Understanding Prematurity
Prematurity refers to birth occurring before 37 completed weeks of gestation. Premature births are categorized by gestational age: extremely preterm (before 28 weeks), very preterm (between 28 and 32 weeks), and moderate to late preterm (between 32 and 37 completed weeks).
Measuring Premature Babies
A premature baby’s size directly correlates to their gestational age at birth. An infant born extremely preterm, around 24 to 25 weeks, might weigh approximately 1 to 1.5 pounds (450 to 680 grams) and measure about 10 to 12 inches (25 to 30 cm). This is comparable to the size of a small doll.
A baby born at 28 weeks might weigh between 2 to 3 pounds (900 to 1360 grams) and be around 13 to 15 inches (33 to 38 cm) long. Infants born closer to full term, at 32 to 34 weeks, typically weigh between 3.5 to 5.5 pounds (1.6 to 2.5 kg) and measure 16 to 18 inches (40 to 45 cm). A full-term baby typically weighs 5.5 to 10 pounds and measures 18 to 22 inches.
Factors Influencing Size
While gestational age primarily determines a premature baby’s size, other factors influence their birth weight and length. Intrauterine growth restriction (IUGR) can lead to a baby being smaller than expected. IUGR occurs when a fetus does not grow at the expected rate, often due to issues with the placenta or maternal health conditions.
Maternal health conditions also play a role. For example, severe preeclampsia or chronic hypertension can restrict fetal growth, resulting in a smaller baby. Conversely, maternal diabetes can sometimes lead to a larger-than-average baby for their gestational age.
Multiple gestations, such as twins or triplets, often result in smaller individual birth weights compared to singletons, as shared resources can limit the growth of each fetus. Genetic factors can also contribute to variations in size among premature infants.
Physical Characteristics of Premature Babies
Premature babies have distinct physical characteristics reflecting their incomplete development. Their skin is often thin, delicate, and translucent due to a reduced layer of subcutaneous fat, which normally develops later in pregnancy.
Many premature infants also have fine, downy hair called lanugo, especially on their back, shoulders, and ears. Their ears may feel soft and lack firm cartilage. Their feet and hands may have fewer creases than a full-term infant. Their heads often appear proportionally larger than their small bodies.
Growth and Development After Birth
After birth, the growth of premature babies is often evaluated using “corrected age” or “adjusted age.” This means subtracting the weeks or months a baby was born early from their chronological age. For example, a 6-month-old baby born two months prematurely would have a corrected age of 4 months.
This adjusted age helps healthcare professionals assess developmental milestones, as premature babies may reach them later than full-term infants. Many premature infants exhibit “catch-up growth,” an accelerated gain in weight or length that helps them narrow the size difference with their full-term peers. This catch-up growth typically continues into early childhood. Optimal nutrition and supportive care are important for promoting this accelerated growth and development.