Influence of gestational age on fetal deoxyribonucleic acid retrieval in maternal peripheral blood

OBJECTIVE: We wanted to verify whether gestational age influences the retrieval of fetal deoxyribonucleic acid in maternal blood to identify the best period for maternal blood sampling for a future noninvasive prenatal diagnoses. STUDY DESIGN: We amplified 81 deoxyribonucleic acid samples extracted from the peripheral blood of 27 pregnant women (18 bearing male fetuses and 9 bearing females) by nested polymerase chain reaction of the Y-specific sequence DYS14. We obtained three blood samples (one per gestational trimester) from each woman. Statistical evaluation was assessed by the McNemar test of symmetry. RESULTS: Polymerase chain reaction results in male-bearing pregnancies differed significantly between the first and second trimesters and between the second and third trimesters (p < 0.025) in parallel with a decrease in sensitivity in the second trimester (67%) compared with the first (94%) and third trimesters (100%). CONCLUSIONS: The drop in sensitivity from the first to the second trimester witnesses a variable concentration of fetal cells in maternal blood, with a negative balance in the second trimester. Therefore, to achieve an adequate polymerase chain reaction accuracy, the choice of gestational age is relevant and the first trimester seems to be more suitable than the second trimester.(Am J Obstet Gynecol 1997;177:22)