Two new studies have revealed further evidence of the harmful effect of smoking on both male and female fertility. The first study found that prenatal exposure to maternal cigarette smoke reduces the number of germ cells and somatic cells in human embryonic testicles and ovaries.
Embryonic germ cells eventually form sperm in men and eggs in women, meaning a mother's smoking could influence the future fertility of her children. Equally, a reduction in the number of somatic cells in the testes could affect development of germ cells and functional sperm.
Although smoking during pregnancy has become less popular in industrialised countries during the last decade, one in eight mothers continues to smoke during their pregnancy.
Claus Yding Andersen, Professor of Human Reproductive Physiology at the University Hospital of Copenhagen (Denmark), and his colleagues studied 24 testes from embryos terminated between 37 and 68 days after conception. The embryos were taken from women aged 19-39 years whose smoking habits were monitored through questionnaires and urine samples. The researchers combined this work with past studies on 28 female embryos.
The number of germ cells was 55 per cent lower among male embryos from mothers who smoked compared to non-exposed embryos. Mothers' smoking also lowered the number of somatic cells in the embryos' testicles or ovaries. The effects were dose dependent with greater damage to germ and somatic cells found in embryos from the mothers who smoked the most.
These findings may potentially explain reduced fertility but the study, according to its authors: 'does not clarify whether the reduction in cell numbers (i.e. somatic and germ cells) is permanent or reflects a growth delay, which may be compensated for later in life'.
The second study, led by Professor Mohamed Hammadeh, Head of the Assisted Reproductive Laboratory in the Department of Obstetrics and Gynaecology at Saarland University (Germany), looked at the levels of two proteins believed essential for healthy sperm formation in the sperm of 53 heavy smokers (more than 20 a day) and 63 non-smokers. Deficiencies of the two proteins - protamines P1 and P2 - can led to infertility. Concentrations of P2 in the sperm of smokers was significantly lower than in non-smokers, leading to an abnormal P1/P2 ratio.
'In normal, fertile men, the ratio of P1 to P2 is almost equal at 1:1. Any increase or decrease in this ratio represents some kind of infertility', said Professor Hammadeh.
Both studies were published in the online journal Human Reproduction.