PROBLEM: There is an increased doubt about the identity of isolated cytotrophoblast cells at term. Therefore, we compared pregnancy serum levels of three hormones [human placental lactogen (hPL), human chorionic gonadotropin (hCG), and leptin] with the capacity for hormone production of early placentae [EP; 8-13 weeks of gestation (WG)] and term placentae (TP; 38-42 WG). METHODS: Serum levels of these hormones were determined in 15 paired maternal (7-41 WG) and fetal (37-41 WG) samples. Cytotrophoblast cells were isolated from term (TP; 38-42 weeks) and early (EP; 8-13 weeks) placentae by enzymatic digestion and subsequent purification on a Percoll gradient. These cells were cultured for 6 days. The production of the hormones hPL, hCG, and leptin was determined as release during culture + cell content after culture - cell content before culture. RESULTS: Serum levels (mean +/- SD; n = 15) at 7-12 and 37-41 WG were 89,652 +/- 21,431 and 13,620 +/- 5854 mIU/ml for hCG, 400 +/- 182 and 7088 +/- 2030 ng/ml for hPL, and 12,675 +/- 4266 and 32,236 +/- 10,961 pg/ml for leptin, respectively. For cultured cells from EP and TP, hCG and hPL showed different patterns of release during the first 2-3 days. While the release of these two hormones by EP cytotrophoblast cells continued during 6 days in culture, their concentrations reached a plateau for TP cytotrophoblasts between 4 and 6 days. Leptin was undetectable (< 15 pg/ml) in TP cell cultured media, while for EP all three hormones showed the same release profiles. Production calculated for 30,000 TP trophoblast cells cultured for 6 days (n = 8) was 2-31 mIU for hCG and 0.5-2 ng for hPL. For EP (n = 11), it was 50-1070 mIU for hCG, 15-323 ng for hPL, and 137-580 pg for leptin. Net synthesis of hCG and hPL for TP was > 10-fold and < 1-fold, respectively. In contrast, the production of all three hormones for EP was at least 100 times the initial cell content. CONCLUSIONS: These results demonstrate that trophoblasts from early pregnancy show much higher production rates of hCG, hPL, and leptin than at term. However, the in vitro findings are difficult to be reconciled with the different serum concentrations of the two hormones hPL and leptin observed during the course of pregnancy.