Fertility refers to the natural ability to reproduce. In human females, fertility is the ability to conceive a child and, in males, the ability to impregnate a woman. Fertile men are able to father children, and fertile women can conceive when an egg is fertilized through sexual intercourse, resulting in pregnancy.
Age is the most important aspect of fertility in women. Fertility is highest when young women are in their late teens and early twenties. It diminishes gradually around age 30, and then declines rapidly between ages 35 and 40. Women aged 35 and older are 2.5 time more likely to have a stillbirth and also more likely to have a baby with birth defects or genetic abnormalities. At age 40, the chance of conception is only 5% in a given month, and the risk of miscarriage after conception is greater than the chance to have a live birth.
Fertility rates vary by country according to different factors that affect fertility. Demographic factors influence the number of children a woman has in her lifetime. Factors that increase fertility include:
Factors that may decrease fertility include:
The total fertility rate of a population is based on the average number of children born to a woman during her lifetime, assuming that she maintains an age-specific rate throughout the childbearing years and that she survives to the end of those years. Because these conditions are not absolutely certain, fertility rates represent an estimated trend and are not absolutely accurate. The fertility rate in the United States in 2015 was 2 children, decreased from 3.8 children in the late 1950s. In Europe, the average total fertility rate in 2015 was 1.58, with lower rates found in southern European countries, including Greece, Spain, and Italy; the rate of the former Yugoslavic state, Bosnia, was only 1.28, the lowest rate in all of Europe. Russia and the post-Soviet states were also low, averaging 1.54 in 2016. The total fertility rates of Asian countries are the lowest worldwide, with Japan at 1.45 in 2016 and Singapore and Macau below 1 in 2017. The lowest fertility rates in the world at any given time were in a city in China with a rate of 0.41 in 1990 and a rate of 0.80 for Eastern Germany in 1994.
Achieving a low birth rate can be a challenge for countries wishing to improve socioeconomic standards. Low-income and impoverished countries and regions in developed and undeveloped parts of the world tend to have high birth rates and high maternal and infant mortality. Africa has the world's highest fertility rate, and the World Health Organization is working with governments there to institute family planning that may help to encourage smaller families.
Racial and ethnic factors also influence fertility rates. In the United States, Hispanic and African American populations have higher fertility rates than other ethnic groups. In 2014, Hispanic births were 23% of one million U.S. births.
Understanding fertility is helpful for couples who wish to have offspring. A woman's monthly cycle begins with hormonal changes that promote ovulation, the release of an egg by the ovaries. Women are born with all the eggs they will ever have in their ovaries, and the eggs are released once a month during the childbearing years. The egg migrates from the ovary, through the fallopian tubes, and down to the uterus, or womb. The hormone progesterone is produced to help thicken the inner lining of the womb to prepare for the possibility of an egg being fertilized in the fallopian tube as it travels. An egg can be fertilized by sperm within 12 to 24 hours after it is released. Because sperm can survive within a woman's body for up to seven days, it is also possible for fertilization to occur even if sexual intercourse takes place before the egg is released. In the months an egg is not fertilized, the womb lining is shed and is discarded from the body with blood through the vagina. This process is called menstruation, or the menstrual period, or simply a “period.” The woman's monthly cycle lasts about 28 days, though it may differ between individuals. If a woman's menstrual cycle lasts 28 days and her period is regular (around day 14), then the fertile window will start on about day 10. A missed period in the next cycle usually, but not always, indicates pregnancy.
Fertility is the highest when young men and women are in their late teens and early twenties, a time when reproductive hormones and the sex drive are also high. This combination sometimes leads to unwanted pregnancies during the teen years and to high birth rates in many undeveloped parts of the world. Pregnancy rates for natural conception, or even after fertility treatment, decline dramatically between the ages of 35 and 40. Also, as a woman ages, her eggs age with her and diminish in quantity and quality. As a result, fertility may become a problem for some individuals who are beyond their teens and twenties and still desire to start a family. Fertility issues have been increasing since the middle of the twentieth century in developed countries mainly because more women tend to put off having families until after they have had an education, chosen a career, and worked to develop it. Rising rates of obesity and sexually transmitted diseases are also believed to be responsible for declining fertility in certain populations.
For most couples desiring to have a family, having regular and unprotected sex leads to pregnancy.
About 85% of couples in the developed world conceive naturally within a year, but one in six or seven couples may have difficulty conceiving. A couple may be diagnosed as infertile if a baby has not been conceived after trying for two years or more. Infertility may be caused by irregularities in the man or the woman, a combination of both, or sometimes for no apparent reason. No reason at all may be identified in up to 30% of cases of infertility.
The possibility of infertility in either a woman or a man is influenced by heredity, health status, and lifestyle factors. Female fertility is most influenced by age. As a woman ages, it will likely take longer to conceive and the risk of not being able to conceive increases. Risk of miscarriage and complications with pregnancy or delivery also increases. The father's age may also affect the chances of conception, the time to pregnancy, the risk of miscarriage, and the health of the child.
Common conditions that may affect a woman's fertility include:
Infertility in men may be the result of:
If a woman has missed a period and pregnancy is suspected, the first thing that is usually done is a pregnancy test to confirm that she has conceived. If a couple has tried to get pregnant for one to two years or more, tests may be done to check for fertility issues.
Doctors advise women under age 35 who wish to become pregnant and who have had regular sex with their partners for 12 months without birth control to undergo fertility testing. The doctor may first want to meet with the couple to find out about overall health and lifestyle factors, including their individual and family medical histories, medications taken, smoking and alcohol consumption or use of illicit drugs, and exposure to chemicals or radiation at home or work. The doctor also asks about the frequency of sexual relations, birth control history, sexual difficulties, and sexually transmitted diseases. After obtaining a thorough history, including the details of the woman's menstrual cycle, methods of birth control, and history of previous fertility testing, the doctor typically orders fertility testing for the woman and the man.
