The relationship between S isoform concentration and BW-PW correlation. The term BW-PW correlation expresses the correlation between birth weight and placental weight. ACP1 is the acid phosphatase locus 1. A, B, C, BA, CA, CB are the ACP1 phenotypes. In abscissa S isoform concentrations of each ACP1 phenotype are also reported. The rank correlation coefficient according to Spearman (27) between BW-PW correlation and S isoform concentration is rs = 0.3, p not significant.