Every baby gains weight at a different rate, but most follow a pattern falling within a set range for their age. These ranges are found on growth charts used by health care professionals who see infants and children for periodic well-child checkups. Kids Health explains that many factors contribute to growth and development, including nutrition, physical activity and genes. At 14 weeks of age, a baby will have grown several ounces and possibly a few pounds since birth.
Significance of Birth Weight
The weight of a 14-week-old baby depends on her birth weight. It is possible for the baby to grow rapidly or slowly after birth causing her to reach a new percentile on the growth charts. For example, a baby who is in the 80th percentile at birth may gain weight like an average baby, causing her to drop down into the 70th percentile or lower. Kids Health points out that health care professionals do take into account the average weight of a 14-week-old, but the pattern of the individual baby's growth plays an important role in considering her growth normal or abnormal.
Effects of Pregnancy
Several factors in pregnancy can contribute to a baby's birth weight and his weight later in the year. Kids Health warns that mothers who have high blood pressure, cardiovascular problems, smoke, drink alcohol or use illegal drugs during pregnancy increase the risk of a low birth weight baby. Conversely, mothers with diabetes, poor eating habits or who gain too much weight in pregnancy can increase the risk of having a large baby. Either of these situations can produce a baby who goes on to live a healthy life, but his expected weight at 14 weeks of age may lie outside the average range.
Average Weight at 14 Weeks
MedlinePlus points out that health care professionals often see babies at 8 weeks of age and then again at 16 weeks of age. A 14-week-old baby is in between these two appointments, but will still weigh close to what she should at her 16-week appointment. According to KidsGrowth.com, the Centers for Disease Control and Prevention considers a 12-week-old baby to be in the 50th percentile, or average, when she weighs about 12 lbs. The same aged boy will be in the 50th percentile if he weighs 13 lbs. By the 14th week of life, an infant is probably gaining about 5 oz. a week or 2/3 oz. per day, states Kids Health.
Weighing slightly above or below the 50th percentile is perfectly normal. Babies go through growth spurts at about the same time, but there can still be some variation. A premature infant, meaning he was born at least three weeks prior to his estimated due date, can start at a lower birth weight. Some premature infants take longer to catch up to their full-term counterparts while others can catch up quickly due to establishing a good eating routine.
An infant born with or suffering from an illness during the first 14 weeks of life can grow at a slower rate than he normally would. This can cause the growth chart to reveal an unsteady weight gain, which is more concerning than an infant falling below the 50th percentile on a consistent basis. When these situations arise, a health care professional will examine the situation closely to determine the cause of the poor weight gain.
Failure to Thrive
Failure to thrive can be a serious health complication for a baby in the first year of life. This diagnosis is given when a baby misses multiple growth milestones, states Kids Health. So a baby who has not doubled the birth weight by 4 months of age or tripled it by age 1 may be failing to thrive. There are various reasons this may occur, including poor nourishment, inadequate nurturing and stimulation from caregivers and various health conditions, including thyroid disorders.