How do I know if my baby has a flat head?

That shape is usually described as a parallelogram. Gary Rogers, a craniofacial surgeon at Children's Hospital Boston, points out it is closer to a trapezoid, because the bulge at the front is never as pronounced as the flattening at the back.¹ His 2011 review in the Journal of Craniofacial Surgery is the reference point for this article, and the studies he draws on are listed at the end.

If someone has told you it is only cosmetic and your baby will grow out of it, and that did not sit right, you are not being precious. Parents often notice something early, are told to wait, and then want a clearer answer a few months on. Knowing what to look at turns a vague worry into a specific conversation.

Plagiocephaly comes from the Greek words for slanted and head, and Rogers is firm that the term only correctly describes flattening on one side.¹ Even flattening across the back is brachycephaly. A long narrow head, flattened down both sides, is scaphocephaly. Using one word for all three muddles shapes that behave differently.

All of them develop after birth from sustained pressure rather than from anything wrong with the skull. Where growth is resisted by a resting surface, the extra volume is displaced elsewhere, leaving a flat area with fullness around it. Baby flat head progression month by month covers what happens to the skull at each stage.

That flattening happens because of sustained pressure on one part of a fast-growing skull, which is exactly why where your baby rests matters day to day. The Perfect Noggin is a contoured head shaping surface that redistributes pressure away from flat spots, used alongside your physiotherapist's work if a neck imbalance turns out to be part of the picture.

Do this in good light, when your baby is calm and awake. It takes about two minutes. These are signs that may suggest positional flattening is developing. They are not a diagnosis, and none of them replaces an assessment by a health professional.

This is the most useful angle and almost nobody thinks to use it. Sit your baby on your lap facing away from you, or lay them on a changing mat, and look straight down at the crown.

Imagine a line from the middle of the forehead to the middle of the back of the head. The left half should look much like the right half. With plagiocephaly it does not. One side at the back is flattened and the whole head slants, so that side is effectively shorter from front to back. This is the trapezoid shape Rogers describes.¹

Still looking down from above, place an index finger just in front of each ear canal. In a typical head shape those two points sit level across the head. When one side at the back flattens, that whole side of the skull shifts forward and the ear moves with it. Rogers lists anterior displacement of the ear on the flattened side as a core feature, and it is one of the easier signs to spot because you are comparing two things that should match.

Now look at your baby face on, at their eye level. Rogers describes the facial pattern as a forward shift of the forehead, the ear and the cheek, all on the same side as the flattening. So the forehead on the flat side looks fuller and the cheek below it a little more prominent.

There is one more part to that pattern that is easy to misread. Because the cheekbone on the affected side moves forward, it reduces tension on the eyelid, and the eye on the flattened side often looks more open than the other. Rogers notes this is commonly mistaken for a droopy eyelid on the opposite side when nothing is wrong with that eyelid at all. If one of your baby's eyes looks wider than the other, check which side the flat spot is on before assuming it is an eye problem.

This is the sign that most often explains the other three, and Rogers treats it as the central one. Watch your baby over a day rather than in a single moment. Do they always sleep with their head turned the same way? When you call them from the other side, can they turn fully both ways, or does one direction stop short?

Fenton and Gaetani report a cervical muscle imbalance, usually called congenital muscular torticollis, in up to 70 to 95 per cent of infants with deformational plagiocephaly.¹¹ It develops when the head is held rotated and tilted in the womb long enough for one neck muscle to shorten and the opposite one to lengthen and weaken. His position is that a preferred head position should be treated as a cervical imbalance until a clinician has ruled it out.

Two practical points follow. The earliest sign is a head position preference, not a visible head tilt: your baby keeps returning to the same side however you reposition them. A tilt, when it appears, tends to show up later, usually around four to six months once your baby is holding their head up against gravity. Neck tightness needs a hands-on assessment from a paediatric physiotherapist, child and family health nurse or GP. Given how often it sits underneath a flat spot, a turning preference is a reason to book one rather than a reason to keep watching.

If the back of the head is flattened evenly across both sides rather than to one side, that is brachycephaly. The head looks wider and shorter from above, there is little rounding at the back, and it can look disproportionately broad from the front.

The correction Rogers makes here matters. Most babies with brachycephaly also have some one-sided asymmetry, and he describes that combination, asymmetric brachycephaly, as the most common deformational head shape of all.¹ So if your baby looks both broad at the back and slightly slanted, that is not two problems. It is the usual presentation.

Common, but not universal. Rogers notes fewer than a quarter of babies placed on their back develop visible flattening¹, and cites Hutchison and colleagues, who followed 200 New Zealand infants from birth, at 18 to 19.7 per cent.² In Australia the NSW Health guideline puts prevalence at 22.1 per cent at seven weeks, falling to 3.3 per cent by two years.⁷

Most are mild. That is genuine reassurance, and it is also not a reason to do nothing. Measured rates do fall as babies grow, but those measurements are ratios, so a head that gets bigger without the flat area changing still scores better, and the studies followed babies who were all receiving ordinary care with no untreated group to compare against. Nobody can tell you in advance what your baby's head will do. NSW Health notes there is strong evidence supporting early conservative management.

Not every unusual head shape is caused by position, and this is where home checking stops and professional assessment starts. Some are caused by the joins between the skull bones closing too early, a condition called craniosynostosis. That is not positional flattening, and it needs prompt medical assessment rather than home monitoring.

You do not need to push for a scan. Rogers notes a specialist can usually tell these conditions apart from history and examination.¹ When to seek medical assessment for your baby's head shape goes through the warning signs in more detail.

Almost certainly not. Rogers notes most term babies can hold their head up against gravity by around three months, and that further flattening after that age is unusual.¹ The skull grows fastest in the first four to six months, which is where changing how and where your baby's head rests has most effect. If you are at four months and nothing has shifted, get it assessed rather than give it more time. The 3 to 6 month window covers what is realistic at each age.

Book with your child and family health nurse or GP and ask specifically for a referral to a paediatric physiotherapist. Given how often a flat spot traces back to a neck that will not turn evenly, this is the step that matters most. A physio can measure the asymmetry, test neck rotation properly, and work out whether the issue is tightness on one side, weakness on the other, or both.

Meanwhile, photograph your baby's head from directly above every two weeks, in the same spot and the same light. Two photos four weeks apart give your physio something concrete to work from.

Keep supervised tummy time going daily, alternate which end of the cot you use, alternate which arm you feed from, and limit stretches in car seats, capsules and bouncers. Always place your baby on their back to sleep, in line with Red Nose Australia safe sleep guidance. What you can do at home for your baby's flat head sets all of this out step by step.