If you're a new parent, or will become one soon, it's very likely you have been told at length about how tired you'll be. It's very unlikely, however, you were told it could last up to six years. 

That's the result of a new survey announced today, as researchers tracking the sleep of thousands of men and women while their family size increased found that the amount of rest these parents get hits a low roughly three months after birth.

In news that will be unsurprising to the vast majority of mothers, this hits women the hardest.

What was surprising to even the researchers was the more permanent effect on sleep the survey found, as results showed sleep deprivation could last up to six years, with many parents not getting a "normal" night's sleep for many years. 

While women lose over an hour of sleep a night three months in, men lose just 13 minutes 

"We didn’t expect to find that, but we believe that there are certainly many changes in the responsibilities you have," Dr. Sakari Lemola, one of the authors of the research, at the University of Warwick, says, as quoted in the Irish Times

While crying newborns are the obvious causes for lack of sleep in the early months, as time goes on it is more varied events such as children who are sick or who have nightmares that keep parents awake, not to mention the overarching presence of stress that comes with parenthood. 

The study, which was published in the journal Sleep, collated data from adults in Germany who were surveyed through in-person interviews held once a year between 2008-2015. In these interviews, respondents were asked to rate their sleep quality on a scale from 0-10 and were asked about how many hours of sleep they got on a normal weekday and weekend day. 

The study specifically looked at the experiences of parents, with 2,500 women and almost 2,200 men reporting the birth of their first, second or third child during these interviews. To capture how these changes affected their lives, the researchers followed these respondents for up to six years. 

When it comes to motherhood, women reported that their sleep quality declined in the first year after the birth of their first child, dropping 1.7 points on the scale, while the decline after a second or third child was slightly less at just over 1 point. 

In practical terms, mothers reported a loss of 40 minutes of sleep per night, regardless of whether they were caring for their first, second or third child. 

But this is scant compared to the data from the three-month mark, which shows mothers lose just over an hour of sleep every night after birth compared to their sleep levels before pregnancy. 

This is compared to just 13 minutes of sleep lost for fathers during the same period. 

A mother is better able to adjust to sleep deprivation after one child, the study says

A notable discovery was that even four to six years after the birth of a first child, mothers still feel the affects of that dip in sleep quality, as overall sleep satisfaction was rated just over one point lower on average, while sleep duration is about 25 minutes less.

There is some good news, however, as mothers show their resiliency by adapting better to following births once the adjustment of the first is overcome. They reported that after the birth of a second child, sleep levels returned to levels of before that pregnancy, while after a third child they seem to bounce back. 

While the report has some limitations - being most self-monitored and interviews occurring once a year - it does ring painfully true for many women who have had children and spent more time trekking back and forth to the crib than their partners.