EFFECTS OF GESTATIONAL-AGE, MATERNAL DIABETES, AND INTRAUTERINE GROWTH-RETARDATION ON MARKERS OF FETAL BONE TURNOVER IN AMNIOTIC-FLUID

Little is known about the dynamics of bone formation and bone resorpti on in utero, particularly the normal changes that occur throughout ges tation and in clinical situations that result in low bone mass at birt h. The objectives of this study were to describe the effects of gestat ional age on markers of fetal bone turnover, and to investigate whethe r the reported low bone mass at birth in small-for-gestational-age (SG A) infants and infants of diabetic mothers (IDMs) was associated with biochemical markers of decreased bone formation or increased bone reso rption in utero. Bone formation and resorption were assessed by measur ement of carboxyterminal propeptide of type I procollagen (PICP) and c ross-linked carboxyterminal telopeptide of type I collagen (ICTP), res pectively, in 201 amniotic fluid samples. These markers are by-product s of type I collagen formation and degradation, respectively, and have been used in the assessment of bone metabolism ex utero. Both PICP an d ICTP concentrations in amniotic fluid were inversely associated with gestational age (P < 0.0001). Amniotic fluid concentrations of PICP i ncreased exponentially in relation to infant birthweight (P = 0.008), and SGA infants had lower amniotic fluid PICP concentrations than cont rols (P = 0.07). The presence of diabetes in the mother was not associ ated with alterations in amniotic fluid PICP or ICTP concentrations. A lthough maturational effects on clearance of bone markers from amnioti c fluid cannot be excluded, these data are consistent with a high turn over of bone matrix early in fetal life, and a reduction in bone forma tion when fetal growth is compromised.