The effects of tobacco on fertility

In women, tobacco impairs fertility through various mechanisms. Nitric oxide (NO), nicotine and carbon dioxide produced by cigarettes cause hypoxia (poor oxygenation) of the various tissues, which will impair the proper functioning of the various organs (ovaries, fallopian tubes, uterus) involved in conception. Cigarettes also contain toxic substances that can lead to endocrine disruption, potentially harmful to fertility. Thus, it has now been shown that in women, smoking is responsible for :

ovulation disorders, by altering the production of oestrogen by the toxic products of tobacco (nicotine, tar, etc.) a decrease in the number of oocytes and a decrease in the ovarian reserve a decrease in the capacity of the oocytes to be fertilised (by thickening of the pellucid zone of the oocyte) a decrease in ciliary mobility (natural movement of the fallopian tubes) necessary for the migration of the gametes and the egg. The chances of the oocyte and spermatozoon meeting are therefore reduced and the risk of ectopic pregnancy increased. 20% of EPs are attributable to smoking (1). hypoxia, which alters the vascularisation of the uterus, leading to a reduction in the embryo’s ability to implant in the uterus. In the end, smoking is responsible for a drop in female fertility of between 10 and 40% depending on the number of cigarettes smoked per day. It also lengthens the time to conception by 4 to 6 months, bearing in mind that the more cigarettes smoked, the longer this time is (2).

The effects of tobacco on fertility

For women, tobacco impairs fertility through various mechanisms. Nitric oxide (NO), nicotine and carbon dioxide produced by cigarettes cause hypoxia (poor oxygenation) of the various tissues, which will impair the proper functioning of the various organs (ovaries, fallopian tubes, uterus) involved in conception. Cigarettes also contain toxic substances that can lead to endocrine disruption, potentially harmful to fertility. Thus, it has now been shown that in women, smoking is responsible for :

  • ovulation disorders, due to alteration of oestrogen production by toxic tobacco products (nicotine, tar, etc.)
  • a decrease in the number of oocytes and a decrease in the ovarian reserve
  • a decrease in the capacity of the oocytes to be fertilised (by thickening of the pellucid zone of the oocyte)
  • a decrease in ciliary mobility (natural movement of the fallopian tubes) necessary for the migration of the gametes and the egg. The chances of the oocyte and spermatozoon meeting are therefore reduced and the risk of ectopic pregnancy increased. 20% of EPs are attributable to smoking (1).
  • hypoxia, which alters the vascularisation of the uterus, leading to a reduction in the embryo’s ability to implant in the uterus.

In the end, smoking would be responsible for a drop in female fertility of around 10 to 40% depending on the number of cigarettes smoked per day. It also lengthens the time to conception by 4 to 6 months, knowing that the more cigarettes smoked, the longer the delay (2).

For men, recent studies have shown that certain substances in cigarette smoke pass the blood-testicular barrier and, once in the seminal fluid, lead to an alteration in sperm parameters and sperm quality, thereby compromising the chances of pregnancy (3).

The consequences of smoking on pregnancy

Smoking increases the risk of various pregnancy complications:

  • the risk of early miscarriage is multiplied by 1.5 to 3 depending on tobacco consumption. For a woman smoking more than 30 cigarettes a day at the beginning of pregnancy, this risk is multiplied by 5 (4).
  • the risk of low placental implantation which can cause a retroplacental haematoma and bleeding in the third trimester
  • the risk of rupture of the membranes before 34 weeks of amenorrhoea would be multiplied by 3.
  • leading cause of preterm delivery in pregnant smokers (5).

The effects of tobacco on the fetus

Smoking alters the development of the foetus through various mechanisms, the first being reduced oxygenation. When the mother-to-be smokes, her blood is charged with carbon monoxide, and the foetus is oxygenated by the mother’s blood; it is therefore directly exposed to this toxic gas. Moreover, nicotine has a vasoconstrictive effect on the arteries of the placenta and the umbilical artery. The maternal-fetal circulation is therefore less efficient and the fetus less well oxygenated. Finally, the toxic substances contained in cigarette smoke are directly harmful to the

baby’s development. Smoking also exposes the foetus to various complications:

low birth weight: smoking is the leading preventable cause of intrauterine growth retardation (IUGR). The more cigarettes smoked per day, the more this delay is increased. For every 10 cigarettes smoked per day, it is estimated that the baby’s weight is reduced by 200 g compared to a non-smoking mother-to-be (6)

  • an increased risk of foetal malformation
  • premature delivery

These effects are dose-dependent: the more the mother-to-be smokes, the greater the risk to the foetus.

After birth, smoking during pregnancy is responsible for the baby’s

a risk of sudden death multiplied by 2 (7)
an increase in respiratory problems (asthma, ear infections, pneumonia)

Treatment to stop smoking

It is advisable to stop smoking completely before becoming pregnant in order to optimise the chances of conception and to start a pregnancy without any tobacco contamination that could be harmful to the foetus and the pregnancy. According to specialists, the ideal is to wait for a cycle of cellular regeneration without tobacco; in this way the cells will not be exposed to the toxic molecules of tobacco. However, it is never too late to stop smoking, even once the pregnancy has started.

In pregnant women, psychological and behavioural approaches are preferred. Nicotine substitutes can be used in case of failure, but only under medical supervision. The Assurance Maladie covers the cost of these nicotine substitutes up to a maximum of 150 euros per year, subject to a doctor’s or midwife’s prescription.

The case of passive smoking

Passive smoking in utero also has consequences for the foetus and the course of the pregnancy. The substances contained in cigarette smoke are inhaled by the mother-to-be, pass into her bloodstream and thus into that of the foetus via the placenta, which does not filter all the chemical substances. A study (8) has thus revealed nicotine levels in the amniotic fluid of non-smoking pregnant women exposed to tobacco, as well as in the baby’s urine at birth.

A meta-analysis (9) showed that passive smoking by pregnant women was associated with lower birth weight, smaller head circumference and a greater risk of congenital anomalies.