One of the first tests a doctor may order to evaluate fertility in a woman is a blood test to check the level of follicle-stimulating hormone (FSH), the hormone that triggers the release of an egg by the ovaries. A Pap smear may be done to detect abnormal cells in the cervix and rule out cervical cancer or sexually transmitted diseases that may interfere with conceiving. The hormone progesterone, which increases during ovulation, may be measured in a blood sample. Thyroid tests or other hormone tests may be done to rule out any condition that might interfere with ovulation. A series of x-rays may be done to examine the fallopian tubes and uterus (hysterosalpingogram). Transvaginal ultrasound may also be done to see images of the ovaries and uterus, looking especially for blockages or growths that may interfere with becoming pregnant.
A sperm count may be ordered from the man to check the numbers of sperm microscopically and their health and motility. The best chances of conceiving and having a health pregnancy occur when large numbers of sperm are good swimmers and the woman is younger than age 30 and healthy. If a sperm count is normal (15 million to 200 million per milliliter of semen), having regular sex will help to fertilize an egg that is released during ovulation, especially one to two days before ovulation is expected to occur. If much time has passed trying to become pregnant, sperm is one aspect of fertility that must be checked. If the sperm are the cause of infertility (less than 15 million per milliliter of semen), no treatments can correct poor sperm production or blockage of the sperm tubes (ejaculatory duct obstruction).
When planning to start a family, men and women are not usually thinking about fertility or the health of the male sperm or female eggs. If pregnancy has not happened within a reasonable amount of time and fertility testing has not uncovered any major health issues that would interfere with ovulation or conception, the doctor may advise boosting fertility through natural measures.
Improving fertility status may be a simple process of monitoring the woman's menstrual cycle. For example, ovulation can be monitored by checking body temperature. When an egg is released, progesterone increases to prepare the uterine lining for pregnancy, which raises body temperature slightly. A woman can take her temperature with a basal thermometer every morning before getting out of bed to help determine if she is ovulating. Even better, highly accurate ovulation kits are available that check the luteinizing hormone levels in urine to pinpoint the day of ovulation.
Besides monitoring ovulation, a woman's overall health status must be maintained, which includes watching her weight. If a woman is overweight or obese, losing weight may boost her chances of getting pregnant. Studies show that women who are overweight take twice as long to get pregnant as those of normal weight. Even a drop of 5% to 10% may improve ovulation and pregnancy rates.
Obesity in men may also cause infertility and low testosterone; being underweight may also cause infertility. Men can boost fertility by managing stress, maintaining appropriate weight, and keeping the testicles cool (i.e., avoiding hot baths, hot tubs, or saunas that tend to reduce the sperm count).
These study results helped to create the fertility diet, widely recommended to optimize fertility in women and couples, giving them the best chance for conceiving naturally. The ten steps of the fertility diet are described briefly as follows:
During pregnancy and even while trying to become pregnant, a woman is encouraged to take folic acid, other B vitamins, and vitamin D supplements, and to discuss with her obstetrician whether any other nutrients may need supplementation.
Men can help boost fertility by avoiding alcohol and tobacco, eating a diet high in zinc (found in meat, seafood, eggs, and whole grains), selenium (meat, seafood, mushrooms, cereals, and Brazil nuts), and vitamin E.
After a couple has consulted with fertility specialists to determine why they have not conceived, assisted reproductive technology (ART) may be recommended as an alternative option to natural conception. Reproductive technology is used primarily as treatment for infertility, but it is commonly referred to as fertility treatment.
In vitro fertilization (IVF) is the most common and most effective type of ART, providing treatments that involve a woman's egg and a man's sperm. Eggs are first removed from a woman's body and then mixed with sperm, to create embryos. The embryos are then placed back into the woman's uterus, simulating natural conception and pregnancy. Donor eggs, donor sperm, or previously frozen embryos may be used in IVF. A surrogate or gestational carrier may also be involved instead of the woman whose eggs were fertilized. The surrogate becomes pregnant with sperm from the male partner. A gestational carrier becomes pregnant using an egg from the female partner and sperm from the male partner.
The majority of couples wishing to start a family have normal fertility and conceive within a reasonable time. For those who do not conceive, various methods are available to help couples boost fertility. If this is not successful, other methods can be tried to correct infertility problems.
In addition to abstention and natural family planning, various methods can be used to prevent contraception, including condoms, diaphragms, contraceptive pills and shots, implants, intrauterine devices (IUDs), and morning-after pills. Sterilization is a permanent solution to preventing pregnancy.
See also Adult nutrition ; DHEA ; Fertility diet ; Folate ; Gestational diabetes ; Malnutrition ; Vitamin B6 ; Vitamin B12 ; Vitamin D .
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American College of Obstetrics and Gynecology (ACOG), 409 12th Street SW, Washington, DC, 20024-2188, (800) 673-8444, https:www.acog.org .
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Office of Dietary Supplements, National Institutes of Health, 6100 Executive Blvd., Rm. 3B01, MSC 7517, Bethesda, MD, 20892-7517, (301) 435-2920, Fax: (301) 480-1845, email@example.com, https://ods.od.nih.gov .
Society for Assisted Reproductive Technology (SART), 1209 Montgomery Hwy., Birmingham, AL, 35216-2809, (205) 978-5000, Fax: (205) 978-5018, firstname.lastname@example.org, https:www.sart.org .
L. Lee Culvert