No improvement in semen quality despite decline in maternal smoking

A new study shows that the semen quality of young Danish men is still poor despite a marked decline in the proportion of men born by mothers who smoked during pregnancy. 


Poor semen quality in Danish men

Since 1996, Danish researchers at Department of Growth and Reproduction at Rigshospitalet in Copenhagen have been monitoring semen quality of Danish men. During the entire period, the semen quality has been poor. More than 6,000 men have had their semen quality examined, and in only 22% of the men, semen quality could be considered optimal based on the number of spermatozoa in the ejaculate, their motility and morphology.  In this study, semen quality is significantly lower compared to men examined in the 1940’s. Danish men are also among those with the lowest semen quality compared to other European countries. 

Prenatal life is crucial for semen quality

The potential for the man’s semen quality is already determined in the fetal phase, where the testicular development and future function can be disrupted by the pregnant woman’s lifestyle or exposure to environmental chemicals. A number of studies have shown that men exposed to maternal smoking during pregnancy have lower semen quality than other men. Accordingly, in the present study, the researchers observed that the men, whose mothers did not smoke during their pregnancy, had better semen quality. Therefore, it was a surprise that the semen quality overall did not improve between 1996 and 2016, despite the fact that significantly less men have been exposed prenatally to maternal smoking. In the beginning of the study period, 40% of men had been exposed to maternal smoking during pregnancy, while the number had dropped to 18% in most recent years.  

Need for more research

Niels Jørgensen, consultant doctor and principal investigator of the study, which was just published in the international scientific journal Human Reproduction, says:  

- We have not seen an improvement in the average semen quality of Danish men despite a rather large decrease in the proportion of young men exposed prenatally to maternal smoking. This indicates that other factors could be responsible for maintaining the current low quality, and it is crucial that we continue to investigate these factors to improve semen quality in the future.

More information

Contact: Consultant doctor Niels Jørgensen: Tel. 35 45 50 85

Or press consultant Linda Svenstrup Munk: Tel. 22 96 68 98  

Original paper

Read the paper at 

Priskorn L, Nordkap L, Bang AK, Krause M, Holmboe SA, Egeberg Palme DL, Winge SB, Mørup N, Carlsen E, Joensen UN, Blomberg Jensen M, Main KM, Juul A, Skakkebaek NE, Jensen TK and Jørgensen N. Average sperm count remains unchanged despite reduction in maternal smoking: Results from a large cross-sectional study with annual investigations over 21 years. Human Reproduction.

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