Percentile curves for Botswana- compared to U.S.- born black babies. Percentiles using a B-spline with knots at 24, 26,28,38,40,44 weeks (black); published percentiles for black U.S.-born babies shown in gray*. * Oken E, Kleinman KP, Rich-Edwards J, Gillman MW. A nearly continuous measure of birth weight for gestational age using a United States national reference. BMC Pediatrics 2003;3:10.