Average methylation of all samples for first, second and third trimester. Methylation Index (MI) was calculated for each sample by calculating the mean of all analysable Infinium β-values (26, 162 probes) for that sample. The MIs were then grouped by gestation and shown as box and whisker plots. First and second trimester placentas show a similar overall level of methylation (p = 0.46) with median MIs of 0.238 and 0.241, respectively. Third trimester samples show significantly elevated average MI values (median = 0.256) relative to both first and second trimester, indicating that there is a significant increase in methylation level from second to third trimester.
Novakovic et al. BMC Genomics 2011 12:529 doi:10.1186/1471-2164-12-529