It is true that sleep disturbances happen at those approximate time frames, however, it is not simply due to the age of the child. These "regressions" are not age related, they are directly related to learning- and even more specific to learning the big skills- the milestones. Rolling, sitting, standing, walking, etc. These milestones tend to happen around the same relative age, and therefore, the sleep regression months came about.
We have been incredibly lucky in this house, in that when we enter one of these phases, it only impacts Caroline's naps and never her nighttime sleep. For some, it is the opposite, and for many it will disrupt both day and night sleep.
The way to identify that you are in a "regression" is by taking note of any new skills that are being learned. If you can tell that your baby has been focusing on learning something big, that is most likely the cause, and yes, you are in a "regression" or sleep disruption phase. If you do not see that your little one is focusing on learning new skills, you might be needing a schedule change instead.
Here are some resources that focus on identifying if you may need a schedule change.
If you have identified a skill that your little one is trying to master, however, and sleep of any sort has been disrupted, you can help your baby to move through this period by doing one simple thing: give them LOTS and LOTS of practice with that skill before naps and before bed.
For us, sleep disturbances have happened when learning the following skills : sitting, standing, and currently- walking. I woke up this morning and realized that every other time this has happened, I took my own advice and gave her lots of practice. This time, for some odd reason, I had forgotten to focus ALL of our attention on her new skill. We had been practicing, but not enough.
So, whether you call it a regression or a disturbance/disruption, one thing is for sure- sleep will be lacking and new skills will be learned. Help your baby master that skill, and you will be on the other side of this phase in no time.