OBJECTIVE: To identify factors influencing the number of fetal cells in maternal blood.

METHODS: A total of 57 pregnant women at a gestational age of weeks 11-14 were included. The number of fetal cells in maternal blood was assessed in 30 ml of blood using specific markers for both enrichment and subsequent identification.

RESULTS: Participants carrying male fetuses had a higher median number of fetal cells in maternal blood than those carrying female fetuses (5 vs. 3, p = 0.04). Certain cytokines (RANTES, IL-2 and IL-5) were significantly associated with the number of fetal cells in maternal blood.

CONCLUSION: The number of fetal cells in maternal blood is associated with certain cytokines and fetal gender.