Smoking, confirmed a deleterious effect on fertility

Smoking is responsible for a delay in the time required to design, an increase in the frequency of infertility and a decrease in fertility from 10 to 20%, with a dose-response relationship, have warned Dr. Jacques Mouzon and Joëlle Belaisch-Allart (CHI Jean Rostand, Sèvres) at national meetings on the theme "Women and tobacco" which took place in Bordeaux (Bicetre, Kremlin Bicetre Hospital).

"Among couples who have sex without precautions, it is generally accepted that about 8 out of 10 years in the design and 9 out of 10 in 18 months. But this probability appears diminished by tobacco," reminiscent specialists reporting many studies have attempted to analyze this relationship.

Among them, a French study was conducted in 1986 with 1,887 volunteer couples belonging to the Mutual General of National Education (MGEN): the percentage of pregnancies a year has revealed 15% lower in smokers by compared to non-smokers (70% against 85%). Similarly, the study of the Oxford Family Planning Association, 6199 Research conducted on pregnancy objectified a doubling of the percentage of childless couples in smokers of more than 20 cigarettes, five years after stopping contraception, by compared to non-smokers.

In Denmark, a retrospective study of nearly 11,000 women showed that those who smoked 5-9 cigarettes per day were 1.8 times more likely than non-smokers to be more than 12 months to conceive. A second Danish study involving 423 couples followed after stopping contraception revealed not only a deleterious effect of smoking on women's fertility but also passive smoking in utero suffered this type of exposure is related a decrease in fertility to the offspring, even when the girl in turn of childbearing age, did not smoke then.

A European study (Germany, Denmark, Spain, France, Italy, Poland, Sweden), 64% of non-smoking women have achieved pregnancy within three months and a half, when they were only 53% of those smoking more than 10 cigarettes per day. In contrast, the percentage of women who took more than nine months to be pregnant from 19% to 28%. Women smoking more than 10 cigarettes per day, duration of infertility was 1.5 times on average, compared to non-smokers and the risk of infertility than 9.5 months in both 1.7 case. The duration of infertility has, again, been multiplied by 1.5 to 1.6.

A Canadian study of 2,607 pregnancies has established a significant decrease in fertility by 10%, even higher than cigarette consumption was high.

Finally, a British study showed on 8515 pregnancies, an increased risk of developing more than 6 months by 23% in smokers compared to non-smokers. The risk of developing more than one year increased by 54%. A second study showed on 1976 consecutive pregnancies, an increase in the time required to develop from 9.1 to 18.7 months among non-smokers and smokers of 15 or more cigarettes.

IMPACT ON THE QUALITY OF MENSTRUAL CYCLE

Smokers appear to have a frequency of dysmenorrhea (disorder rules) increased by 50% compared to non-smokers, especially as the number of cigarettes is high. One study even found a doubling of risk of dysmenorrhea in women smoking more than 10 cigarettes per day, the risk is multiplied by 3.4 for those who smoked for 9 years or more.

Smoking also appears to increase the duration of painful half-day average rules. In addition, smokers are more often irregular periods or shorter than non-smokers cycles. These disorders are reversible upon cessation.

A NEGATIVE EFFECT ON IVF

The impact of cigarette smoking on the outcome of in vitro fertilization (IVF) has been less studied and lower numbers. However, a study of 499 women showed a decrease in estradiol levels and the implementation in the group of smokers, while they were younger than non-smokers. The implantation rate was also found to be very less.

It has also been shown a decrease in estrogenic activity in smokers, both in blood and in the ovary during maturation. Researchers have found that one of the consequences of the action on the quality of ovarian stimulation was a decrease in the number of oocytes according to the number of cigarettes, 10 for non-smokers to 7.3 for women smoking more than 15 cigarette per day.

In addition, this reduction after infertility treatment could be estimated at 40% and has a dose-response relationship, the number of oocytes being smaller as cigarette consumption is highest.

Other authors also found a decrease in clinical pregnancy rates with the use of tobacco, especially from 10 cigarettes per day.

Finally, as in natural fertility, the action of the harmful tobacco appears on the course of pregnancy, with an increased rate of early miscarriages.

SEVERAL ASSUMPTIONS

"Several hypotheses have been advanced to explain the decline in fertility in smokers. The first involve the action of nicotine at the hypothalamic-pituitary axis, as suggested by the rise in the rate of early menopause in this type of women. Tobacco could therefore have an anti-estrogenic effect, "argue Drs Mouzon and Belaisch-Allart.

According to them, there are also arguments in favor of an altered metabolism of gonadotropins, which regulate the production of estrogen and progesterone and thus affect ovulation and implantation of the embryo, as well as maintaining of pregnancy.

"Nicotine, they say, seems to alter the release of gonadotropins, which may affect ovarian function. Components of cigarette smoke are also toxic to ovarian cancer in animals. Moreover, smoking affects metabolism male "sex hormones.

Other assumptions involve local action on the cervical mucus, tubal motility and ciliary function. "In IVF, the researchers observed a percentage of tubal infertility by 34% among non-smokers, 57% of former smokers and 62% among current smokers. Action tobacco may go through a change in the tubal function ", suggest experts.

Finally, they continue, the role of smoking on hypoxia and oxidative metabolism is increasingly studied. "This could go through the vasoconstrictor action of nicotine or more directly, by displacement of oxygen by carbon monoxide inhaled by smoking. This mechanism is also probably responsible for the increased incidence of stunting intrauterine growth retardation and in smokers, reducing oxygen supply to the fetus and placenta development, "they comment.