The survey, which has been carried out for the seventh time, featured 126 NHS trusts.
Of those questioned, 12 per cent of the women said they were not told they may experience a change to their mental health after giving birth.
Just under two thirds of the respondents said they were “definitely” informed about how their mental wellbeing may be affected, while a quarter said this information was only communicated “to some extent”.
The majority (80 per cent) of the survey’s participants said they were told how to access mental health support after giving birth should they need it. However, a fifth of the women said otherwise.
Nigel Acheson, deputy chief inspector of hospitals and maternity lead at the CQC, said it is "disappointing" that women's postnatal experiences "continue to fall short, particularly in regard to women's mental health needs".
"While most women surveyed were being asked about their mental wellbeing, a significant proportion felt the quality of information they received could be improved," said Mr Acheson.
"It is absolutely right that the provision of specialist mental health services for pregnant women and new mothers has been recognised as a priority in the NHS long term plan and we hope to see the impact of this extended support in next year's survey results."
In addition to providing information about their knowledge of mental health support services, the women who took part in the study also shared how they felt towards the midwives who took care of them.
More than 80 per cent said they felt their midwives always listened to them, while a similar number said they were given "appropriate advice" when they first went into labour and that their midwives "always" respected their decisions with regards to how they wished to feed their babies.
The Royal College of Midwives (RCM) said it was "particularly pleased" to hear that the majority of mothers felt they had been listened to but expressed concern about those who had been "let down by the accessibility of postnatal care".
"Continuity of carer is crucial to ensure pregnant women receive safe and high-quality care, but we must have enough midwives to get this right," said Gill Walton, chief executive of the RCM.
"We will continue to work with NHS trusts and boards, and the relevant health departments, to ensure this is a priority."
Mr Walton added that while the RCM is aware that one in five women using maternity services "are affected by maternal mental health problems", there are "not enough specialist midwives to care for them".