C4A and polycystic ovary syndrome: We measured plasma levels of complement pathway proteins by Slow Off-rate Modified Aptamer (SOMA)-scan plasma protein measurement for the classical (C4, C4a, and C4b) and alternative pathways (C3, C3b, iC3b, properdin, and factors B, D, and H) in weight and age-matched non-obese non-insulin resistant women with PCOS (n = 24) and control women (n = 24).