A Baby Not Gaining Weight

When to get help

Call emergency services or seek urgent advice — 999 or NHS 111 in the UK, 112 or your GP out-of-hours service in Ireland, 911 or your paediatrician in the US and Canada, 000 or healthdirect on 1800 022 222 in Australia, 111 or Healthline on 0800 611 116 in New Zealand — if a baby who is not gaining weight is also floppy, hard to wake, has far fewer wet nappies than usual, has a sunken soft spot, or is vomiting forcefully after feeds. Those are dehydration and obstruction questions, and they outrank the growth question.

Arrange a prompt appointment with a GP, health visitor, public health nurse or paediatrician if:

• Your baby has not regained their birth weight by about two weeks of age.
• Your baby is losing weight at any point after the first few days.
• Weight has crossed downwards through centile lines on the chart, using the thresholds below.
• Your baby seems constantly hungry, or conversely has little interest in feeding.
• Feeding takes an hour every time, or your baby falls asleep after a few minutes at every feed.

The NICE thresholds

NICE guideline NG75 gives specific thresholds for concern about faltering growth, and they depend on where your baby started. A centile space is the gap between two adjacent lines on the UK-WHO growth charts. NICE suggests using as thresholds for concern:

• a fall across one or more weight centile spaces, if birth weight was below the 9th centile;
• a fall across two or more weight centile spaces, if birth weight was between the 9th and 91st centiles;
• a fall across three or more weight centile spaces, if birth weight was above the 91st centile;
• when current weight is below the 2nd centile for age, whatever the birth weight.

Notice what that framework does. A baby who was born small is allowed less downward drift before it counts, and a baby born large is allowed more, because settling onto a lower line after a large birth weight is common and usually normal. This is why one weight taken in isolation, and compared with a friend's baby, tells you close to nothing.

Weight loss in the first days is expected

Newborns lose weight in the first days as they pass meconium and lose fluid. Most regain birth weight by around two weeks. Losing more than about a tenth of birth weight, or not regaining it by two weeks, is the standard trigger for a feeding assessment rather than reassurance.

After that, growth is fastest in the early months and then slows. The AAP describes weight gain slowing noticeably in the second half of the first year as babies become more active, which surprises parents who expect the early rate to continue. A flatter line at nine months is often normal; a flat line at nine weeks is not.

How weighing should be done

Weigh naked, on the same scales, and plot on the growth chart in the personal child health record. The NHS advises against weighing too often: after the first two weeks, once a month up to six months is usually enough, then less frequently. Weighing weekly generates noise, not information, because normal variation between nappies and feeds is larger than the real weekly gain.

Ask for the plotted chart rather than a number. The shape of the line over time is the whole point, and a single figure without a chart cannot be interpreted by anyone, including a clinician.

What gets looked at first

In most babies who are not gaining, the answer is about intake rather than about disease, so a feeding assessment comes first. For a breastfed baby that means watching a whole feed: positioning, attachment, whether your baby is actually transferring milk, how often they feed, whether they are being woken for feeds, and whether tongue movement is restricted. For a bottle-fed baby it means how much is offered, how often, how the bottle is made up, teat flow and whether feeds are being finished.

Simple things fix a large proportion of cases: more frequent feeds, waking a sleepy baby, better attachment, longer feeds on one side before switching, or stopping a well-meaning routine that is spacing feeds too far apart.

The medical causes worth naming

If intake looks adequate, the question becomes whether milk is being lost or not absorbed, or whether demand is unusually high. Reflux with frequent large vomits, cows' milk protein allergy, a urine infection, coeliac disease once gluten has been introduced, cystic fibrosis, a heart condition that makes feeding hard work, and an overactive or underactive thyroid all appear on the list.

Expect the history and examination to do most of the work. Tests are directed by what is found rather than fired off as a panel, and a baby who is feeding well, developing normally and simply tracking a lower line often needs monitoring rather than investigation.

What not to do

Do not add cereal, rusk or anything else to a bottle to increase calories, and do not make formula stronger than the instructions say — concentrated formula is dangerous for a baby's kidneys. Do not start solids before around six months in an attempt to boost weight; solids at that stage usually displace milk, which is more calorific. Do not switch formula brands repeatedly in search of one that works.

Do not stop breastfeeding on the assumption that supply is the problem without a proper assessment. And do not weigh daily. If you find yourself doing it, hand the scales to someone else for a fortnight.

What to bring

Bring the red book or equivalent with all previous weights, a two or three day feed log with times and amounts, and a count of wet and dirty nappies. If you can, film a typical feed from the side. Those three things together usually answer the question in one appointment.