New parents know all too well how rare a good night's sleep becomes after a baby arrives. Middle-of-the-night feedings and pre-dawn wake-ups take their toll. Now researchers have calculated just how great a toll it really is.

A recent study, published by Oxford University Press on behalf of the Sleep Research Society, found sleep satisfaction and duration sharply declined with childbirth, reaching the lowest point during the first three months after having a baby. And even six years later, parents' sleep still hadn't fully recovered.

Both sleep satisfaction and duration were much lower for new moms than for dads. Women saw an average sleep reduction of 62 minutes a night, compared to men, who got about 13 minutes less sleep, according to the study. Breastfeeding was associated with a slightly greater decrease in moms' sleep satisfaction.

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Six years after birth, moms still slept 20 minutes less and dads slept 15 minutes less than before the baby arrived.

"While having children is a major source of joy for most parents it is possible that increased demands and responsibilities associated with the role as a parent lead to shorter sleep and decreased sleep quality even up to 6 years after birth of the first child," study co-author Dr. Sakari Lemola, from the Department of Psychology at the University of Warwick, said in a press release.

Factors such as "age, household income, and dual vs. single parenting were unrelated, or only very weakly related, to improved sleep," the researchers wrote in the study.

So before you welcome that little bundle of joy, brace yourself: you may still be somewhat sleep deprived when they're in first grade.