OBJECTIVETo develop a nested polymerase chain reaction (PCR) technique for fetal SRY gene identification using cell-free fetal DNA in maternal plasma.

METHODSPeripheral blood samples were obtained from 30 pregnant women and cell-free DNA was extracted by the phenol/chloroform method from plasma. The nested PCR was carried out to amplify the fragment of SRY gene by two sets of PCR primer pairs. Direct sequencing analysis was then performed on the PCR product.

RESULTSAmong the 17 women bearing male fetuses, SRY sequences were detected in 15 plasma samples after nested PCR amplification, while none of the 13 women bearing female fetuses had the positive results. The accuracy and sensitivity were 93.3% (28/30) and 88.2% (15/17), respectively.

CONCLUSIONThe phenol/chloroform extraction for fetal DNA in maternal plasma was effective and simple. And the nested PCR amplification of SRY sequence is a convenient and low-cost approach for the non-invasive early prenatal diagnosis of sex-linked inheritant diseases.