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Penn Nursing > Media > Infant Growth Curves

New growth curves for premature infants reflect the racial diversity of the U.S.

The infant growth chart used for decades by doctors, dietitians and hospitals to determine the healthy weight of infants may be incorrect for use today, says a new study from a University of Pennsylvania School of Nursing professor, whose latest research provides new healthy weights that reflect the racial diversity of U.S. births.

“The currently used curves may not represent the U.S. population,” says lead author and Adjunct Assistant Professor Irene Olsen, PhD, RD, LDN, who developed a new set of weight, length, and head circumference-for-age growth curves to assess preterm infants in NICUs. The new growth curves were published in the February issue of Pediatrics, The American Academy of Pediatrics’ journal.  

Since the 1960s, pediatrics has relied on growth statistics derived by Dr. Lula Lubchenco, known familiarly as the "Lula Gram" or "Lubchenco Curves." Dr. Olsen's research has expanded far beyond the 5,000 nearly all-white babies Dr. Lubchenco measured in Denver at mid-Century ro records of more than 400,000 babies from 1998-2006 that reflect the diversity of American children. If taken as the standard, they may well become the "Olsen Curves."  

Dr. Olsen found that the currently used Lubchenco curves typically:

  • Underestimate the percentage of small (SGA, small-for-gestational-age) infants
  • Overestimate the percentage of small females (less than 36 weeks)
  • Consistently underestimate the percentage of younger infants (less than 36 weeks) who are large for their gestational age

 On average, the new curves, have:

  • Lower average weights, lengths, and head circumferences at younger gestational ages than the Lubchenco curves until 30-36 weeks
  • Higher average growth measurements at older gestational ages

“The misclassification we found using the old Lubchenco unisex curves may lead to many small infants not receiving the care they need because they are classified as average; younger but larger infants may be overlooked because they are misclassified as average; and older infants may be mistakenly targeted for extra NICU attention since they are misclassified as large,” said Dr. Olsen.

Small-for-gestational-age (SGA) and large-for-gestational-age (LGA) are commonly used to define high-risk groups of infants who receive extra attention in the NICU. SGA infants are at risk for growth and neurodevelopment delays, and LGA infants are at risk for early hypoglycemia and later metabolic syndrome.