Abstract
Objective The objectives of this study were to describe (1) body mass indexes (BMIs) using
weight and length for gestational age (GA) classifications, and (2) the additional
information BMI, as a measure of body proportionality, provides for preterm infant
growth assessment and care plans at birth.
Study Design Birth weight, length, and BMI of 188,646 preterm infants (24–36 weeks gestation)
admitted to U.S. neonatal intensive care units (Pediatrix Clinical Data Warehouse,
2013–2018) were classified (Olsen curves) as small, appropriate, or large for GA (SGA < 10th,
AGA 10–90th, LGA > 90th percentile for GA, respectively). The distribution for the
27 weight–length–BMI combinations was described.
Results At birth, most infants were appropriate for weight (80.0%), length (82.2%), head
circumference (82.9%), and BMI (79.9%) for GA. Birth weight for GA identified approximately
20% of infants as SGA or LGA. Infants born SGA (or LGA) for both weight and length
(“proportionate” in size) were usually appropriate for BMI (59.0% and 75.6%). BMI
distinguished disproportionate weight for length in infants with SGA or LGA weight
at birth (58.3%, 49.9%). BMI also identified 11.4% of AGA weight infants as small
or large for BMI (“disproportionate” in size) at birth; only using weight for GA missed
these underweight/overweight for length infants.
Conclusion The unique, additional information provided by birth BMI further informs individualized
preterm infant growth assessment by providing an assessment of an infant's body proportionality
(weight relative to its length) in addition to the routine assessment of weight, length,
and head circumference for GA and may better inform care plans and impact outcomes.
Key Points
-
Most preterm infants were born AGA for all growth measures.
-
AGA weight infants may be under- or overweight for length.
-
BMI distinguished body disproportionality in SGA/LGA infants.
-
Recommend BMI assessed along with weight, length and head.
-
Further research on BMI in preterm infants is needed.
Keywords
body mass index - preterm infants - body disproportionality - disproportionate - symmetric
- asymmetric - weight for length ratio - small for gestational age - large for gestational
age
