Having a new baby is an exciting experience for any parent. When that baby arrives, one of the first things doctors and nurses will do is measure the length and weight of the newborn. This helps determine if the baby’s size is within the normal range or if they are considered small or large for their gestational age. So when is a newborn considered to be a tall baby?
What is the average length of a newborn baby?
According to the World Health Organization (WHO), the average length of a full-term newborn is about 51 cm or 20 inches. The normal range is generally between 48-53 cm or 19-21 inches. Babies born before 37 weeks gestation are considered premature and tend to be shorter in length. After 40 weeks gestation, babies are considered full-term.
Here are some key average newborn lengths according to gestational age:
- 37 weeks gestation: around 47 cm or 18.5 inches
- 38 weeks gestation: around 49 cm or 19.3 inches
- 39 weeks gestation: around 50 cm or 19.7 inches
- 40 weeks gestation: around 51 cm or 20 inches
- 41 weeks gestation: around 52 cm or 20.5 inches
- 42 weeks gestation: around 53 cm or 21 inches
As you can see, newborn length increases with gestational age. There is some normal variation among healthy newborns. But in general, babies born after 40 weeks gestation tend to be slightly longer than those born at 37-39 weeks.
What is considered a tall baby at birth?
There is no definitive cut-off for what is considered a tall newborn. However, many doctors define a “tall” baby as one whose length is above the 90th percentile for their gestational age and sex. The key factors are:
- Gestational age at birth
- Baby’s sex – boys tend to be slightly longer on average
- Growth curves – these track the range of normal growth
Using standard WHO growth charts, a newborn whose length is above the 90th percentile line would be considered tall or large-for-gestational age (LGA). Here are some examples of tall baby lengths by gestational age:
| Gestational Age | 90th Percentile Length for Boys | 90th Percentile Length for Girls |
|---|---|---|
| 37 weeks | 51 cm / 20 inches | 50 cm / 19.5 inches |
| 38 weeks | 53 cm / 21 inches | 52 cm / 20.5 inches |
| 39 weeks | 54 cm / 21.5 inches | 53 cm / 21 inches |
| 40 weeks | 56 cm / 22 inches | 55 cm / 21.5 inches |
| 41 weeks | 57 cm / 22.5 inches | 56 cm / 22 inches |
| 42 weeks | 59 cm / 23 inches | 58 cm / 23 inches |
So for example, a baby boy born at 40 weeks gestation measuring 57 cm or 22.5 inches long would be considered a tall newborn, since that length is above the 90th percentile for 40 week boys.
What causes a baby to be tall at birth?
There are several factors that can contribute to a newborn being tall or large-for-gestational age:
- Genetics – Babies born to tall parents tend to be taller. Genes play a major role in determining growth potential and adult height.
- Gestational diabetes – If the mother develops gestational diabetes during pregnancy, it can lead to extra growth and a larger baby.
- Maternal obesity – Women with obesity often have larger babies.
- Overdue pregnancy – Babies born after 40 weeks gestation have had more time to grow and gain length.
- Male sex – Baby boys tend to be slightly longer on average than girls.
- Placental abnormalities – Issues with the placenta function can overnourish a baby, leading to accelerated growth.
However, most of the time there is no identifiable cause. Some babies are just genetically predisposed to being longer and leaner. Monitoring fetal growth during prenatal visits can help identify potential issues.
Are there risks associated with a tall newborn?
In most cases, a tall newborn is perfectly healthy. However, some risks and complications can be associated with having a large-for-gestational age or macrosomic baby (usually defined as over 4,000-4,500 g or 8 lbs 13 oz to 9 lbs 15 oz):
- Difficult delivery – Tall babies may have a harder time fitting through the birth canal, increasing chances of shoulder dystocia.
- Birth injuries – Larger babies have higher risks of brachial plexus injuries and clavicle fractures during delivery.
- Low blood sugar – Macrocosmic babies are prone to low blood glucose levels after birth.
- Respiratory distress – Some large newborns may have trouble transitioning their breathing after delivery.
- Childhood obesity – LGA infants have a higher risk of being overweight later in childhood.
However, these risks are relatively low in babies who are just tall but not macrosomic. Extra monitoring and tests may be done for a significantly large newborn to check for any potential issues.
How is a tall baby measured at birth?
To determine if a newborn is tall or large for its gestational age, doctors will take two key measurements:
- Length – Measured crown to heel while the baby lies flat. Length is typically measured in centimeters.
- Weight – Baby is placed on a scale shortly after birth and weighed. Weight is measured in grams or pounds/ounces.
These measurements are plotted on a standard growth chart and compared to babies of the same gestational age and sex. If the length and/or weight falls above the 90th percentile for that baby’s age, they are considered large-for-gestational age (LGA) or macrosomic.
Head circumference may also be measured to check for appropriate growth. However, length at birth is the key factor in determining if a newborn is tall vs. average sized.
How tall do LGA babies grow up to be?
Research shows that babies who are born large-for-gestational age tend to remain on the taller side as they grow up. However, they usually do not end up exceptionally tall.
In one major study, babies defined as LGA were on average:
- 3.1 cm (1.2 inches) taller at 1 year old
- 4.8 cm (1.9 inches) taller at 2 years old
- 5.1 cm (2 inches) taller at 3 years old
By age 3, the height difference began to normalize compared to non-LGA babies. Other studies found similar trends of being moderately taller through early childhood.
However, genetics and mid-parental height still play the biggest role in final adult height. Most LGA babies are unlikely to become extremely tall like over 6 feet 5 inches (195 cm) as adults. But they tend to remain on the taller side of the normal spectrum.
Tips for caring for a tall newborn
Here are some tips for caring for a taller than average sized baby:
- Be prepared for potential delivery challenges – Discuss options like C-section with your doctor.
- Get checked for gestational diabetes – This may have contributed to larger growth.
- Monitor blood sugar after birth – Watch for signs of low glucose in a macrocosmic baby.
- Choose larger baby clothes – Onesies, sleepers, and diapers sized for bigger babies.
- Get safety gear for larger babies – Such as an oversized car seat, crib, and stroller.
- Support the neck during feeding – Large heads and weak neck muscles may make nursing challenging.
- Learn proper lifting techniques – Safely pick up and hold a heavier newborn to avoid injury.
- Feed on demand to fuel growth – Ensure your taller baby gets adequate nutrition.
While your tall newborn may present some unique challenges, with proper care there is no reason they cannot grow into a healthy, thriving toddler and child.
When to be concerned about a newborn’s length
It’s normal for new babies to come in a range of lengths. However, certain circumstances should prompt further evaluation:
- Length above 95th percentile – May signal an underlying growth disorder.
- Length below 5th percentile – Could indicate growth restriction.
- Disproportionate growth – An unusually large head or limbs could mean a skeletal disorder.
- No identifiable cause – Being LGA with no diabetes or obesity raises concerns.
- Dysmorphic features – Abnormal facial features may point to a genetic syndrome.
- Delayed development -Lagging motor skills, speech, or cognition alongside abnormal growth.
Testing may involve ultrasounds, genetic screening, hormone tests, or assessment by pediatric specialists. Early diagnosis of any underlying disorders or syndromes allows for better management and outcomes.
Conclusion
There are no strict cut-offs for declaring a newborn as tall or long. But babies whose length is above the 90th percentile for their gestational age are often referred to as large-for-gestational age or tall babies. Multiple factors like genetics, maternal health conditions, and the natural growth process all contribute to determining length at birth. While extra precautions may be needed for delivery and neonatal care, most tall babies go on to grow into proportionate, healthy children without major complications.