Álvaro Ruiz Zambrana and Begoña Olartecoetxea. PHOTO: Manuel Castells

Any dose of tobacco consumed daily decreases fertility in obese and overweight women, while in those of normal weight the chances of pregnancy are clearly reduced only after sixteen cigarettes a day. This is the result of a recent review of the literature on the epidemiology of fertility in the Clínica Universidad de Navarra on the epidemiology of fertility, which brings together the results of different international programs of study , both on natural and assisted reproduction.

This review, carried out by Dr. Alvaro Ruiz Zambrana with the participation of Dr. Begoña Olartecoetxea, specifies a series of modifiable lifestyle habits that favor fertility, such as maintaining a normal weight, avoiding the consumption of tobacco and alcohol, as well as learning to manage stress. "As a first measure, modifying certain habits can have good results and is especially indicated for those women who do not want to resort to artificial treatments for assisted reproduction. At final, the idea is to naturally increase the chances of becoming pregnant," explains Dr. Ruiz Zambrana.

In addition, these specialists of the department of Gynecology and Obstetrics of the University Clinic, emphasize the importance of knowing which are the fertile days within the menstrual cycle. "There are a series of biological indicators such as cervical mucus or body temperature that allow a woman to recognize, with minimal training, the fertile days. By directing sexual relations to those days, the probabilities of pregnancy increase", she specifies.

Pregnancy is delayed as body mass index increases

On the other hand, the fact of not maintaining a normal weight - a body mass index between 20 and 25 - decreases fertility in both obese and thin women. "Obese or overweight women and those who are excessively thin have fewer possibilities or it takes them longer to achieve pregnancy than those who have a normal weight," explains Dr. Zambrana. In this sense, he explains that "the higher the level of obesity, the longer it takes a woman to become pregnant. Thus, when the average time to get pregnant is around seven months, in obese women it can take up to eleven months".

In addition, the negative influence on fertility of overweight and obesity is worsened by smoking. "According to a study comparing fees fertility in women classified by weight and smoking, in thin women fertility clearly worsens only above sixteen cigarettes a day. However, in those who are overweight and obese, the fertility rate decreases from the first cigarette consumed", points out the specialist of Clínica Universidad de Navarra. This influence of smoking, he adds, "also occurs in passive smokers and in assisted reproduction, where the fees of implantation, pregnancy and 'take home baby' (healthy newborn) are reduced".
The results also show that cigarette consumption not only reduces fertility, but can also have a negative influence on the evolution of pregnancy. "A direct relationship has been observed between smoking and an increase in the issue of miscarriages during the first trimester, suggesting that smokers are more likely to suffer miscarriages than non-smokers."

Alcohol and excess caffeine worsen fertility

Another habit that can be modified when seeking pregnancy is alcohol consumption, according to Dr. Ruiz Zambrana: "Drinking more than five units of alcohol per week reduces the pregnancy rate per menstrual cycle. So the more alcohol consumed, the more difficult it is for a woman to become pregnant". One unit of alcohol is approximately equivalent to a glass of wine of about 100 milliliters or a can of beer of 200 milliliters.

Similarly, caffeine consumed in large doses appears to have an influence on fertility rate, according to the programs of study reviewed. "Although in itself caffeine is not bad, drinking more than 3 to 4 coffees a day has been found to decrease the chance of pregnancy by half."

Although it is difficult to measure, acknowledges the Clinic's specialist, a high level of stress also entails "more difficulties in getting pregnant and a higher issue of miscarriages".
On the other hand, Dr. Alvaro Ruiz Zambrana points out the woman's age as a determining factor that influences both fertility and the issue of miscarriages. "Maximum fertility is between 20 and 25 years of age; at 30 it already decreases by 15%, a percentage that drops between 26 and 46% at 35 years of age and falls to 95% between 40 and 45 years of age." On the other hand, the older you are, the greater the probability of miscarriages, due to the increase of genetic problems in the fetus. "At 30 years of age, the abortion rate ranges between 7 and 15%; between 35 and 39 it increases to 17 and 28% and, after 40 years of age, it reaches 34 and 52%."

He also points out that all the aforementioned habits - obesity, smoking, alcohol, caffeine and stress - can have an influence on the male reproductive capacity. "In the case of age, although it is a less determining factor for men, there is a decrease in fertility from about 45 years of age onwards".