Normal baby weight at birth

Updated April 13, 2017

Many factors influence whether an infant will have a low, high or normal birth weight. A baby born at full term usually weighs between 2.70 and 4.10 Kgs (6 and 9 pounds) and measures between 48 to 53cm (19 and 21 inches). (The average weight of a newborn is 7lbs. 8 oz.). It is important for an expectant mother to get prenatal care to monitor her baby's growth and take good care of herself to increase her chances of having a healthy baby.

What is low birth weight?

A baby who weighs less than 2.6kg (5lb. 8 oz.) is referred to as having a low birth weight. Infants weighing less than 1.6kg (3lb. 5 oz.) are classified as very low birth weight, while extremely low birth weight describes an infant weighing less than 1kg (2lb. 3 oz.). About 10 per cent of babies weigh less than 2.6kg (5lb. 8 oz.).

Causes of low birth weight

Not reaching full term and deficient development in the womb are the main reasons for low birth weight. Of all low birth weight infants, about 70 percent are born preterm--or before 37 weeks. Low birth weight babies born at full term had deficient development in the womb.

Factors that increase the risk for a low birth weight baby include: having multiple babies at once; using drugs and alcohol; smoking; stress; abuse; exposure to hazardous substances; fatigue; insufficient nutrition; past abortions or preterm deliveries; bladder or vaginal infections; and the mother's age when she gets pregnant (a woman who is younger than 20 or older than 45 has a higher risk).

What is High Birth Weight?

Macrosomia, which means "large body," is the term for an infant with an unusually high birth weight. Macrosomia is defined as a birth weight of 3.7kg (8lb. 13 oz.) or more. High birth weight infants weighing more than 4.08 Kg (9 pounds) are in the 90th percentile for weight and called "large for gestational age" (LGA).

Approximately, 10 per cent of infants weigh more than 3.7kg (8lb. 13 oz.) at birth. Most LGA babies are born between the 37th and 41st week of pregnancy.

Causes of high birth weight

Medical problems, such as gestational diabetes, the mother's size (particularly if she is heavy), or genetics can lead to LGA. Excessive weight gain in pregnancy and obesity (even before pregnancy) are also risk factors for macrosomia.

The incidence of macrosomia increases in pregnancies that go beyond 40 weeks. A woman who has given birth to an LGA infant in the past is 5 to 10 times more likely to deliver an LGA baby. A woman who has given birth two or more times has a greater risk for an LGA baby than a first-timer. And ethnicity has been found to be a factor.

How to increase your chances of having a normal weight baby

Taking good care of your health before and during pregnancy can go a long way toward having a baby with a normal birth weight. Eat a balanced diet with plenty of fruits and vegetables and go easy on high-fat, non-nutritional foods. Avoid drugs, alcohol and cigarettes before and during pregnancy. Stay active throughout your pregnancy, incorporating low-impact exercise into your daily routine. Get sufficient rest and avoid getting unduly stressed.

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About the Author

Wanda Brito was born to write. She has written professionally since 1998 - developing surveys, presentations and marketing research reports — and has been writing and proofreading freelance since 2007. Her work has been featured on She holds a Bachelor of Arts in Spanish literature from Colgate University and a Master of Science in administration from Metropolitan College of New York.