Female fertility, what is it and how is it studied?
Fertility is the ability to conceive within two years of unprotected intercourse. The fecundability of a normal couple has been estimated to be between 20% and 25%, although it is clear that the probability of conception drops over the first year to less than 10% after 7 cycles, and only 3% during the 12th cycle.
When it comes to fertility testing, the most important tests to determine female fertility are:
This measures the presence of the luteinising hormone, progesterone and prolactin, which are responsible for ovulation.
This is a technical X-ray that reveals the structural state of the uterus and fallopian tubes.
A test that determines the quality of eggs available for ovulation. Women over the age of 35 should consider this test as well as other complementary tests such as blood and imaging tests.
Detects conditions in the uterus and fallopian tubes.
Such as thyroid and pituitary hormones that control the reproductive process.
What are a woman’s fertile days?
The general length of the menstrual cycle is 21-35 days, counted from the first day of menstruation of the next menstrual period. In general, there are 6 days in a woman’s menstrual cycle when sexual intercourse can result in pregnancy: 5 days before ovulation and the day of ovulation are called the “fertile window”.
Phases of the menstrual cycle or ovarian cycle
The menstrual or ovarian cycle is divided into three phases:
- The follicular phase varies from 10 to 14 days in length, and is the phase that takes place before the egg is released.
- The ovulatory phase is the phase that occurs with the release of the egg. It lasts from 16 to 32 hours.
- The luteal phase occurs after the release of the egg, lasts about 14 days and ends with the onset of menstruation.
During each ovarian cycle about 20 ovarian follicles are released, normally only one follicle completes this process and is ovulated. Thereafter, the average chance of conception is about 20% per cycle. Only 30-50% of conceptions result in a live birth, and most are lost even before the next menstrual period.
Up what age a women is fertile
Generally speaking, women’s fecundability begins to decline from the age of 30 years and this decline accelerates from the age of 40 years. Chronological age is the major determinant of reproductive success in both spontaneous and assisted cycles, as it is a predictor of ovarian reserve.
How to increase fertility after 30 years old?
As we can see, all women experience a drastic reduction in fertility in their late thirties. Although the use of assisted reproductive technologies (ART) has increased in recent years, the incidence of infertility in this age group is still high.
Hence, much research has focused on identifying possible patterns to improve fertility rates after the age of 35-40.
Importance of nutrition in fertility
Nutritional factors have been the focus of much of this research. There is strong evidence that healthy preconception dietary patterns in both men and women of reproductive age have a beneficial effect on fertility.
In the Nurses’ Health Study (NHS) II, it was found that women who had the highest intake of a “fertility diet” consisting of plan-based vegetable protein, whole dairy foods, iron and monounsaturated fats during the preconception period has a 66% lower risk of infertility related to ovulatory disorders and a 27% lower risk of infertility from other causes.
Other factors such as age, body mass index (BMI), alcohol consumption, coffee consumption, smoking and oral contraceptive use were also controlled for in this study. Precisely from the above factors, a direct relationship between BMI and fertility was also concluded, with the risk of infertility being higher among those at the lower or higher extremes of BMI, i.e. those who were underweight, overweight or obese.
What are the risks of pregnancy after the age of 40?
This age, women over 36 or 40, is associated with a dramatically increased risk of infertility of fertility problems, miscarriage and births of babies with trisomy 21 (Down’s syndrome).
Infertility in women
The World Health Organisation (WHO) defines infertility as the inability to conceive after two years of regular unprotected intercourse.
Very few couples suffer from absolute infertility, which may result from irreversible, congenital or acquired loss of functional eggs or sperm, or form the absence of reproductive structures in either partner. With the advancement of fertility treatments and the availability of assisted reproductive techniques, such as in vitro fertilisation, the word “subfertility” is being used in favour of “infertility” or “sterility”.
Main causes of infertility in women
The causes of female infertility are classified as follows:
- Ovulation disorders: ovulation is rare or outright non-existent, caused by polycystic ovary syndrome, hormonal imbalances, ovarian insufficiency or excess prolactin.
- Tubal infertility: refers to damage to the fallopian tubes, a blockage that prevents sperm from reaching the egg or the fertilised egg from passing into the uterus.
- Endometriosis: occurs when the tissue that lines the inside of the uterus grows outside the uterus.
- Uterine causes: are those that interfere with the implantation of the egg or increase the risk of miscarriage, such as polyps.
- Infertility without apparent cause.
As mentioned above, a menstrual cycle lasts 21 to 35 days, and the fertile window is 6 days. So the rest of the cycle, approximately 22 days, would be considered the days of non-fertility, or lower probability of pregnancy than the fertile days.
What factors negatively affect a woman’s fertility?
Among the main factors that have a negative impact on female fertility are the following:
- Age, due to the fact that the quantity and quality of eggs decreases.
- Weight, both underweight and overweight or obesity affect ovulation.
- Sexual history, as sexually transmitted diseases (STDs) such as gonorrhoea or chlamydia can cause damage to the fallopian tubes.
- Alcohol, which reduces fertility.
- Smoking, which can damage the fallopian tubes and uterus.
What factors help a woman’s fertility?
Among the factors that naturally determine fertility in a woman are the following:
- Endocrine factors, defined by a correctly functioning menstrual cycle and ovulation.
- Fallopian tubes and uterus, defined by both correct structure and function.
- Endometrium, the quality of the mucus lining the uterus.
