Recently we reported that second‐trimester amniotic fluid (AF) is an abundant source of fetal mesenchymal stem cells (MSCs). In this study, we analyze the origin of these MSCs and the presence of MSCs in human‐term AF. In addition, different parts of the human placenta were studied for the presence of either fetal or maternal MSCs. We compared the phenotype and growth characteristics of MSCs derived from AF and placenta.

Cells from human second‐trimester (mean gestational age, 19⁺² [standard deviation, ± 1⁺³] weeks, n = 10) and term third‐trimester (mean gestational age, 38⁺⁴ [standard deviation, ± 1] weeks, n = 10) AF, amnion, decidua basalis, and decidua parietalis were cultured in M199 medium supplemented with 10% fetal calf serum and endothelial cell growth factor. Cultured cells were immunophenotypically characterized, the adipogenic and osteogenic differentiation capacity was tested, and the growth kinetics were analyzed. The origin of fetal and maternal cells was determined by molecular human leukocyte antigen typing.

We successfully isolated MSCs from second‐trimester AF, amnion, and decidua basalis as well as term amnion, decidua parietalis, and decidua basalis. In contrast, MSCs were cultured from only 2 out of 10 term AF samples. The phenotype of MSCs cultured from different fetal and maternal parts of the placenta was comparable. Maternal MSCs from second‐trimester and term decidua basalis and parietalis showed a significantly higher expansion capacity than that of MSCs from adult bone marrow (p < .05).

Our results indicate that both fetal and maternal MSCs can be isolated from the human placenta. Amnion is a novel source of fetal MSCs, likely contributing to the presence of MSCs in AF. Decidua basalis and decidua parietalis are sources for maternal MSCs. The expansion potency from both fetal and maternal placenta‐derived MSCs was higher compared with adult bone marrow–derived MSCs.