Depression during pregnancy is more likely to affect women who become mothers as teenagers or in their early 20s, according to a study.
And the children of women who become mothers between the ages of 16 to 22 are also more likely to have emotional problems and a lower than average IQ.
The South London Child Development Study showed this was particularly true if the mother was depressed during pregnancy, smoked when carrying the child or did not breastfeed.
The study, based at the Institute of Psychiatry, King's College London, looked at 176 families and recorded how a child developed during an 11-year period.
It found that 41.9% of teenage mothers had antenatal depression, compared to 35.7% of mothers in their early 20s and 18% of women in the group aged 23 to 38.
The research also found that 19.4% of children born to teenage mothers, 23.2% of children born to early 20s mothers and 9% of children born to older mothers had an emotional disorder at age 11.
Cerith Waters of Cardiff University, who presented the study's findings at a British Psychological Society conference at Alder Hey 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."