- Lifestyle, defined by diet, weight, and quantity and quality of sexual intercourse.
Foods that promote female fertility
As we have seen above, there is strong evidence for the link between fertility and nutrition. A balanced and healthy diet is the foundation for our body’s well-being and fertility. Foods to include for fertility include: green and yellow leafy vegetables, fruits, milk, seeds and legumes, lean meat, liver, fish high in unsaturated fats, oils high in Omegas (such as olive oil) and whole grains.
Vitamins and minerals related to female fertility
Adequate nutrition before and during pregnancy is important for optimising the health and well-being of both mother and baby.
Although many of the necessary nutrients are present in foods, physiological demands during preconception, pregnancy and lactation may require additional dietary supplementation.
Micronutrient deficiencies have been associated with significantly high reproductive risks, ranging from infertility to structural defects in the foetus.
Supplements for female fertility
Let’s look at some of the ingredients within food supplements that are useful for female fertility.
Folic acid and female fertility
Folic acid, a water-soluble B-complex vitamin, is necessary for DNA formation and cell division. It is a nutrient now recognised as important before and during pregnancy because of its proven preventive properties against neural tube defects.
Improving folic acid intake before pregnancy may reduce birth defects and maternal megaloblastic anaemia. EFSA recommends 250 micrograms/day of folic acid in adults over 18 years of age and in pregnant women. During the preconception period, an intake of 400 micrograms/day is recommended.
Omega 3 for female fertility
In women over 35 years of age, important changes in the metabolism of fatty acids begin to occur, which can affect the quantity and number of eggs. It is therefore important to ensure a good intake of Omegas 3, 6 and 9, especially Omegas 6 – GLA.
The EFSA recommends the following intake of Omegas in pregnant or conceiving women, in the following amounts:
- Intake 250 mg/day DHA and EPA + additionally 100-200 mg/day of DHA alone (Omega 3).
Regarding the amount of omegas ingested in the diet, the following percentages of Omega 3 and Omega 6 are recommended:
- Intake 0.5% of Alpha-linolenic acid (Omega 3) of total energy intake.
- Intake of 4% linoleic acid (Omega 6) of total energy intake.
Omega-3 and Polycystic Ovary Syndrome
In Polycystic Ovary Syndrome (PCOS), the use of Omega-3 has been shown to be useful. This syndrome is characterised by menstrual irregularity, insulin resistance, diabetes and obesity. In a meta-analysis of several studies involving 591 women with PCOS, taking Omega-3 for 12 weeks reduced both insulin resistance and blood lipid levels (triglycerides and cholesterol).
Peruvian Maca and fertility
Lepidium meyenii, also known as maca, is a Peruvian plant belonging to the Brassicaceae (Cruciferae) family. The reproductive benefits of maca have been attributed to it since ancient times due to its popular use. Many of these benefits have been scientifically proven.
With regard to the nutritional value of maca, its most important bioactive is glucosinolates, which have been shown to exert a positive effect on the reproductive area. Maca tubers also contain approximately 13-16% protein, a large amount of essential amino acids, polyunsaturated fatty acids, as well as high amounts of iron and calcium.
A 2016 study involving 175 participants demonstrated the benefits of maca on energy metabolism, mood and sexual desire. The generally used dose of maca is 1 gram/day and is intended for use by adults over the age of 18. It is not recommended for pregnant or breastfeeding women.
Vitamin B12, or cobalamin, is found exclusively in foods of animal origin. This vitamin is involved in the proper functioning of liver metabolism (homocysteine), as well as in the production of haemoglobin and the metabolism of fats and proteins.
Especially imbalances in homocysteine levels can affect fertility in terms of the quantity and quality of ovarian follicles as well as the quality of the embryo formed after fertilisation.
The EFSA recommended daily allowance for vitamin B12 in pregnant women is 4.5 micrograms. For the period before pregnancy the recommendation is 2.4 micrograms/day.
Vitamin D stimulates the production of reproductive hormones – progesterone, oestradiol and oestrone – which are involved in both ovulation and implantation of the fertilised egg in the endometrium.
This vitamin is also involved in the growth of uterine tissue, the production of the hormone chorionic gonadotropin (a marker and regulator of pregnancy) and the formation of the placenta.
Vitamin D intake in pregnant women is recommended by EFSA at a dose of 15 micrograms/day (600 IU/d). During the preconception period the recommendation is 5 micrograms per day.
Iron and calcium
Iron is of great importance to women at different stages. In relation to fertility, analysis of the Nurses’ Health Study II, a study of more than 116,000 women aged 24-42, showed that iron supplementation and non-heme iron from food can reduce the risk of ovulatory infertility.
“Iron deficiency and anaemia affect women more because they lose iron during menstruation and need more iron when they are pregnant or breastfeeding,” explains the Spanish Society of Haematology and Haemotherapy.
Calcium plays a relevant role in fertility, specifically during the preconception stage, as it participates in the ovulatory processes (luteal phase) and in the regulation of the hormones that control the reproductive process.
Calcium is determinant for bone development and maintenance, and this process is also associated with vitamin D, so any woman, whether preconception, pregnant or breastfeeding, should be advised on calcium intake.
The EFSA recommended intake of iron and calcium in pregnant women is 7-16 mg/day and 860-1000 mg/day, respectively. For preconception women the recommended intake is 750 mg calcium per day and 7 mg iron per day.
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