Data on reproductive outcomes derived from the Medical Birth Registry of Norway were linked with data on paternal occupation derived from the general population census. The study included the years 1976-2005. An expert panel categorized occupations according to exposure.

In the offspring of fathers most likely to have been exposed, a slight increase in risk was seen for preterm birth (OR = 1.08; 95% CI 1.03, 1.15). In this group there was also a decreased risk of cleft lip (OR 0.63; 95% CI 0.41, 0.97). In the medium exposed group there was increased risk for "other defects" and a decreased risk for "other syndromes" and upper gastrointestinal defects. There were many calculations carried out, and the number of statistically significant results is probably to be expected as a statistical "blip".

The main limitations of the study, as the authors admit, are the crude exposure classification, the crude information of other occupational exposures, and the lack of information on residential exposures. These probably led to misclassification, and a dilution of true relative risks.

The authors conclude:
            "This study is partly reassuring for occupationally exposed fathers".