14 DAY TRIAL // It is said that younger parents deliver healthier babies. But this new research, so far the largest of its kind, and published in the journal Human Reproduction, shows that teenage fathers present a higher risk of having ill babies, the issues varying from pre-term delivery or low birth weight, to death in or near the time of delivery. Oppositely, older fathers, aged 40 and over, did not have a higher risk of unhealthy babies. This stood even when the age of the mother or other negative maternal factors were considered.
The team from the Ottawa Health Research Institute, Canada, employed data from the National Center for Health Statistics for almost all the births (99%) in the US between 1995-2000 (over 23.6 million). The researchers focused on 2,614,966 cases of singleton babies born alive to married women not having the first child, aged 20-29, where they could get complete data on paternal age, race, maternal education, prenatal care, and gestational and birth weight. That age category is the least affected by fertility issues, affecting babies' health. Fathers aged 20-29 are known to have the lowest risk of unhealthy babies, and this category was used as reference for other age groups.
The team adjusted the results for interfering factors (like race, education, smoking and alcohol drinking during pregnancy, prenatal care and the sex of the baby). Children born to teenage fathers (under 20) were more vulnerable to early birth (by 15%), low birth weight (by 13%), small gestational age (by 17%), low Apgar score (by 13%) or perinatal death (within the first 4 weeks after birth by 22% and 4 weeks to one year after birth by 41%), but, overall, the risk of death was under 0.5%. Fathers over 40 did not present a higher likelihood of these birth issues.
"Our study indicated that being a teenage father was an independent risk factor for adverse birth outcomes, whereas advanced paternal age was not. The paternal influence of younger fathers on adverse birth outcomes clearly warrants further investigation, and may lead to a deeper understanding of the causes of such outcomes. Although the increased relative risks for most outcomes were small, the magnitude of the risks to society could be huge, given the number of births worldwide, if the increases we found are truly attributable to paternal age," said co-author Shi Wu Wen, senior scientist at the Ottawa Health Research Institute and professor at the University of Ottawa.
The team classified fathers in seven age groups, from teenagers to those aged 50 and over.
"This, together with the large size of the study and the limited age range of the mothers, meant that the findings were unlikely to be affected by chance or confounding factors. However, there was no information available on the socio-economic status and lifestyle of the fathers, and this could have an impact. The mechanisms by which being a teenage father may contribute to an increased risk of adverse birth outcomes are not clear. Both biological and socio-economic status might play some roles in the observed findings," said Wen.
Younger men are known to present lower sperm counts, semen volume and percentage of motile sperm. Immature sperm are connected to birth issues, due to abnormal formation of the placenta in the womb. But social factors could also be involved.
"Young fathers are more likely to come from economically disadvantaged families and to have lower educational attainment. Socio-economic factors such as education and occupation are known to be associated with a number of health outcomes. People from less affluent backgrounds are less likely to utilize prenatal care services, which is associated with an increased risk of adverse birth outcomes. Other social factors that might play a role, perhaps by adversely affecting the mother's health, include domestic violence, lack of financial or emotional support, paternal illicit drug use, smoking and alcohol drinking. These are more prevalent in teenage fathers, and previous studies have found associations between paternal smoking and alcohol and adverse reproductive outcomes," said Wen.
On the other hand, "we did not find an association between older fathers and the increased risk of adverse birth outcomes. We could not exclude the possibility that older fathers who married women aged 20-29 years without childbearing history might have a higher socioeconomic status than our control groups. The advantaged socioeconomic conditions might offset some biological risk of adverse birth outcomes associated with older fathers," he added.