Maternal serum adiponectin and infant birthweight: the role of adiponectin isoform distribution

Adiponectin is an insulin-sensitizing protein that circulates in oligomeric complexes, including trimers, hexamers and high-molecular-weight (HMW) multimers. In pregnant women, conflicting associations have been reported between maternal serum levels of total adiponectin (i.e. reflecting all isoforms) and infant birthweight. As the HMW complex has recently been proposed as the primary mediator of metabolic bioactivity, we hypothesized that differences in isoform distribution may underlie these conflicting reports. Therefore, we evaluated the relationship between maternal adiponectin isoforms and infant birthweight.

HMW and total adiponectin, as well as the ratio of HMW to total adiponectin (ratio known as S(A)), were measured in healthy pregnant Caucasian women (n = 58) undergoing an oral glucose tolerance test (OGTT), following an abnormal glucose challenge test.

On univariate analysis adjusted for neonate gender and length of gestation, birthweight was positively correlated with weight gain in pregnancy (r = 0.29, P = 0.031) and inversely associated with the IS(OGTT) index of insulin sensitivity (r = -0.27, P = 0.041), total adiponectin (r = -0.31, P = 0.021), HMW adiponectin (r = -0.34, P = 0.0093) and S(A) (r = -0.34, P = 0.011). On multiple linear regression analyses, however, total adiponectin was not related to birthweight. By contrast, HMW adiponectin was related at borderline significance (t = -1.87, P = 0.068), while S(A) emerged as an independent negative determinant of infant birthweight (t = -2.46, P = 0.0175). Adjusted mean neonatal birthweight was significantly higher in the infants of women comprising the lowest tertile of S(A) compared to women in the highest tertile of S(A) (3684 vs. 3424 g, P = 0.0375).

The proportion of maternal serum adiponectin in HMW form (S(A)) is independently and inversely associated with infant birthweight. Thus, adiponectin isoform distribution, rather than total adiponectin concentration, may be a correlate of foetal size.