These same mothers who posted most frequently also reported stronger emotional reactions to comments on the photos they posted of their new baby - such as feeling bad if they did not get enough positive comments, researchers said.
The study looked at a specific group of moms - highly educated, mostly married women who had full-time jobs - and found that those who felt societal pressure to be perfect moms and who identified most strongly with their motherhood role posted more frequently than others to Facebook.
"If a mother is posting on Facebook to get affirmation that she is doing a good job and does not get all the 'likes' and positive comments she expects, that could be a problem. She may end up feeling worse," she said.
Those mothers who posted more on Facebook tended to report more depressive symptoms after nine months of parenthood than other moms, researchers said.
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Researchers studied 127 mothers from Ohio. When the women were in their third trimester of pregnancy, they measured how much they believed society expected them to be perfect parents.
They were asked to rate how much they agreed with statements like "only if I am a perfect parent will society consider me a good parent."
Nine months after the baby was born, researchers measured how much the women identified with their role as a mother.
Researchers also measured the frequency of their Facebook activity since their child was born, how often they uploaded photos of their children to Facebook and their emotional responses to friends' comments and likes of child photos.
Mothers who did make their child's image their own profile photos tended to show stronger identification with their mother role than women who did not, researchers said.
Moms also reported how often they felt depressive symptoms at three and nine months after giving birth.
The findings were published in the journal Sex Roles.