It can come as a huge shock for new parents when their sweet little baby suddenly refuses to sleep, frequently waking in the night and crying out for mum.
"Four month sleep regression" is a term used to describe this - somewhat distressing - parenting milestone, which according to leading American paediatrician and founder of Happiest Baby, Dr. Harvey Karp, is all connected to the ending of the fourth trimester.
The first twelve weeks of a baby's life is an intense adjustment to life outside the womb, and its similarly tough for a new mum as she gets used to the rhythm of parenting, learns about her child, and recovers from pregnancy and birth.
At the end of this period, the baby has hit an exciting new milestone, says Dr. Karp. 'What happens is that now the baby is awake to the world. By four months of age babies can do the most important thing you ever do for the rest of your life, which is develop interactive relationships. When you go, "hi, baby", they go, "ohhh" - they're responding to you. They're looking at you a newborn can't do that.'
And he says it is this new craving for interaction that plays in to a change in their sleeping patterns.
Dr. Karp, inventor of the SNOO bassinet, added: 'It's quite interesting, how much changes in those first four months. But because of that, when they wake up in the middle of the night, they want to play, they want social entertainment. By six months of age the brain has doubled in size, and they're much better able to regulate their sleep.'
Interestingly, Dr. Karp says that one common question that is often put to him by parents is "when should my baby start sleeping through the night?" - and his answer is 'never'.
He explained: 'It's a bit of a trick question. The answer is never. They never sleep through the night. Adults never sleep through the night, we all wake up or get into very light sleep two or three times a night. And if everything's okay, we fall back asleep. With children, it's the same thing, they get into light sleep and deep sleep. We all have these cycles of sleep.'
It was with this in mind that he designed the SNOO, which is designed to help get babies back to sleep. It's a system used from birth that combines swaddling, a gently rocking crib and white noise. These elements all combine to create womb-like conditions which help baby adjust to their new outside environment.
The SNOO Smart Sleeper Baby Cot counts celebrity fans including Beyonce, Gigi Hadid, Kate Hudson, Ashton Kutcher, royalty, as well as thousands of parents all over the world.
'The idea of the fourth trimester is that babies are not really ready for the world when they're born,' the expert told Women's Health. 'In the womb, they're held and rocked 24/7. So to put them in a flat still bed for 12 hours, is sensory deprivation for them. It's really strange, and they don't like it. They've never been on their back. It's strange for babies. It's not natural at all.
'You've taken away everything that they're used to for sleep, and suddenly you go, "well, why aren't they sleeping? Well, you just, it's like, you know, if I took away your bed, pillow mattress comforter, you could sleep on the floor, but you're not going to sleep well. And if we take everything away from the baby, they're not going to sleep well."'
The SNOO, which retails at £1,145, is designed to mimic the comforting, familiar motion that the baby developed in, and can keep the soothing rocking motion going 24/7 - even when parents are getting some much needed rest. Studies have revealed that the cots, which work out at costing a little over £6-a-day when used for the first six months of the baby's life can increase babies' nightly sleep by 1-2 hours.
Dr. Karp said: 'If you rock your baby to sleep, and you put them in a car, then when they get up at two in the morning, they go, "wait, where did you go, come be with me?" In a SNOO, when they wake up, they go back to sleep. If they're hungry they'll wake up all the way, but it's rather like an adult who is on a long aeroplane flight. You fall asleep and you wake up and you look around and you put your head back down. You fall back asleep again. The babies are a lot comfier.'
And while some parents are reluctant to invest in the futuristic cot as they fear their infant will become addicted to it, Dr. Karp says the opposite is true. 'The truth is they're born dependent on it, because they had it 24/7. By six months it's quite easy to gradually wean them off of the motion and the sounds.'
You Might Also Like