The statement that the placenta produces its own gonadotropin, estrogen, progesteron and corticoid, has been generally accepted. Recently prolactin, ACTH and TSH-like hormone productions have also been attributed to it, but the existence of somatotropic hormone (=STH), a hormone that has come into attention only very recently, in the placenta has been suspected but not yet definitively demonstrated.
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Mineko Fukushima (1961) studied this question.