At your baby's 24th week, or his 6th month, you can expect him to develop dramatically in both physical size and physical abilities. Healthy babies can range dramatically in size, so you shouldn't worry if your 24-week-old is much larger or smaller than his peers. Also keep in mind that he might grow on a different timetable if he was born early.
Most babies grow an average of ½ inch to 1 inch every month and gain 5 to 7 oz. every week from birth until age 6 months, according to the Mayo Clinic. At that rate, your baby should just about have doubled her birth weight by 24 weeks. However, starting in her 6th month and until she is about 12 months old, her growth will slow down to an increase of about 1 cm in height a month and a gain of about 3 to 5 oz. a week.
Since healthy babies come in various sizes, no single weight is ideal for all babies. However, your pediatrician will use a growth chart to compare your baby's height, weight and head circumference with an average of all babies of the same sex and age, according to the Mayo Clinic. According to charts, a 6-month-old boy in the average percentiles for weight would weigh between 14 and 21 lbs. and any boy who is 28 inches long should be between 16 and 22 lbs., says Dr. Alan Greene of pediatric health website DrGreene.com.
Your 24-week-old's size is partially dependent on her health, but you most likely have nothing to worry about if she is smaller or larger than other babies her size. According to KidsHealth, her size and growth also depend on factors including: the genes you and your partner passed down to her, the amount and type of foods she eats and the functioning of the hormones that control different aspect of her growth.
Growth vs. Size
If your baby has always been in the 5th percentile for weight, he is most likely healthy but just on the small side. A steady, height-weight proportional growth pattern over time is more important than his size, says KidsHealth. The doctor may only be concerned if, for example, your baby was once at the 30th percentile for weight but, at the next visit, he has dropped down to the 5th percentile.
If you're concerned about your baby's size or growth, talk to her doctor. Be prepared with information such as how much and how frequently your baby eats every day, how long it takes her to nurse, what else your baby eats, the appearance and frequency of her bowel movements and the frequency of urination, says KidsHealth. If the doctor believes your baby's size may be an issue he will recommend a more in-depth evaluation.