Birth Weight

Birth weight is one of the handful of statistics many new parents tell their friends and family about their new baby – along with length, time of birth, gender, and name. If your baby is born within the normal range of weight for his or her gestational age, he or she is said to be AGA, or appropriate for gestational age. However, some babies are born outside of the AGA – either too big or too small – which can be caused by a variety of factors, some benign and others serious.

Low Birth Weight

One in 13 babies is born with low birth weight - also referred to as small for gestational age (SGA)- which is a factor in 65 percent of all infant deaths, according to the March of Dimes. A baby is considered to have low birth weight if he or she weighs less than 5 lbs. 8 oz. at birth (2500 grams).

There are two categories of low birth weight:

Preterm birth – Babies born before 37 weeks are considered preterm and account for more than 60 percent of low birth weight babies.

Growth restricted – Babies who are full-term but underweight may have suffered from slowed or restricted growth in the womb. Growth restriction may be caused by several things, including:

• Environmental factors, such as maternal smoking, drinking or drug use and poor nutrition

• Severe anemia

• Preeclampsia

• Chromosomal abnormalities

• Infections (such as syphilis, toxoplasmosis, or rubella)

• Twins or multiple births

There are two sub-categories of growth restriction: symmetrical and asymmetrical growth restriction. A baby with symmetrical growth restriction will be born with a head that is in proportion to the rest of his or her body, which indicates he or she developed slowly throughout the pregnancy. Causes of symmetrical growth restriction include early intrauterine infection, chromosomal abnormalities, and maternal substance abuse. A baby born with asymmetrical growth restriction developed normally for the first two trimesters, but was stalled in the third, often due to preeclampsia. Such a baby has a thin, small body but large head; dry, peeling skin; and a thin umbilical cord.

Although scientific studies have been conflicting, babies with low birth weights are thought to be at greater risk for type 2 diabetes, obesity later in life (as are babies with high birth weight), and lower intelligence.

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