Guest Author - Gwenn Schurgin O'Keeffe, MD, FAAP

Dear Dr. Gwenn:

My son is 3 months old now and his head measured 39 cm, between 5th and 10th percentile. He was born with 33cm, then 37 at first month and then 38.5 at second month. I've read through internet surfing that the head size is directly associated with brain development and that going below the 5th percentile may show problems.

I am fully breastfeeding. His current weight is 5714 grams and length is 62.5 cm. Based on the current WHO interactive measurement chart, weight to length is in the orange zone.

Should I start worrying? Should I start supplementing? Will this help brain growth?

Hoping for your quick response.

Thanks.
NW


Dear NW:

Thank you for your question. Before I address the details of your son’s measurements, I want to point out a few issues to consider. First, with growth parameters in babies, the trend is as important as the number. Are the measurements increasing along a particular growth curve consistently or have the measurements jumped up to a higher percentile curve or dropped to a lower one?

Second, there is huge room for error in infant measurements particularly with head circumference. To be accurate, the tape measure has to be at the widest parts of the head front and back. The widest part in the front is the forehead and the back just above the neck. If the tape measure is off just a touch, the measurement can be horribly inaccurate. Length can be similarly tricky as it is dependent on really straightening out a baby’s legs and marking the paper accurately. Weight is usually very accurate assuming the scale is zero’d.

Genetics and ethnic origin play huge roles in the size of babies and growth, as does good prenatal care. For the sake of discussion, I’m going to assume you had great prenatal care and a normal pregnancy and delivery.

I wouldn’t worry too much about supplementing yet but I would talk to your pediatrician and keep a close eye on your baby’s overall growth just because he is on the small side. But, the data really don’t point to a huge problem yet.

Looking at the standard CDC growth curve for male infants, your son was at the 10th percentile for head circumference at birth. At 2 months, his head circumference increased slightly to the 25th percentile curve. The 3month measurement, as you pointed out, is on the 5-10% curve. Assuming your son is growing and developing appropriately, the 2 month measurement could be falsely large or the 3rd month falsely low. It would be unusual to plateau so quickly in the setting of normal development. Plateaus do occur but are usually seen more gradually. So, I’d consider measurement error to be at play here to a degree. Incidentally, your son’s current weight and length fall on the 5-10th percentile range so having a small but proportionally head circumference would not by itself be a concern.

Future measurements will help you and your pediatrician see more clearly if there is a problem with head growth. If there is, rest assured your pediatrician will refer quickly to a specialist to help you sort out what is happening. One of the major purposes of all the visits during infancy is to monitor growth and development so you can trust your pediatrician – assessing these parameters is one of the cornerstones of our trade.

So, don’t panic yet. Continue to keep a watchful eye and stay in close touch with your child’s pediatrician.