Postnatal depression in fathers can have long-term consequences for the behavioural and emotional development of their child, research suggests.
Not only women suffer from postnatal depression
Bristol and Oxford University doctors found postnatal depression affects a significant number of fathers.
The Lancet study found baby boys whose fathers were depressed had twice as many behavioural and emotional problems in the pre-school years.
The researchers suggest health workers look for signs of paternal depression.
The researchers, working with colleagues from the University of Rochester in the US, analysed records on 8,430 fathers.
They found that eight weeks after the birth, 3.6% (303) appeared to be suffering from depression, with symptoms including anxiety, mood swings, irritability and feelings of hopelessness.
Oxford psychiatrist Dr Paul Ramchandani said: "We already know that postnatal depression in mothers can affect the quality of maternal care, and is associated with disturbances in children's later social, behavioural, psychological and physical development.
"While a significant number of men do report depression following the birth of a child, until now the influence of depression in fathers during the early years of a child's life has received scant attention."
Dr Ramchandani said there was research showing adolescent children of depressed fathers have higher rates of psychiatric disorder.
But he said until now very little was known about the effect of paternal depression on early child development.
The researchers assessed children at the age of three-and-a-half for signs of emotion problems, such as worry and sadness, and behavioural problems, such as hyperactivity.
There was a significantly higher rate of problems among boys whose fathers had been depressed early in their life, but girls seemed to be less affected.
Dr Ramchandani said: "It may be that boys are specifically sensitive to the effects of parenting by fathers, perhaps because of different involvement by fathers with their sons.
"The influence of fathers in very early childhood may have been under-estimated in the past, but these findings indicate that paternal depression has a specific and persisting impact on children's early behavioural and emotional development and that fathers influence their children's development from very early in life."
He said it was important that healthcare professionals looked for signs of depression in fathers - and offered treatment where necessary.
Professor Lorraine Sherr, an expert in the psychology of parenting at University College London, told the BBC News website the findings were not surprising.
She said her work suggested around 10% of new fathers suffered from depression.
"Antenatal care tends to be very woman-focused, but if fathers play a role in parenthood then they should be properly prepared too," she said.
"There is also very little recourse to services for fathers who are feeling depressed."