Growth charts, percentiles and the baby milestones that matter

A growth chart shows whether your baby is growing steadily along her own line, not whether she is "big enough". A baby on the 15th percentile can be just as healthy as one on the 75th. Milestones work the same way: each comes with a range. What matters is steady progress, and a few clear warning signs that should never be met with "let us wait and see".

Which growth chart is used for Indian babies?

For children under 5, the IAP recommends the WHO Child Growth Standards.¹ For ages 5 to 18, it uses its own charts based on Indian children.¹

The WHO charts were built from healthy breastfed babies raised in good conditions in six countries, including India.² So they show how children grow when given a good start, not just how an average population happens to grow.³

A striking finding was how alike healthy children were across very different countries. Only about 3% of the variation in length came from which country a child lived in.² That is why one chart can be used for children everywhere.³

Boys and girls have separate charts for weight, length and head size. Babies born early should be plotted by their corrected age, counted from their due date.

What does my baby's percentile mean?

A percentile compares your baby with 100 healthy babies of the same age and sex. On the 25th percentile, about 25 of them weigh less and 75 weigh more.

It is not a school mark. The 25th percentile is not "25 out of 100". A baby on the 10th percentile is as healthy as one on the 90th, if both grow steadily along their lines and their weight fits their length.

Doctors also use z-scores, which say how far a child is from the average in standard steps. The WHO charts give both percentiles and z-scores.³

Small parents often have small babies. That is not a problem to fix with extra feeds.

What matters more than the percentile number?

The pattern over time. A baby who follows her own line is growing well, whatever the line.

• Most babies settle into their own channel during the first year.
• Some drift in the early months. A big baby born to small parents may move down a line or two, and that can be normal.
• Weight that falls well below the length line can mean undernutrition.
• Length falling as well can mean a longer-standing problem.
• A head size that is very small, very large, or crossing lines needs a check.

A single weight on a different scale, with the baby in clothes, tells us little. Weights on the same scale, without clothes and nappy, tell us a lot.

How much weight does a newborn lose, and when is it regained?

Most newborns lose some weight in the first few days. This usually stops by day 3 or 4, and most babies are back to birth weight by 3 weeks.⁴

A loss of more than 10% of birth weight needs a feeding check and a look for illness or dehydration.⁴ In a study of over 100,000 breastfed newborns, almost 5% of babies born vaginally and more than 10% born by caesarean had lost 10% or more by 48 hours.⁵ Babies born by caesarean tend to lose a little more.⁵

If your baby has not regained her birth weight by 3 weeks, your doctor should review her feeding and health.⁴

How much weight should my baby gain each month?

There is no single right number. Gain is fastest in the first 3 months, then slows through the first year. The growth chart, not a fixed target, is the best guide.

Comparing your baby with a cousin or a neighbour's child tells you nothing useful. Comparing her with her own line on the chart tells you a great deal.

Growth slows a lot in the second year. Toddlers often seem to eat less. This is normal, and it is the most common reason families tell Dr Dutta their one-year-old has "stopped eating".

What is faltering growth or failure to thrive?

Faltering growth (once called failure to thrive) means a baby is gaining weight more slowly than expected for her age and her starting point.⁴

UK guidance suggests concern when a baby's weight drops across centile lines on the chart. How many lines depends on where she started:⁴

• 1 or more line spaces if her birth weight was below the 9th centile
• 2 or more if it was between the 9th and 91st
• 3 or more if it was above the 91st
• any baby whose weight is below the 2nd centile

UK guidance advises a detailed feeding history, sometimes watching a feed, and further tests only when there is a reason.⁴ In Dr Dutta's experience, feeding is the most common problem she finds.

What happens at a well-baby check-up?

Your doctor weighs and measures your baby, plots her on the chart, examines her, asks about feeding, sleep and development, and gives vaccines due.

In India these visits often line up with the vaccine schedule: birth, 6, 10 and 14 weeks, then 6, 9, 12, 15 and 18 months. Each is a chance to ask questions. Bring a list.

The AAP advises a quick check on development at every visit, plus a formal screening test at 9, 18 and 30 months.⁶ It also advises autism screening at 18 and 24 months.⁷ If your paediatrician does not mention these, ask.

Bring the growth chart and vaccine card to every visit, from every clinic.

Are milestones fixed ages?

No. Each milestone has a range, and healthy children vary widely. The ages often quoted are averages, not deadlines.

