OBJECTIVES: The study aims were to conclusively demonstrate apoptosis
in the human placenta and to quantify its incidence at different stage
s of pregnancy. STUDY DESIGN: Placental samples were obtained from 28
first-trimester pregnancies and 38 uncomplicated third-trimester pregn
ancies. Light microscopy, electron microscopy, and terminal deoxynucle
otidyl transferase-mediated deoxyuridine triphosphate marker nick end-
labeling staining were used to identify apoptosis. Light microscopy wa
s used to quantify its incidence. RESULTS: Apoptosis has been conclusi
vely demonstrated within placental tissue. Quantification of apoptosis
(medians and interquartile ranges) was as follows: first trimester (n
= 28), 0.07% of cells (0.05% to 0.14%); third trimester (n = 39), 0.1
4% of cells (0.09% to 0.20%). The incidence of apoptosis was significa
ntly higher in the third trimester than in the first trimester (p < 0.
01, Mann-Whitney U test). CONCLUSIONS: Placental apoptosis increases s
ignificantly as pregnancy progresses, suggesting that it may play a ro
le in the normal development and aging of the placenta.