A child born of a teenage father is more likely to have problems at birth ranging from pre-term delivery and low birth weight, according to a Canadian study published Thursday.
The same newborn is also at greater risk of dying, says the massive study, which examined data for more than 2.6 million live births in the United States between 1995 and 2000.
At the other end of the age spectrum, researchers found that older fathers, 40 and over, posed no additional risk of these problems occurring.
Taken together, these findings -- which held true independent of other factors such as the age or health of the mother -- turn conventional wisdom on its head.
It has long been established that advanced maternal age increases the chances of foetal death and a whole range of health problems for newborns.
But the possibly adverse impact of paternal age on births has been relatively ignored, according to the study, published in Human Reproduction, an Oxford University Press journal.
In some cases, data is simply not available. In the United States, recent information on fathers, for example, is missing for 39 percent of unmarried women giving birth.
And earlier research that did link a host of problems at birth to older dads -- foetal death, spontaneous abortion, pre-eclampsia, heart defects, dyslexia -- may have been flawed due to small sample sizes or the failure to account for other factors, such as maternal age.
For the Canadian study, a team of researchers led by Professor Mark Walker of the University of Ottawa, looked at data for 2,614,966 babies born live in the United States to married women aged 20 to 29. Multiple births were excluded.
For each of these births, Walker and his team had access to complete information on the age and race of the father, prenatal care, and birth weight of the child.
Women in their twenties were the least likely to be affected by decreased fertility, which can create problems at birth.
The researchers found that babies born to teenage fathers were 15 percent more likely to be born early, 13 percent more likely to have a low birth weight and 22 percent more likely to die within four weeks of birth.
The danger of death doubled to 41 percent for the period between four weeks and one year old.
"The magnitude of the risks to society could be huge, given the numbers of births worldwide," said co-author Shi Wu Wen of Ottawa University.
Fathers 40 or older did not confer additional risk for their offspring for any of these criteria.
While the link between young fathers and problems at birth is clear, said Wen, the causes are less so.
"It is biologically plausible that paternal age might play a role in the risk of adverse birth outcomes," he said, pointing to previous studies showing that immature sperm may contribute to the abnormal formation of the placenta in the uterus.
But social factors probably play a role too, he added. Young fathers are more likely to come from poor families and to lack education, conditions associated with inadequate pre-natal care, drug use, smoking and alcohol abuse, he said.