Gérard Bréart

BACKGROUND: Existing fetal growth references all suffer from 1 or more major methodologic problems, including errors in reported gestational age, biologically implausible birth weight for gestational age, insufficient sample sizes at low gestational age, single-hospital or other non-population-based samples, and inadequate statistical modeling techniques. METHODS: We used the newly developed Canadian national linked file of singleton births and infant deaths for births between 1994 and 1996, for which gestational age is largely based on early ultrasound estimates. Assuming a normal distribution for birth weight at each gestational age, we used the expectation-maximization algorithm to exclude infants with gestational ages that were more consistent with 40-week births than with the observed gestational age. Distributions of birth weight at the corrected gestational ages were then statistically smoothed. RESULTS: The resulting male and female curves provide smooth and biologically plausible means, standard deviations, and percentile cutoffs for defining small- and large-for-gestational-age births. Large-for-gestational age cutoffs (90th percentile) at low gestational ages are considerably lower than those of existing references, whereas small-for-gestational-age cutoffs (10th percentile) postterm are higher. For example, compared with the current World Health Organization reference from California (Williams et al, 1982) and a recently proposed US national reference (Alexander et al, 1996), the 90th percentiles for singleton males at 30 weeks are 1837 versus 2159 and 2710 g. The corresponding 10th percentiles at 42 weeks are 3233 versus 3086 and 2998 g. CONCLUSIONS: This new sex-specific, population-based reference should improve clinical assessment of growth in individual newborns, population-based surveillance of geographic and temporal trends in birth weight for gestational age, and evaluation of clinical or public health interventions to enhance fetal growth. fetal growth, birth weight, gestational age, preterm birth, postterm birth.

Increased bone turnover has been suggested as a potential risk factor for osteoporotic fractures. We investigated this hypothesis in a prospective cohort study performed on 7598 healthy women more than 75 years of age. One hundred and twenty-six women (mean years 82.5) who sustained a hip fracture during a mean 22-month follow-up were age-matched with three controls who did not fracture. Baseline samples were collected prior to fracture for the measurement of two markers of bone formation and three urinary markers of bone resorption: type I collagen cross-linked N- (NTX) or C-telopeptide (CTX) and free deoxypyridinoline (free D-Pyr). Elderly women had increased bone formation and resorption compared with healthy premenopausal women. Urinary excretion of CTX and free D-Pyr, but not other markers, was higher in patients with hip fracture than in age-matched controls (p = 0.02 and 0.005, respectively). CTX and free D-Pyr excretion above the upper limit of the premenopausal range was associated with an increased hip fracture risk with an odds ratio (95% confidence interval) of 2.2 (1.3-3.6) and 1.9 (1.1-3.2), respectively, while markers of formation were not. Increased bone resorption predicted hip fracture independently of bone mass, i.e., after adjustment for femoral neck bone mineral density (BMD) and independently of mobility status assessed by the gait speed. Women with both a femoral BMD value of 2.5 SD or more below the mean of young adults and either high CTX or high free D-Pyr levels were at greater risk of hip fracture, with an odds ratio of 4.8 and 4.1, respectively, than those with only low BMD or high bone resorption. Elderly women are characterized by increased bone turnover, and some markers of bone resorption predict the subsequent risk of hip fracture independently of hip BMD. Combining the measurement of BMD and bone resorption may be useful to improve the assessment of the risk of hip fracture in elderly women.