Inverse correlation between maternal weight and second trimester circulating cell-free fetal DNA levels

OBJECTIVE: Clinical applications of the analysis of cell-free fetal DNA in maternal plasma and serum are expanding. However, use of fetal DNA during prenatal screening requires knowledge of variables that might affect its levels in the maternal circulation. We conducted this study to estimate the effect of selected demographic factors on fetal DNA levels in the first and second trimesters of pregnancy. METHODS: We developed a database that included fetal DNA levels and clinical information, such as maternal age, ethnicity, weight, and smoking history. We measured fetal DNA levels in maternal plasma and serum using real-time quantitative polymerase chain reaction amplification of a Y chromosome specific sequence. The fetal DNA data from fresh first trimester plasma and previously frozen second trimester serum samples were analyzed separately. Fetal DNA levels were adjusted according to gestational age and storage time and then analyzed in association with the demographic factors. RESULTS: In the first trimester group, no significant association between maternal age, weight, ethnic background, or smoking and plasma fetal DNA levels was observed. In the second trimester group, a significant inverse correlation between maternal weight and serum fetal DNA level was demonstrated (r = -0.26, P = .007). This was especially prominent when the mothers weighed more than 170 lb (P = .001). Maternal age, ethnicity, and smoking were not significantly associated with the second trimester serum fetal DNA levels. CONCLUSION: Fetal DNA levels are affected by maternal weight in the second trimester. A correction for this effect may be needed in larger-scale studies or for future clinical applications that measure cell-free fetal nucleic acids in maternal circulation.