Average Baby Length in the First Year: What to Expect
Your pediatrician will measure your baby for length at each appointment. This is an important measurement, but your doctor will likely be most concerned that your baby is gaining weight each month.
Infants should double their birth weight by age 5 months, and triple their birth weight by one year. Learn more about the average weight for male and female babies by month.
Remember, babies go through growth spurts. Your baby’s month-to-month progress on the growth chart isn’t as important as the trend of their curve overall.
If your child fails to grow or their growth has slowed during their first year, your doctor may refer you to a specialist. An endocrinologist may take blood tests, X-rays, or body or brain scans to determine why your baby has stopped growing.
In rare cases, your doctor may want to test your baby for:
Your doctor can recommend medications or hormone injections, if necessary.
Babies who are born prematurely often, though not always, weigh less than full-term babies. A baby is considered full-term if they’re born at or after 39 weeks of gestation.
Every week makes a difference. A baby born at 24 or 25 weeks will weigh less than a baby born at 28 or 29 weeks.
If your baby is premature, they may have a low birth weight or very low birth weight:
- Babies born at a low birth weight weigh between 3 pounds, 5 ounces (1.5 kilograms) to 5 pounds, 8 ounces (2.5 kilograms) at birth.
- Babies born at a very low birth weight weigh less than 3 pounds, 5 ounces at birth (1.5 kilograms) at birth.
Premature babies require more medical attention and support when they’re born. They often stay in the neonatal intensive care unit (NICU) until they’re healthy enough to go home. This often occurs near their original due date.
The ability to gain weight steadily will be necessary before your baby can go home. Often, though not always, babies are kept in the NICU until they weigh at or near 5 pounds.
Just like all babies, preemies lose some weight after birth and then begin to gain the weight back. While your baby is in the NICU, you’ll likely be able to supply them with pumped breast milk.
Babies don’t develop the sucking reflex until 32 weeks old, so babies born very early are given milk through a tube into their stomach at first. Your baby can also drink formula this way.
Weight gain is an important measure of health for premature infants. If there are no underlying health issues that make it difficult for your baby to grow, they’ll gain weight steadily.
Based on their level of prematurity, for the first few weeks, the amount of weight gain may be similar to the amount of weight they’d be gaining were they still in utero.
Premature babies grow and gain weight at a faster rate than full-term babies do. During their first year, premature babies are measured for weight based on the age they would’ve been born at term rather than by their actual birth date.
For example, if your baby is born at 35 weeks, when they’re 5 weeks old, their doctor will refer to the newborn weight percentiles instead of those for a baby that’s 5 weeks old.
Many premature babies catch up to full-term babies in terms of weight by their first birthday. Some may not catch up until they’re 18 to 24 months old.
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The average weight for a baby born in the UK is 7lb 8oz for boys and for girls 7lb 4oz.
Prince Louis weighed 8lb, 7oz when he was born — putting him on the upper end of the normal scale.
Prince Harry and Meghan Markle’s baby Archie weighed 7lbs 3oz at birth.
A newborn who weighs more than 8.8lbs is considered larger than normal — and may be referred to as macrosomia.
These babies are often born to mums who developed gestational diabetes while pregnant.
You may also have a big baby if you:
- Were a big baby yourself
- Were overweight before becoming pregnant
- Have gained a lot of weight during pregnancy
- Give birth two or more weeks after your due date
A baby who’s born at full term will normally be between 50-53cm long, with an average length of 51cm.
Tots who have tall parents are often longer, and vice versa for short parents.
What makes your baby weigh more or less than the newborn in the next bassinet? Several factors come into play: