Ideal Weight for a 5.5-Month-Old Male Infant
For a healthy, full-term 5.5-month-old boy, the ideal weight range is approximately 6.5-9.0 kg (14.3-19.8 lbs), with the median (50th percentile) being around 7.5 kg (16.5 lbs) according to WHO growth standards. 1
Growth Standards for Infants Under 6 Months
The World Health Organization (WHO) growth charts should be used for all infants under 24 months of age, regardless of feeding type, as these represent optimal growth standards based on healthy, predominantly breastfed infants from six countries living in optimal conditions 2, 1
The WHO charts include longitudinal data collected more frequently during the first months of life when growth is most rapid, making them particularly appropriate for assessing a 5.5-month-old infant 1
Expected Weight Parameters at 5.5 Months
Normal weight at 5.5 months typically falls between the 2.3rd and 97.7th percentiles (labeled as 2nd and 98th percentiles on growth charts), and values outside these ranges may indicate adverse health conditions requiring evaluation 1, 3
At approximately 5-6 months, most infants have doubled their birth weight, with the mean age of birthweight doubling being 119 days (3.8 months) for the entire population 4
Boys typically double their birthweight earlier than girls (111 days vs. 129 days), which should be considered when assessing growth at 5.5 months 4
Feeding-Related Growth Considerations
Breastfed and formula-fed infants show different growth trajectories that are both normal: breastfed infants typically gain weight faster than formula-fed infants during the first 3 months, then more slowly after 3 months 1
Formula-fed infants tend to gain weight more rapidly after approximately 3 months compared to breastfed infants, and bottle-fed infants doubled their birthweights earlier than breast-fed infants (113 days vs. 124 days) 2, 4
Using WHO charts helps prevent inappropriate recommendations to supplement or wean breastfed infants who are growing normally but more slowly after 3 months 1
Clinical Monitoring Recommendations
Serial measurements are more informative than single measurements when assessing growth adequacy 1
Values below the 2.3rd percentile (2nd percentile on charts) warrant evaluation for underlying causes, including thorough feeding history, review of previous growth measurements, and assessment for gastrointestinal symptoms 1, 3
A drop of 40 percentile points represents clinically significant growth faltering requiring intervention before reaching the 2nd percentile 1
Important Caveats
Growth charts represent a range of normal, not a target, and healthy children naturally distribute across all percentiles 5
Consistent percentile tracking is the key indicator of healthy growth—when a child maintains their growth along the same percentile curve over time, this represents normal constitutional growth 5
Family growth patterns should be assessed to determine if a child's percentile reflects genetic potential 5