Fetal sex prediction can be achieved using PCR targeted at the SRY gene by 
analysing cell-free fetal DNA in maternal serum. Unfortunately, the results 
reported to date show a lack of sensitivity, especially during the first 
trimester of pregnancy. Therefore, determination of fetal sex by maternal serum 
analysis could not replace karyotype analysis following chorionic villus 
sampling. A new highly sensitive real-time PCR was developed to detect an SRY 
gene sequence in maternal serum. Analysis was performed on 121 pregnant women 
during the first trimester of pregnancy (mean gestational age: 11.8 weeks). 
Among them, 51 had at least one previous male-bearing pregnancy. Results were 
compared with fetal sex. SRY PCR analysis of maternal serum was in complete 
concordance with fetal sex. Among the 121 pregnant women, 61 were bearing a male 
fetus and 60 a female fetus. No false-negative results were observed. 
Furthermore, no false-positive results occurred, even though 27 women carrying a 
female fetus during the current pregnancy had at least one previous male-bearing 
pregnancy. This study demonstrates that a reliable, non-invasive sex 
determination can be achieved by PCR analysis of maternal serum during the first 
trimester of pregnancy. This non-invasive approach for fetal sex prediction 
should have great implications in the management of pregnant women who are 
carriers of an X-linked genetic disorder. Prenatal diagnosis might thus be 
performed for male fetuses only, avoiding invasive procedures and the risk of 
the loss of female fetuses.