Suicide is the leading cause of maternal death in the UK. Mental health problems around pregnancy are thought to cost the country £8bn a year. And the impact on mothers and children can last for decades.
While he was Prime Minister, David Cameron promised to tackle this with a "revolution in mental health care", including targeted support for new mothers.
And Theresa May told the Conservative Party conference this autumn that she would use "all her power" to transform mental health services.
But BBC Reality Check wanted to know what action had there been to match the talk.
Maternal mental health care can be accessed by women from the beginning of their pregnancy through the first year of a baby's life.
Treatment for women who suffer from poor mental health during this time falls into two main categories:
- specialist services including inpatient care, for the most severely ill women
- more general services, including GPs, midwives and health visitors
In England, much of the focus has been on the first category - specialised mental health teams including psychiatrists, and mother-and-baby units for women needing to be admitted to a bed to receive inpatient care.
What's been promised?
In 2015, £365m was pledged to be spent over five years on specialist maternal mental health services in England.
The government also promised that 30,000 additional women would receive treatment by the year 2020-21.
Unusually, the money was ring-fenced within the NHS budget, meaning the health service had to spend it on this purpose.
And what's changed?
Since then, an extra 6,000 women have received maternal mental health treatment, which is ahead of the target.
Four new mother-and-baby units (MBUs) with eight beds each have been made available, as well as extra beds in existing MBUs.
Once the new units are fully up and running, the bed capacity for the most severely ill women in England will have increased by half.
And in the community, for women who don't need to be admitted to a bed, 20 new specialist services have been created covering 90 clinical commissioning group (CCG) areas around England.
CCGs are the NHS bodies responsible for organising health and care services for their local communities.
So the promises made in the past few years are beginning to materialise.
Psychiatrist and national director of perinatal mental health for NHS England, Dr Jo Black, says: "Over the last couple of years we've really started to see big progress is being made."
She acknowledges there is still more work to do, but says there is "lots to be really proud of" and she has seen the difference these changes are making to women's lives.
Help at home
But what about people who need support but don't fall into this most severe category?
While 0.2% of pregnant women and new mothers will experience postnatal psychosis or another chronic, serious mental illness, between 10% and 15% of women will suffer from mild to moderate depression or anxiety and 3% will suffer from post-traumatic stress disorder around their pregnancy and birth.
And most of these women will be looking for help and advice in the community - from their GP, midwife or health visitor.
But most GPs and midwives have not had specific training in mental health, let alone maternal mental health, according to Dr Alain Gregoire, who chairs the Maternal Mental Health Alliance, which campaigns for better care.
These services have not received any extra money for maternal mental health.
Health visitors generally receive better training in mental health, but since the responsibility for paying for them moved from the NHS to local councils in 2015, numbers have been falling.
And the sums of money promised are comparatively small.
The £365m is to be spent over five years, but researchers at the London School of Economics estimate the NHS would need to spend £337m a year to bring maternal mental health care up to the standard recommended by the National Institute for Clinical Excellence (NICE), the body that sets national health guidance.
So government is keeping its promises but, according to Dr Gregoire, the promises do not go far enough.
Around the UK
Healthcare is devolved and we're talking about England here. Campaigners had in the past often described the situation in England as a "postcode lottery", but provision in the other UK nations is even patchier.
In Wales there are two specialist maternal mental health care services but no mother-and-baby units.
Scotland has two mother-and-baby units.
And Northern Ireland has no specialist mental health services for new mothers at all, either inpatient or in the community.
You can find out more, watch highlights and get involved by going to bbc.co.uk/mumtakeover or search for #mumtakeover on social media