If you're a parent you may well be familiar with searching the internet for explanations for everything from sleep patterns to strange rashes – and one of the queries you might have run through a search engine is "When do babies stop crying so much?"
Up until now, the most authoritative study on the topic from 1962 has suggested that crying peaks at 6 weeks, before tailing off and stabilizing at a low level after 12 weeks – the generally accepted 'cry curve'.
Now a new study, encompassing a greater amount of data collected over a longer time, shows that sustained crying in infants can last much longer – and the team behind it wants to redraw the crying curve.
"If you Google 'infant crying' you'll see lots of images of this particular graph," says Arnault-Quentin Vermillet an instructor in cognitive science at Aarhus University in Denmark.
"Therefore, we thought it would be interesting to model all the available data to see what type of pattern best represents the data, and test if this is consistent with the original 'cry curve'."
The standard definition for excessive crying (colic) is to be crying for more than three hours per day, and for at least three days per week. In the first six weeks after birth, between 17-25 percent of babies are thought to be colic.
Here the team pulled together information from 17 different countries and 57 separate research projects, covering crying habits for a total of 7,580 infants, as reported by their parents. Importantly, the data covered 12 months, rather than the 12 weeks that the 1962 study dealt with.
While the data showed a lot of variability in terms of crying patterns, the researchers crunched the numbers to come up with two statistical models: one showing a crying peak after four weeks, and one showing a steady level of crying for the first weeks followed by a gradual reduction.
Neither model lines up all that well with the traditionally accepted cry curve, while the data also shows that excessive crying can often continue for months – which might be reassuring for new parents wondering about their babies.
"We've created two mathematical models that reasonably represent the available data," says neuroscientist Christine Parsons from Aarhus University.
"Neither of them show that the duration of crying falls so markedly after five weeks, which is what is otherwise seen in the graphs that are presented to parents. The available data shows that crying is still a significant part of many infants' repertoire after six months."
The researchers also noticed that crying habits can vary quite considerably between countries, although data is limited in some regions. For example, infant sobbing rates in India, Mexico, and South Korea are less than in countries such as the US, Great Britain, and Canada.
Crying is an important part of a child's development. It's used to get the attention of parents, and how the parents then react can be influential in terms of the infant's cognitive and emotional development.
As well as reassuring parents about what the norms might be in terms of crying patterns, the new research could also be helpful for healthcare professionals who are tasked with recognizing when something more serious could be happening.
"For clinicians in particular, it's important because their job is to help, support, and reconcile the expectations of any worried parents," says Parsons.
"It's important that clinicians have up-to-date data on what is normal for infant crying, so that they can best support new parents."
The research has been published in Child Development.