Purpose of investigation: Successful pregnancy depends on the ability of the mother’s immune system to undergo a process of immunoregulation in order to tolerate the fetus, and also to create and sustain a nurturing environment during all the stages of pregnancy. Several reports point to interleukin 10 (IL-10) as being vital for normal pregnancy, and low IL-10 levels as being associated with pregnancy complications. This study aimed to compare IL-10 levels in normal and complicated pregnancy conditions. Material and Methods: The authors compared levels of IL-10 produced upon stimulation of maternal peripheral blood mononuclear cells (PBMC) from women at different stages of normal gestation with those produced by women with pregnancy complications, such as recurrent spontaneous miscarriage (RSM), preterm delivery (PTD), premature rupture of fetal membranes (PROM), pre-eclampsia, and intrauterine fetal growth retardation (IUGR). Results: Median levels of IL-10 are statistically significantly lower in pathological conditions as compared to matching gestational ages of normal pregnancy. Conclusion: Healthy pregnancy is associated with higher levels of IL-10, while pathologic pregnancies are associated with lower levels of IL-10.