Relationship between interbirth interval and ASD recurrence risk by sex and family type. Recurrence risk to subsequent children decreases with increasing interval between births. (A), (B), and (C) show the logistic regression estimated recurrence risk by the number of months since the birth of the second affected child within each subgroup of individuals as indicated by colors (blue for males, red for females) and solid (female-containing (FC) families) and dashed (male-only (MO) families) lines. P values from the whole-model test of logistic regression for affection status given the natural log of interbirth interval (months) are noted; fractions show the number of affected individuals out of the total within the indicated subgroup. (D, E) show the interbirth interval for all evaluated children given their affection status and either their sex (D) or family type (E).