FIGURE 3.

The combination of maternal vitamin D concentrations pre- and postsupplement is a determinant of cluster membership. Maternal pre- and postsupplement vitamin D concentrations were encoded as “low” (<30 ng/mL) or “high” (≥30 ng/mL), forming the basis for a combined variable describing the intrauterine exposure at both times (e.g., low-low means that both pre- and postsupplement concentrations of vitamin D were <30 ng/mL). This combined variable was a strong determinant of the child’s cluster membership (χ² P = 0.03). An overrepresentation of low-low and underrepresentation of high-high is observed in cluster 1, suggesting that the presupplement concentrations combined with postsupplement concentrations play a role for cluster segregation. Total sample N = 245: group 1, 46; group 2, 94; and group 3, 105.