In 2022 the CDC and AAP revised their milestone checklists. Each milestone is now set at the age by which most children, at least 75%, can do it.⁸ This was done to discourage "wait and see" when a child is clearly behind.⁸

So if your baby has not done something on the list below by the age given, it is worth a conversation with your doctor. It does not mean something is wrong, but it should not be ignored. For babies born early, use corrected age.

What should my baby do by 2, 4 and 6 months?

By 2 months most babies smile when you talk to them and hold their head up on their tummy. By 6 months most laugh, roll from tummy to back, and reach for toys.⁹

• 2 months: smiles when you smile or talk, looks at your face, reacts to loud sounds, holds head up during tummy time.⁹
• 4 months: coos, turns towards your voice, holds head steady when held, brings hands to mouth, holds a toy you put in her hand.⁹
• 6 months: laughs, knows familiar people, takes turns making sounds with you, rolls from tummy to back, reaches for a toy, leans on her hands when sitting.⁹

What should my baby do by 9 and 12 months?

By 9 months most babies sit without support and babble "mamama" or "bababa". By 12 months most wave bye-bye, call a parent "mama" or "dada" and pull up to stand.⁹

• 9 months: looks when you call her name, is shy with strangers, smiles at peekaboo, makes many sounds like "mamamama", lifts arms to be picked up, sits without support, passes things between hands.⁹
• 12 months: plays pat-a-cake, waves bye-bye, understands "no", picks up small things between thumb and finger, pulls to stand and walks holding furniture.⁹

Crawling is the most variable skill. Some babies shuffle on their bottom or go straight from sitting to walking. That is usually fine if other skills are on track.

When should my baby walk and talk?

By 15 months most children take a few steps alone and try one or two words besides "mama" and "dada". By 18 months most walk without holding on.⁹

• 15 months: takes a few steps, points to ask for something, tries one or two words.⁹
• 18 months: walks alone, points to show you something interesting, tries to say three or more words.⁹
• 2 years: says at least two words together, such as "more milk", points to things in a book, runs and kicks a ball.⁹

Children growing up with Bengali, Hindi and English at home are not delayed because of it. Talk to your baby in whichever language feels natural.

What are the red flags for developmental delay?

These signs need a developmental check now, not a wait-and-see approach:

• no smile when you smile at her by 2 to 3 months
• not following your face, or not startling to loud sounds
• a body that feels very stiff or very floppy
• no head control by 4 months
• not reaching for toys by 6 months, or not sitting alone by 9 months
• a strong preference for one hand before 12 months, which can mean weakness of the other side
• no babbling by 9 to 10 months, and no response to her name by 12 months
• no pointing or waving by 12 to 15 months
• no words by 16 to 18 months, or no two-word phrases by 2 years
• not walking by 18 months
• loss of any skill she once had⁹

Why is losing skills a warning sign?

A child who stops doing something she could do before, such as saying words, making eye contact or using her hands, needs to be seen promptly.⁹

Loss of skills can be a sign of autism, hearing loss, or a nerve or metabolic condition. In all of these, early assessment helps.

Autism can be diagnosed as early as 18 months, and there are treatments that can improve how a child functions.⁷ That is why the AAP advises autism screening at 18 and 24 months.⁷

My relatives say boys talk late. Should I wait?

No. Some late talkers do catch up, but nobody can tell in advance which ones will. A hearing test and a developmental check do no harm.

Dr Dutta hears "boys talk late" and "his cousin did not speak until three and is now an engineer" in clinic almost every week. Those stories are true for some children. But early help works best, and the AAP aims for problems to be picked up and treated early.⁶

If you are worried, trust that feeling and ask. Parents usually notice first.

Can screen time affect my baby's development?

The IAP advises no screen time at all for children under 2 years.¹⁰ For ages 2 to 5, it advises at most 1 hour a day, with an adult.¹⁰

Screens take the place of the talking, play and face-to-face time that build language.¹⁰ Dr Dutta sees more and more toddlers with slow speech who spend hours a day in front of a phone, often while being fed.

Video calls with grandparents are a sensible exception. For your baby's language, nothing beats the simple things: talk, sing, read and play with her every day.

When should I ask for a growth or development check?

See your paediatrician if:

• your baby has not regained birth weight by 3 weeks⁴
• her weight is crossing lines downwards on the chart⁴
• her head seems unusually large or small, or is growing fast
• she shows any red flag in this post
• she has lost a skill she had⁹
• you feel something is not right, even if you cannot say what

Babies who were born very early, needed NICU care, had fits as newborns, or had very high jaundice should have planned developmental follow-up even if all seems well.