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Second trimester chorionic villi of normal (19 weeks of amenorrhea: wa) and trisomy 21 (18 wa) placentae. In normal placenta, a large amount of cytotrophoblastic cells (CT) have fused into a thin multinucleated syncytiotrophoblast (ST). In trisomy 21 placenta, many cuboidal cytotrophoblastic cells (CT) are still present beneath the syncytiotrophoblast (ST) increasing the thickness of the trophoblastic layer. Scale bar = 10 μm.
