The Apgar score, which was first created in 1952, rates the newborn on five parameters: respiratory effort, heart rate, reflex irritability, muscle tone, and skin color with a value of 0 to 2 (worst to best) for each. Thus, a total score of 10 is optimal. The score is calculated at 1 and 5 minutes after birth.

In the last few years, several reports have linked advanced paternal age with various adverse pregnancy outcomes, including fetal death and preterm birth. However, little was known about the impact, if any, on the physical condition of the infant at birth.

To investigate, Dr. Yuelian Sun, from the University of Aarhus in Denmark, and colleagues analyzed data from more than 70,000 couples who had a first infant born between 1980 and 1996.

The team reports in the research journal Epidemiology that, compared with fathers in their 20s, those between 45 and 49 years of age and those 50 years of age or older were 64 percent and 49 percent more likely, respectively, to have an infant with a 1-minute Apgar score between 1 and 3.

Moreover, fathers 45 years of age or older were at increased risk of having an infant with a 5-minute Apgar score of less than 7.

"The biologic link between advanced paternal age and low Apgar scores is unknown," Sun and colleagues say. However, some studies have shown that "expression of specific paternal genes is crucial for the placental development and that chromosomal aberrations tend to increase with paternal age."