Hoffman weight for gestational age criteria, by gender and race
from: " Analysis of Birth Weight, Gestational Age, and Fetal
Viability, U.S. Births, 1968" H. J. Hoffman, C.R. Stark,
F. E. Lundin, and J.D. Ashbrook, Obstetrical and
Gynecological Survey, Vol 29, No. 9, pp 651-681 , 1974
"Birthstat" is a SAS program to calculate newborn
weight for gestational age status, by gender and race, using
standard criteria based on a sample of U.S. births in 1968.
(as published by Hoffman, et al (1974); as above).
The program is offered by Karen Norberg, MD; e-mail firstname.lastname@example.org
Issues to keep in mind:
This program calculates 10th and 25th weight percentiles by
gestational age, gender and race,
over gestational ages ranging from 22 - 52 weeks.
Note: 1 gram = .035 oz; 1 oz = 28.349 grams
- These criteria are based on a 50% sample of single, live
births reported by 36 states and the
district of Columbia in 1968, the first year of a revised
US standard birth certificate that included report of date
of last menstrual period.
- In spite of the large sample on which this table is based,
the 10th percentiles at extreme gestational
ages are based on small numbers in this data; some
nonlinearities probably reflect random variation.
Other nonlinearities probably reflect true underlying effects
in the population; for example, mean birthweights at
very low gestational ages are higher than
expected from a linear extrapolation from
later gestational ages; this reflects
the high mortality rate among very premature infants. Only
those very premature infants of somewhat greater weight are
likely to survive the birth process.
- These criteria represent a historical standard,
against which later birth cohorts may be compared. Some
"paradoxical" historical effects could occur. For
example, improvements in medical care may result in lower
rates of prematurity, and higher birth weight for a particular
gestational age, but also higher rates of survival from
prematurity, and higher rates of survival
for lower weight infants at any particular
gestational age. As a result, improvements in medical care
could result, in theory, in higher rather than lower rates of
intrauterine growth retardation among live born infants.
- There is controversy about whether racial differences in
birthweight in the U.S. are the result of economic or social
factors, or reflect "true" biological variations
among different ethnic populations. Investigators
may wish to use the black/white distinction, or not,
depending on the purposes of the study. However, differences
in birthweight by gender are well established and clearly
have a biological basis.
- There are other weight standards available; this table is
chosen because it reflects a nationally representative
sample, not selected for the presence or absence of
prenatal illness or congenital malformations, and is the
largest published sample. Other standards may be more
appropriate for particular purposes .
conventional cutoffs for gestational age are:
less than 37 or 38 weeks = premature;
more than 42 weeks = postmature;
sex 1 = male
2 = female
black 0 = other
1 = black
hs10 1 = equal to or below tenth percentile of weight for gestational age
0 = above tenth percentile
hs25 1 = equal to or below 25th percentile of weight for gestational age
0 = above 25th percentile
Download SAS code