Figure 1.

For the purpose of examining various types of placentas consistently, we designed the data extraction forms that could be used in all types of placentation for singleton and multiple gestations. This system considered four elements: (1) umbilical cord(s), (2) placental disc(s), (3) chorioamniotic sac(s) (placental membranes), and (4) dividing membrane(s). The number of umbilical cords was used as a marker for the number of fetuses present in a gestation. In singleton pregnancies, the cord, disc, and sac were all identified as “A.” In multifetal pregnancies, when the delivery personnel marked the cords, the cord ID for the firstborn was designated as “A,” for the second-born as “B,” and so on. If birth order was unknown, cords were arbitrarily designated using the letters M, N, and so on. Identifiers for placental membranes (sacs) were designated with one or more letters (e.g., A, B, AB; M, N, MN) depending on the placentation. Dividing membranes were indicated with two letters (e.g., AB; MN) and placental discs were each indicated with a single letter when discs were distinct and two (or more) letters when fused (with or without a dividing membrane, depending on the number of sacs). Forms for tissue samples and the microscopic examination used the cord ID. For a fused disc, if a dividing membrane could not be observed, an imaginary perpendicular midway between the umbilical cord insertion points was used to distinguish “side A” and “side B” for purposes of sampling and performing the microscopic examination.