['Cell-mediated immunosuppression due to interleukin (IL)-10 may contribute to normal pregnancy. By contrast, delivery is associated with a predominance of T-helper-1 (Th1) cytokines (IL-12, interferon-gamma) and might be regarded as a graft rejection process. The aim of the study was to assess IL-10 and IL-12 levels in cord blood samples from newborns and their normal mothers in relation to the gestational age and type of delivery. Cord blood and serum samples were obtained from 31 term newborns (gestational age 38-42 weeks) and 40 preterm newborns (mean gestational age 32 weeks). Serum samples were obtained from 26 mothers of term newborns at birth. There were 18 term and preterm infants born by caesarean section. Measurements of IL-10 and IL-12 levels by ELISA were repeated in mothers 15 days after delivery and in 11 preterm infants (median 14 days of age). Cord blood IL-10 levels were significantly higher in preterm than in term newborns (median 17.0 versus 3.2 pg/ml, P = 0.0001), but were similar to term newborns and paired mothers (2.2 versus 1.0 pg/ml). Term and preterm newborns also showed similar cord blood IL-12 levels (median 349 versus 320 pg/ml), and these levels were significantly higher when compared to their paired mothers (median 14.5 pg/ml, P = 0.0003). Cord blood IL-10 levels showed a significant inverse correlation with gestational age (P = 0.0001). When preterm infants, at several weeks post-delivery, were compared to gestational age matched newborns, their IL-10 levels were similar (median 8.3 pg/ml) whereas IL-12 levels were clearly lower (147 pg/ml; P = 0.0007). The type of delivery (vaginal versus caesarean) did not influence cord blood IL-10 and IL-12 results.'] Are cord blood interleukin-10 levels increased in preterm newborns?