The scientists determined this by using lasers to map the growth rings in baby teeth generated during different developmental periods. The researchers observed higher levels of lead in children with autism throughout development, with the greatest disparity observed during the period following birth. Children with autism had lower zinc levels earlier in the womb, but these levels then increased after birth, compared to children without autism. “With baby teeth, we can actually do that.”Patterns of metal uptake were compared using teeth from 32 pairs of twins and 12 individual twins. The team previously showed that the amount of lead in different layers of dentine corresponds to lead exposure during different developmental periods.