Sleep Regression at 4, 8 or 18 Months: What Is Really Going On?

Your 4-month-old used to sleep six hours in a row. For a week now, they have been waking every two hours, and on the parenting forums the verdict is in: "it's the sleep regression". The phrase reassures, because it gives these hard nights a name and an end. It also worries, with its "regressions" announced at 8 months, 18 months, 2 years.

What do we really know about these phases? Less than social media claims, but enough to understand what is waking your child and to help you hold on.

"Sleep regression": what are we talking about?

The expression describes a period when a baby who was sleeping well starts waking often again, or refuses to fall asleep. It is mostly linked to 4 months, 8 to 10 months and 18 months.

It is not a medical term. The Quebec website Naître et grandir, reviewed by a neuropsychologist who specialises in children's sleep, does not use it on its page about baby sleep. It describes the same phenomenon differently: a baby's sleep does not progress in a straight line, and a baby who was sleeping several hours at a stretch can, without anything being wrong, start waking often again.

So the word "regression" is misleading. Your baby is not going backwards: their brain, body and emotions are changing fast, and their sleep follows those changes, with ups and downs.

What the science says (and what it does not)

American economist Emily Oster, who analyses studies on early childhood for her website ParentData, went looking for the famous 4-month regression. She does not find it in the data:

• a 2016 study based on data from a sleep-tracking app shows night-time sleep stretches getting longer throughout the first year, with no dip at 4 months;
• a large 2018 review concludes that night wakings decrease on average during the first year; parents report more wakings between 3 and 6 months, but sensors worn by the babies do not confirm it;
• in the same baby, night sleep can vary by about two hours from one night to the next.

Her conclusion: "regressions" are a poorly chosen name for normal variability in sleep.

The work of Marie-Hélène Pennestri's team at McGill University points the same way: nearly 400 infants were followed (Pediatrics, 2018). At 6 months, 38% of babies were not sleeping 6 hours in a row; at 12 months, 28% still were not. These babies were not developing any less well than the others. The researchers argue for better information for parents about this wide variability.

What science does not say, however, is that nothing is happening. Naître et grandir cites very real causes of disturbed nights: brain development, a virus, teething. The UK's NHS adds growth spurts and illness. And according to Naître et grandir, talking about a sleep disorder makes no sense before age 1: at that age, neither trouble falling asleep nor night wakings call for a diagnosis.

Around 4 months: sleep reorganises itself

This is the age when sleep changes structure. Between 3 and 6 months, according to Naître et grandir, sleep cycles lengthen from 50-60 minutes to 60-75 minutes, and your baby's wakings become easier and more frequent than before. Some babies sleep long at the start of the night, then wake more toward early morning. Three or four wakings a night are still normal at this age, as is needing to feed at night.

Growth spurts join in. Naître et grandir places them at around 1 to 3 weeks, 6 to 8 weeks, 3 months and 6 months: for 2 or 3 days, your baby wakes more often to feed. On those nights, answer their hunger; they pass quickly. The other changes of this age are described in our article on your baby at 4 months.

Around 8 to 10 months: separation anxiety arrives at night

Only yesterday your baby held out their arms to every visitor; today they scream as soon as you leave the room. Separation anxiety appears during the 8th month, sometimes between 6 and 9 months, according to Caf, and lasts a few weeks, sometimes a few months. For the MSD Manual, it generally starts around 8 months, peaks between 10 and 18 months and most often fades around age 2; it lists night wakings among its signs.

In the evening, falling asleep means leaving you. Naître et grandir notes that at bedtime as in the middle of the night, your baby may need reassurance. The same site lists other causes of waking at this age: teething, illness, a change of routine (holidays, Ramadan, a move), a parent going back to work. Between 6 and 12 months, three or four wakings a night remain the average.

The day prepares the night. Caf advises starting with short separations, telling your baby when you leave and when you come back, and playing peekaboo. It also suggests a transitional object, for example a handkerchief that carries your scent, for the moments without you. In the cot, however, nothing before age 1: the American Academy of Pediatrics (AAP) asks for a cot empty of any soft object, soft toys included, throughout the first year. Our article on 8-month separation anxiety goes into this stage in detail.

From the shop

For slightly more reassuring nights

No object shortens a difficult phase. A dim night light helps you step in without waking the whole house, and from age 1 a comforter can help your child cope with the evening separation.

• −35 %Safety 1stArctic automatic night light – Safety 1st150 DHinstead of 230 DHView product
• −9 %BadabulleAutomatic wall night light, pink Drops – Badabulle200 DHinstead of 220 DHView product
• −9 %DoomooYou&Me reversible comforter, Beige – Doomoo255 DHinstead of 280 DHView product
• −9 %DoomooYou&Me comforter with reversible head, Green – Doomoo255 DHinstead of 280 DHView product
• −48 %Doudou et CompagnieComforter doll with crib, pink – Doudou et Compagnie356 DHinstead of 690 DHView product
• −46 %BabymoovYOO-Travel video baby monitor – Babymoov1 394 DHinstead of 2 590 DHView product
• The whole aisle · Comforters17 products online, delivered anywhere in Morocco.Open the aisle

Products sold by La Maison du Bébé, publisher of this magazine. Prices as of 12 October 2026; please check the product page.

Around 18 months: separation, a changing nap and big emotions

The peak of separation anxiety, between 10 and 18 months according to the MSD Manual, coincides with other upheavals. The two naps, usual until about 18 months according to Naître et grandir, then shrink to one, and this change of rhythm often calls for a few adjustments. Our guidelines are in the article on baby naps.

The MSD Manual also describes tantrums, refusing to leave their parents' arms and stronger anxiety when the child is hungry or tired. It advises parents not to give up on separations, to stay calm and reassuring and to set up separation routines. The bedtime ritual plays exactly that role: see our ideas for a calmer bedtime. After age 1, a comforter can also join your child in bed and help with the evening separation: it is all explained in our article on the comforter.

How to get through these restless nights

A difficult phase does not mean changing everything. What helps, according to the sources cited:

1. Keep the bedtime ritual, even on holiday or at relatives' homes: the MSD Manual reminds us that separation routines ease a child's anxiety.
2. Respond quickly and calmly. Naître et grandir advises going to a baby who wakes, because they probably have a need, and staying in the dark: this is not the time to switch on the light or play. A low-light night light is enough to settle them again.
3. Look for a simple cause: hunger during a growth spurt, a blocked nose, fever, teeth, a room that is too hot or too cold.
4. Do not start a method where you space out your responses during these weeks. Naître et grandir reminds us that letting a baby cry does not help their sleep develop, and that such methods must never be used before 6 months.
5. Take turns. Every other night for each parent, or a morning off thanks to grandma, helps a lot. Our tips for keeping going are in the article on broken nights.