Women suffering with antenatal depression need more support, according to the Royal College of Midwives.
The RCM made the comments after a new poll found that more than a third of women who suffer depression during pregnancy have suicidal thoughts.
Four in five mothers surveyed who suffered with depression in pregnancy went on to struggle with postnatal depression.
Half of the 260 women surveyed said their illness affected their relationship with their baby, according to the research conducted by the RCM and Netmums.
Cathy Warwick, chief executive of the RCM, said: "This survey shows that there is an urgent need to identify and help women with depression in pregnancy and after the birth of their baby. If we can identify women as early as possible then we could prevent them declining into much more serious mental health problems.
"The Government has made a promise to women that they will be offered better support postnatally and that more will be done to spot and support postnatal depression. However, we know that antenatal and postnatal services are suffering as a result of budget cuts and a shortage of midwives. This is in addition to the postcode lottery of service provision for women with postnatal depression.
"If this situation is not rectified, the NHS will continue to fail women with mental health problems during pregnancy or birth and the Government's pledge would be judged to be an empty promise."
Health minister Dr Dan Poulter said: "Pregnancy, and the birth of a new child can be both a joyous and an emotionally challenging time.
"The Government recognises that women with depression both during and after pregnancy need care and support, not stigma.
"That's why early diagnosis and support for women and parents is so important, and it is midwives who provide the vital personalised, one to one care for women and families during pregnancy and childbirth.
"That is why the Government has invested in over 900 additional midwives working in the NHS since 2010."