Chapter 7: NEONATOLOGY

WEIGHT, LENGTH, & HEAD CIRCUMFERENCE

NEWBORN WEIGHT

Newborns should double their birth weight by 4–6 months and triple their birth weight by 1 year of age. For a full-term baby, expect weight gain of 20–30 g/day. For preemies, expect weight gain of 15–20 g/day. For LGA and SGA versus LBW, VLBW, and ELBW, remember that the ones who have “GA” are based on a newborn’s Gestational Age. The ones with “LBW” are simply based on the absolute weight in grams.

• PEARL: 50th Percentile for WEIGHT at birth is 3.25 kg for a full-term baby
• LARGE FOR GESTATIONAL AGE (LGA): Top 10^th percentile for weight, or > 3900 grams at birth for a full-term baby.
• SMALL FOR GESTATIONAL AGE (SGA): Bottom 10^th percentile for weight, or < 2500 grams at birth for a full-term baby.
• LOW BIRTH WEIGHT (LBW): < 2500 grams
• VERY LOW BIRTH WEIGHT (VLBW): < 1500 grams
• EXTREMELY LOW BIRTH WEIGHT (ELBW): < 1000 grams
  • PEARL: A baby that is ELBW can be “AGA” if it is a premie.

PREDICTED GROWTH RULES OF THUMB

Here are some great shortcuts to help you calculate the expected length for children:

• 1-year-old: 1.5x the birth length
• 4-year-old: 2x the birth length
• 13-year-old: 3x the birth length
• Midparental height: Estimates the child’s genetic growth potential after adjusting for the child’s sex. Then a “target height” range can be obtained. Please note that there are many algebraic ways to get to the final answer. For simplification, add height before averaging for boys and subtract height before averaging for girls.
  • Boys = (Mom’s Height + Dad Height + 5 inches)/2. If given cm, use 13 cm.
  • Girls = (Mom’s Height + Dad Height – 5 inches)/2. If given cm, use 13 cm.
  • Alternate, equivalent method: boys’ predicted height = average parental height + 2.5 inches, girls’ = average parental height – 2.5 inches.
  • For boys and girls, approximately 2–3 inches (5–8.3 cm) on either side of that calculated height represents a range of height that would be considered normal based on genetics. Some authors use 2 inches, others use 3.3 inches.
• PEARL: 50th Percentile for LENGTH at birth is 50 cm.
• PEARL/EXAMPLE: The most average baby you can find would be 50 cm in length at birth and by 1 year of age s/he would be 75 cm. By 4 years old, s/he would be about 100 cm (2 x 50), and by 13 s/he would be 150 cm (3 x 50). 150 cm / 2.5 = 60 inches = 5 feet.

INTRAUTERINE GROWTH RESTRICTION = INTRAUTERINE GROWTH RETARDATION = IUGR

The term intrauterine growth restriction, AKA intrauterine growth retardation or IUGR, is not the same thing as “small for gestational age” (SGA). IUGR is used to describe intrauterine fetal growth that has deviated from the norm because of some pathological condition. SGA refers to babies with a weight that is less than the 10^th percentile for ALL babies at that gestational age, even if that baby is constitutionally small and without any pathology. “IUGR” aims to identify fetuses that are at high risk for poor outcomes so that appropriate interventions may be pursued (if possible). So, a fetus at the 20^th percentile for weight could have intrauterine growth restriction resulting in a decline in the percentile of weight to the 12^th percentile. That fetus would not be considered SGA because it is greater than the 10^th percentile. At birth, IUGR babies can have a presentation similar to that of an Infant of a Diabetic Mother (hypoglycemia, polycythemia, poor feeding, and hypothermia).