Are all Growth-Retarded Newborns Created Equal(ly)? • 449

Background: Previous etiologic studies have defined intrauterine growth retardation (IUGR) based on a single cut-off (usually <10th centile) of birth weight for gestational age.

Objective: To assess the relative importance of etiologic determinants of IUGR according to the degree (severity) of fetal growth restriction.

Design/Setting: Cohort study based in a tertiary-care university hospital.

Participants: Singleton live births between 1 January 1980 and 31 March 1989 with early ultrasound-validated (±7 days) gestational age(n=13,139).

Measurements: Comparison of adjusted odds ratios (ORs) and 95% confidence intervals for any IUGR (defined as <85% of the mean birth weight for gestational age, equivalent to the 9.8th centile for this cohort) and severe IUGR (<75% of the mean = 1.5th centile), after controlling for maternal age, education, marital status, and other known and suspected determinants of IUGR by means of multiple logistic regression analysis.

Results: The strength of the association with any IUGR and severe IUGR was similar for maternal short stature (<157.5 cm), prepregnancy BMI<19.8 or >26.0-29.0 (vs reference of 19.8-26.0) kg/m², low rate of net gestational weight gain (≤0.17 kg/wk), and prepregnancy hypertension. The effects of several determinants, however, were much stronger for severe IUGR than for any IUGR: OR=13.5 (6.2-29.1) vs 3.1 (1.7-5.6) for severe pregnancy-induced hypertension (PIH), 4.5 (2.8-7.4) vs 2.3 (1.8-2.9) for smoking >10 cigarettes/day, and 3.2 (2.0-5.0) vs 1.7 (1.5-2.0) for primiparity. Conversely, the protective effect of prepregnancy obesity (BMI>29.0 kg/m²) for any IUGR [OR=0.5 (0.3-0.8)] was not apparent for severe IUGR [OR=1.3 (0.6-2.8)].

Conclusions: Anthropometric/nutritional determinants and prepregnancy hypertension appear to act across the continuum of fetal growth restriction, whereas the effects of primiparity and pathologic determinants such as cigarette smoking and PIH are more pronounced with more severe degrees of IUGR. Growth-retarded newborns are not, therefore, all created equal(ly).