How Tall Will My Baby Be? A Genetic Explanation
When a soon-to-be-parent learns they’re expecting a child, their brains go into overdrive—including wondering what—or who!—their child will look like. Brown hair? Blonde hair? Red hair? No hair? Which may trickle into pondering about height—will baby be tall or short like me/the other biological parent?
I confess: I definitely wondered, and still do: How tall will my baby be?
Since we were just as curious as you, we asked doctors to break down the height gene that determines how tall or short your kid MIGHT be.
How Parents’ Height Impacts Baby
“Parental height does have an influence on predicting a child's height,” summarizes Dr. Swati Sharma, a Denville, NJ-based endocrinologist. Here’s why: “Many formulas have been proposed as to how to determine baby’s eventual height.”
According to Dr. Sharma, the most common way to determine is by adding both parents heights (inches), then either add 5in (males) or subtract 5in (females), and then divide in half.
How Your Family Tree Impacts Your Baby’s Height
“Genetics play the largest contributing role in determining your adult height,” says Dr. Sharma. “Some sources say up to 80% of your adult height is genetically predetermined.”
No one particular gene has been identified, though. “Height is a polygenic trait, meaning multiple genes are involved,” explains Dr. Sharma. “Some genes play a larger role than others—this is mostly seen in some very rare genetic disorders which result in extreme aberrant height.”
Generally, she adds, the effect of any single gene location is small, but the effect of variants at these multiple genes all together can predict if an individual will ultimately be on the shorter or taller side of the average adult height spectrum.
“Children inherit these genetic variants from their parents but not always in the same combination—thus, not all siblings will end up being the same height.”
For example, I myself am the oldest of 4 children from the same mom and dad, and I am the smallest, at 5’5, height-wise, compared to my taller siblings. Also, if you watch Keeping Up With the Kardashians, you will notice eldest sibling Kourtney is shorter than her younger siblings. Meaning: The oldest sibling is certainly not always the tallest once they ease into adulthood.
External Factors That Impact Height
Let’s not ignore the external factors that can impact your baby’s eventual height.
“Environmental factors such as maternal smoking, breastfeeding, maternal age, social class, maternal education, and parental divorce had an effect on offspring height in generations prior to 1958 according to a study out of Great Britain. Children’s height in generations after 1958 was most strongly correlated with parental height,” says Dr. Kimberly Langdon, an Ohio-based OBGYN and medical advisor at Medzino, a digital health company.
Dr. Sharma agrees, adding: “Poor maternal nutrition while in-utero and maternal smoking in particular definitely has a negative impact on fetal growth. There is an increased risk for prematurity, small for gestational age babies, and has also been linked to short stature and obesity in adulthood.”
How Growth Hormones Impact Height
According to Dr. Sharma, if one suspects that his/her child may need growth hormone, the first thing to do is discuss this with the child's pediatrician and determine if a referral to a pediatric endocrinologist is warranted.
“The child's bone age will need to be determined (through X-rays typically) to see if it corresponds appropriately to the child's chronological age.”
Also, she adds, a comprehensive evaluation for the hormone involved in growth and metabolism should take place, which typically includes testing for thyroid hormone, sex hormones (estrogen and testosterone), adrenal and pituitary function (which would include growth hormone).
Wondering how big your baby will be or how much they will weigh? Check out this thorough guide on the genetic and non-genetic factors that can impact baby's weight at birth.