At birth, a baby can weigh between 6 lbs 2 oz and 9 lbs 2 oz on average, states KidsHealth. There are many factors that can contribute to variations in the newborn's weight, including the gestational age of the baby at birth, the size of the parents, if the baby shared the womb with siblings, the baby's gender and the mother's health during pregnancy. Infants should grow at a relatively steady rate after birth, making it difficult to identify exactly what a baby should weigh at six weeks of age.
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Significance of Birth Weight
A baby's birth weight sets the baseline for weight gain for the next year. When a baby is above or below average in weight at birth, then she may continue to be so at six weeks of age. Some babies will catch up or slow down in weight soon after birth, making them fall into the average range of weight on growth charts. Within a few days of being born, a healthy newborn will lose about 7 to 10 percent of her birth weight, states KidsHealth.org. This will be regained by the second week of life.
Function of Pregnancy Conditions
KidsHealth.org explains that a mother with health conditions such as high blood pressure or heart problems, or who uses cigarettes, alcohol or illegal drugs during pregnancy will likely give birth to a child with a low birth weight. Conversely, mothers with diabetes, including gestational diabetes, can have larger babies. Eating poorly, including eating too much or missing out on important nutrients, can impact a baby's birth weight. A baby has a good chance of reaching the average weight range after birth if an adequate eating routine has been established throughout the pregnancy.
A baby will gain about 5 oz. per week after birth, according to KidsHealth. This rate of gain may be steady with several growth spurts, where the baby gains weight rapidly, occurring after the first, third and sixth weeks of life. A baby following this pattern will have gained about two pounds after birth by the sixth week of life, making the ideal weight range between eight and 11 pounds.
All babies are different and may gain at a faster or slower pace than their peers, depending on various factors. Some babies may not establish a strong feeding routine by the sixth week. Due to being born early, a premature baby may not hit the typical growth spurts until sometime after the expected due date. This means a baby born five weeks early may not have the three-week growth spurt until she is actually eight weeks old. Most premature infants will catch up with full-term babies within the first year, states FamilyDoctor.org.
A baby can be considered perfectly healthy when his weight is below the standard for his age, but there are times when failing to gain weight is a concern. DrGreene.com describes this condition as failure to thrive. When a six-week-old baby has not gained weight that is in line with his head circumference or length, a health care professional may take action. Sometimes this lack of gain is due to genetics, but it can also be the result of poor nutrient absorption or inadequate caloric intake.