Women in the study ranged from 16 to 38 years old
Women who become mothers as teenagers or in their early 20s are more likely to suffer depression during pregnancy than older mothers, UK researchers say.
An 11-year study of 176 families found children born to women aged 16 to 22 are also more likely to have emotional problems and a lower than average IQ.
Researchers told a British Psychological Society conference more support was needed for "young mums".
The government said they were providing extra support for vulnerable parents.
The South London Child Development Study recruited from two GP practices in South London in 1986, when the mothers were pregnant with their first child.
Families were split into three groups, based on when the women had the child - 31 teenage mothers, aged 16 to 19, 56 mothers aged 20 to 22, and 89 older mothers, aged 23 to 38.
During the study the mothers and children undertook psychiatric and IQ tests with information also being included from school tests.
They found that 41.9% of teenage mums had antenatal depression, compared with 35.7% mothers in their early 20s and 18% of women in the group aged 23 to 38.
The research also found 19.4% of children born to teenage mothers had an emotional disorder at age 11 compared with 23.2% of children born to mothers in their early 20s and 9% of children born to older mothers.
Cerith Waters of Cardiff University, who presented the study's findings to delegates at the conference, held at Alder Hey Children's Hospital in Liverpool, said: "Young mums can be very vulnerable and it is clear from these results that they need much more support, not only after the birth, but before as well.
"Programmes aimed at helping young mothers need to be multifaceted, and they need to begin during pregnancy in order to address both the mothers and the child's needs."
A spokesman for the Department of Health said: "We recognise the importance of effective and early support for women with antenatal and postnatal depression.
"All professionals involved in the care of women immediately following childbirth need to be able to distinguish normal emotional and psychological changes from significant mental health problems, and to refer women for support according to their needs.
The Department for Children, Schools and Families said it would invest around £250 million over the next three years in local services for parents, particularly for those in challenging circumstances.
A spokesperson added that more than 2,500 Sure Start children's centres provide help to parents on early learning and childcare, parenting advice, health services and help finding work or training.