Type I collagen markers in cord serum of appropriate vs. small for gestational age infants born during the second half of pregnancy

Background The serum concentration of the N-terminal propeptide of type I p rocollagen (PINP) reflects the synthesis rate of type I collagen, whereas t he corresponding C-terminal telopeptide (ICTP) mirrors its degradation. Design PINP and ICTP were measured in a total of 690 cord serum samples fro m 592 appropriate-for-gestational-age (AGA) infants and 98 smal-for-gestati onal-age (SGA) infants. These markers were compared between AGA and SGA inf ants of different gestational ages, ranging from 23 to 41 weeks, and birth weights, from 620 to 4555 g. Results Both PINP and ICTP levels were very high in the preterm AGA infants and declined significantly with advancing gestational age, paralleling the shape of the fetal growth velocity curve. Regardless of the quite large in terindividual variations observed in these markers, PINP was significantly lower in both the preterm and term AGA infants than in the SGA infants. Thi s was also the case for ICTP in the preterm infants of gestational age less than 36 weeks. In stepwise multiple regression analyses, gestational age, being either AGA or SGA and head circumference were significant factors to explain the levels of PINP and ICTP. The levels of PINP and ICTP were corre lated with each other highly significantly in both the AGA and SGA infants (r(s) = 0.700 and 0.692, respectively; P < 0.001 in both). Conclusions The levels of type I collagen markers seem to follow closely th e shape of the fetal growth velocity curve during different stages of gesta tion. However, because of the large interindividual variations observed, fu rther studies are needed before the significance of these markers for the a ssessment of normal and abnormal fetal growth can be established.