Two representations of affected status in the same pedigree with recurrent spontaneous preterm birth. Numbers indicate the gestational ages for each individual, in weeks. Circles indicate females and squares indicate males, diamonds indicate miscarriages. Preterm birth is indicated with closed (black) circles or squares, and question marks indicate unknown gestational ages. (a) Illustration of the pattern of affected status if the infant is proband for preterm birth. (b) Illustration of the pattern of affected status if the mother is proband for preterm birth. Modeling the incidence of maternal and infant phenotypes indicates that genetic influences on the timing of parturition are important and complex, and thus unlikely to be explained by a single gene model. Reproduced from  with permission from S Karger AG, Basel.