLPA were 92% and 100%, respectively.
CONCLUSIONS: RT-MLPA is a convenient and reliable method for the diagnosis of 
trisomy 21. We have shown that this method has good specificity, high 
sensitivity, and high throughput, making this technique applicable for NIPD in 
clinical practice.