Let's start by understanding what it is.
Between 3-5 months of age, babies go from the newborn phases of sleep to the more adult-like sleep, which have "sleep cycles: of anything from 60 to 120 minutes during the night where your body quickly wakes to make sure you are safe. We adults are so used to this that we don't even notice, we out ourselves back to sleep quickly and effortlessly.
But this is what happens to our babies: if we put them to sleep by feeding or rocking in our arms and then place them in the bassinet, as we did up until this age with no problems, what happens now is that they wake up 1-2h later to check, and they suddenly see that their environment has completely changed, aka they don't feel safe, so they cry for us to come get them and place them where they should be, in our arms where they were before. This is why it's so important to make sure they fall asleep in the bassinet, and start before they get to this stage at 0-3months.
And this is what happens to us moms: when the baby wakes at night we assume they must be hungry, so we feed them and they fall back asleep. But they are now waking every 1-2h (more often than before) and so we think they are going through a growth sprout or something like that. This does not just happens once, it happens a bunch of nights in a row (weeks possibly) and then they get used to waking up frequently, which is the 4 month sleep regression.
To top it all, during this time babies become more aware of the world, which makes them more distracted during their day feedings, which makes them feed less quantity, but hey it's okay, because they are getting it at night, boom, this adds up to the night problem.
So here are the best tips you can do to help navigate through the 4 month sleep regression:
Understand what is happening.
Keep feeding often during the day, every 2-3h, and feed in a quiet area with few distractions.
Put baby down to sleep slightly awake at bedtime. I love to "pet" their forehead.
If baby was used to waking say 1am, 3am, and 5am like Beckham is doing, and suddenly wakes up every hour instead, don't feed the "new" wake hours, and instead try to gently help them put themselves to sleep.
Keep active during the day, with tons of developmental toys, activities, fresh air, vitamin D & fun. And keep a good the night routine with no stimulation and low lights before bed.
With all this said, I want to add that, when I had Sofia, I had read about the 4 month sleep regression, I had understood what it was, I had read about everything you could do to prep them to deal with it better, read all the things that parents swear by. And let me tell you, with Sofia, NOTHING WORKED.
Despite all of the above, she woke every hour, nothing helped her go back to sleep, she only wanted my arms despite having had fallen asleep on her own for the past three months, she woke up every single hour for 6 weeks straight, and never slept more than 2h after that until she turned two.
So I also want to add that: mamas, it is good to understand and be aware of these things, but also: all babies are different, live life, don't stress to much if nothing works, and enjoy the wild ride that's to come.
Good luck to us!