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RETARDED EMBRYONIC DEVELOPMENT AND PREGNANCY TERMINATION IN OVARIECTOMIZED GUINEA-PIGS: PROGESTERONE DEFICIENCY AND DECIDUAL COLLAPSE

Summary.: Progesterone deficiency in the pregnant guinea-pig, ovariectomized before implantation, retards growth of the conceptuses and embryos and terminates pregnancy on or before Day 16.

In a fresh investigation, conceptuses from ovariectomized, 12- to 16day pregnant females were examined in serial sections, and from Day 12 a conspicuous degeneration of part of the decidua occurred, interfering with the normal development of the adjacent placenta. This degeneration undoubtedly contributed to the retardation of the conceptus during the following days, when very active embryonic differentiation was normally taking place. It was the total collapse of the decidua with massive haemorrhage, almost always on Day 16, which abolished surviving pregnancies. Similarly in the unmated guinea-pig, the traumatic deciduoma breaks down at the end of the 16-day cycle, when the corpora lutea regress before the next oestrus.

Decidual degeneration could be prevented in ovariectomized females if progesterone was given sufficiently early in pregnancy. In other developing conceptuses, however, in which progesterone had been deferred till later, an area of decidual degeneration, no longer in contact with the placenta, could persist for some days.

The rôle of the decidua in early pregnancy is discussed.