The "exposome" is defined as 'the totality of human environmental exposures from conception onwards, complementing the genome' and its holistic approach may advance understanding of disease aetiology. We aimed to describe the correlation structure of the exposome during pregnancy to better understand the relationships between and within families of exposure and to develop analytical tools appropriate to exposome data. Estimates on 89 environmental exposures of current health concern were obtained for 728 women enrolled in The INMA (INfancia y Medio Ambiente) birth cohort, in Sabadell, Spain, using biomonitoring, geospatial modeling, remote sensors and questionnaires. Pair-wise Pearson's and polychoric correlations were calculated and principal components were calculated. The median absolute correlation across all exposures was 0.06 (5th - 95th centiles: 0.01 - 0.52). There were strong levels of correlation within families of exposure (median = 0.40, 5th - 95th centiles: 0.04 - 0.81). Nine exposures (10%) had a correlation higher than 0.5 with at least one exposure outside their exposure family. Effectively all the variance in the dataset (99.5%) was explained by 43 principal components. Future exposome studies should interpret exposure effects in light of their correlations to other exposures. The weak to moderate correlation observed between exposure families will permit adjustment for confounding in future exposome studies.