Synchronous Viiious Immaturity

The term synchronous is used for histologic features of immature viiious trees that correspond to what we expect to be normal for the respective stage of pregnancy (Schweikhart et ai., 1986). For a normal baseline, we refer to the pictures and data provided by Boyd and Hamilton (1970), Kaufmann (1981), Vogel (1986), Stoz et ai. (1988), and Vogel (1996), and to the data presented in Chapter 8.

From the 8th to 24th week p. m., the immature villous trees are composed of uniformly thick, bulbous, immature intermediate villi (villous maturation score 00). Until week 28 these are completed by some newly formed mature intermediate villi (score 01). The trophoblastic surface of the immature intermediate villi is unevenly curved and distended (Fig. 15.8A). Terminal villi are virtually absent. The numerous side branches of small caliber are composed of real sprouts and newly produced mesenchymal villi. For geometrical reasons, the chance of obtaining flat sections depends on the villous diameter and decreases with increasing villous caliber. Therefore, the rare event of tangential sectioning of such immature cases with prevailing large villi does not give an incorrect impression of sprouting (Fig. 15.8B).

In later stages of villous development (weeks 29-36; villous maturation scores 10-12), increasing amounts of mature intermediate villi are formed. In particular, in weeks 32 to 34, when these villi clearly dominate the histologic section, they are characterized by rather large, homogeneous calibers (150-250 pm) and a highly cellular stroma (Fig. 15.9; also see Fig. 8.9). The number of terminal villi slowly increases throughout this period. By definition, placentas showing synchronous villous immaturity can be found only in cases of premature deliveries. On the other hand, as discussed in Chapter 14, in only 33% of premature deliveries are the placentas in fact structurally immature (Schweikhart et al., 1986); rather, most prematurely delivered cases are characterized by fully mature or even “hypermature” features. Becker and Rockelein (1989) suggested this to be responsible for preterm onset of labor. This, however, still remains speculative.

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