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A growing body of evidence suggests that the malnourished fetus may develop peripheral insulin resistance1 and that low birth weight is a risk factor for metabolic and cardiovascular disease in adulthood.2,3 As intrauterine nutrition and fetal growth depends on the placenta, we hypothesise that low weight placenta may be linked to the increase in serum insulin concentration in small for gestational age (SGA) term newborn infants.
We compared 20 SGA babies with 40 of appropriate size for gestational age (AGA) in a cross sectional study matched by mother’s age, weight before pregnancy, weight increase throughout pregnancy, and duration of gestation. Risk factors related to retardation of fetal growth and conditions that affect glucose metabolism during labour were exclusion criteria. Gestational age ⩾38 and <41 weeks, birth weight <10th centile, serum insulin concentration ⩾30 pmol/l, and weight of placenta <400 g defined term babies, SGA, high serum insulin concentration, and low weight placenta.
Babies born SGA with low weight placenta (346 (19) g) had the lowest birth weight (2056 (269) g) and the highest serum insulin concentration (51.9 (10.8) pmol/l), whereas babies born SGA with placental weight >400 g (466 (65) g) had the lowest serum insulin concentration (15.9 (3.3) pmol/l) (values are mean (SD)). On the other hand, babies born AGA exhibited the highest birth weight (3362 (234) g) and placental weight (549 (82) g), with mean serum insulin concentration of 30.9 (8.6) pmol/l. Glucose concentrations were similar between the groups, and there were no hypoglycaemic events. Placental weight and serum insulin concentration showed a significant inverse correlation (fig 1).
Multivariate regression analysis of the relation between low weight placenta and high serum insulin concentration found an odds ratio of 2.1, 95% confidence interval 1.3 to14.3, p = 0.01.
Although serum insulin concentrations are lower in lower birth weight babies,4 in this study SGA infants with low weight placenta had the lowest birth weight but the highest serum insulin concentration, which suggests that these babies may have developed insulin resistance in utero, a phenomenon that seems to be linked to the low weight placenta. Whether the low weight placenta causes immaturity of the placenta and/or placental dysfunction and this affects the somatotropic axis in SGA children remains to be established.
This work was supported by grants from the National Science and Technology Council of Mexico (SIVILLA 20020402012) and the Research Promotion Fund of the Mexican Social Security Institute (FP 2002/369).
Competing interests: none declared