Midwives need more training to help them identify mental health issues with expectant and new mothers, a study has concluded.
Registered nurse and Massey University master's student Kristina Paterson says there are gaps in midwives' knowledge and practice regarding perinatal depression and anxiety.
Her research has been released by lobby group Maternal Care Action Group, which has a petition calling for increased funding and resources in this year's budget to address the issue.
Ms Paterson analysed the results of a survey last year by the charity Mothers' Helpers.
The results showed 63 percent of respondents had depressive symptoms that began during pregnancy, but more than two-thirds were not diagnosed until after baby was born.
Also, 96 percent of the women polled had risk factors for post-natal depression, but 72 percent weren't assessed for depression or anxiety by their midwife during or after pregnancy.
Ms Paterson says it wasn't the attitudes of midwives that contributed to gaps in screening and referring women for help, but knowledge.
"Midwives may be the only skilled health professional a woman comes in contact with during pregnancy and after birth," she said.
"If a midwife is struggling with workload and poor working conditions and has not been adequately resourced with the knowledge and practice skills to identify a woman needing help or further assessment for symptoms of depression, it is likely that the woman's diagnosis will be significantly delayed."
She said that, if depression or anxiety wasn't picked up early in the perinatal phase and went untreated, the impact on the entire family was significant.