How does age affect fertility?

Diana Meeks
Diana Meeks on behalf of Sigma Nursing
Family Practitioner

As people get older, they are more likely to experience infertility. Aging affects the fertility of both men and women, but fertility problems may affect women at a younger age and with more extreme effects. Risks of infertility and pregnancy complications gradually increase after age 35 (including birth defects and miscarriage). This is because as women get older, their eggs also get older, and their bodies produce smaller amounts of sex hormones. Eventually, all women go through menopause (the naturally-occurring end of ovulation) and are no longer fertile.

Dr. Mark Perloe, MD
Fertility Specialist

This is an interesting question and addresses an area where much research is being carried out. The adverse effect of age does not appear to be mediated by a decrease in "fertilizability," but rather seems related to abnormal chromosomes in the egg.

Let's go back to review how the egg forms. All human cells other than sperm and egg normally have 46 chromosomes. The egg and sperm each contribute 23 chromosomes to the developing fetus. This means that as the egg and sperm are formed, the number of chromosomes needs to reduced to 23. This process of chromosome reduction is called meiosis.

In men, the process is ongoing, and new sperm are continually being produced. In the woman, the situation is a bit different. Before her birth, while she is still an embryo, the number of her eggs increases up to about 4-7 million. After about 20 weeks of gestation, her fetal body stops producing new eggs. These eggs must also undergo the process of meiosis to reduce from 46 to 23 chromosomes. But at 20 weeks, the eggs are surrounded by an envelope of cumulus cells; this arrests the meiotic process and keeps the eggs healthy until they're needed for ovulation. An egg resumes its growth about three months before ovulation. In fact, meiosis is not actually completed until after ovulation and fertilization has occurred.

We know that older women ovulate eggs that are more likely to contain chromosomal abnormalities, such as extra or missing chromosomes. What we don't know is when this anomaly occurs. Does it occur while the eggs are dormant, in a state of suspended animation awaiting their chance to grow and ovulate? Or does it occur after hormonal signals involved in ovulation stimulate the egg to resume meiosis?

Researchers have hypothesized that perhaps the cumulus cells surrounding the egg lose their ability over time to maintain healthy eggs. Some believe that chemical abnormalities within the cell are responsible for errors in chromosomal reduction (meiosis). At present, no means of restoring egg quality has been identified in women with age related fertility problems.

Dr. John K. Jain, MD
OBGYN (Obstetrician & Gynecologist)

A woman’s age is one of the most important predictors of fertility. Women have approximately 350,000 eggs at the time of puberty, (approximately age 13). Each month, during a woman’s menstrual cycle, dozens of these eggs will begin to develop, but only one will mature and actually ovulate. The remaining eggs will die and not be replaced. As a result, a woman’s overall egg pool diminishes each month. By the age of 30 a typical woman will have lost 88% of her overall egg pool. By age 40 the loss will have reached 97%. Despite these losses, monthly birth rates are well maintained through age 35. For example, every month, the chance of a woman’s egg developing into a pregnancy and ultimately a baby is 20% at age 25, and 15% at age 35. By the age of 40 that rate drops to 10% and by 45 to 2%. The reason for the rapid decline in birth rates beyond the age of 35 is not only due to lower egg counts but also decline in egg quality. Egg quality refers to the egg’s ability to create a chromosomally normal embryo. It is the egg and not the sperm that is responsible for early embryo development. Any mistake at this early stage, especially as it relates to chromosome segregation, will lead to an abnormal embryo that is likely to either die before forming a pregnancy or be miscarried by the 12th week of pregnancy. 

Dr. Jennifer A. Kalich, MD
OBGYN (Obstetrician & Gynecologist)

Biologically, fertility decreases with age. While women under age 30 have about a 20% per month chance of conceiving, only 5% of women over age 40 will conceive. Although women continue to have regular menstrual cycles until sometime near menopause, this doesn't necessarily mean they remain fertile. Regardless of the woman's cycle, fertility declines with the reduction in ovarian function and egg quality as women age.

Dr. Darria Gillespie, MD
Emergency Medicine Specialist

While age is indeed a factor in fertility, there is not a hard and fast age by which you must get pregnant. With new technologies, women are able to have children later and later with good outcomes.

A woman’s fertility does decline with age, though, particularly beginning in her mid-30s. Older age is associated with taking longer to get pregnant--your chances of becoming pregnant within a given cycle are lower after your mid-30s. That doesn’t mean it’s not possible, just that it may take longer. Many women develop other “comorbidities,” such as obesity and diabetes, that may lessen fertility, while the outlook may be different for a woman the same age who is otherwise healthy.

Also, as you get older, the risk of complications also increases, such as chromosomal abnormalities (like Down syndrome), preeclampsia and needing to have a C-section.

Age has a distinct effect on fertility. Hundreds of variables must coincide precisely for conception to occur and for a woman's body to successfully maintain a pregnancy for nine months. One study showed that the probability of pregnancy following intercourse on the most fertile day of their cycle in women with no fertility problems was 50% for women age 19 to 26, 40% for women age 27 to 34 and 30% for women age 35 to 39 when the male was about the same age.

If the male was at least five years older, the rates dropped to 45%, 40% and 15% respectively. Overall, 85-90% of couples having regular unprotected sex for a year will conceive.

Dr. Kevin W. Windom, MD
OBGYN (Obstetrician & Gynecologist)

That is an excellent answer. I would like to add that the miscarriage ratefor a 40 year old is aprox 50% and a 42 year old woman has a 75% chance of a miscarriage. A woman who is 35 or older should havs an AMH level to check to see how fertile she is and seek medical attention if she is not pregnant after 6 months of trying.

Dr. Evelyn Minaya, MD
OBGYN (Obstetrician & Gynecologist)

A woman's age can have a significant impact on fertility. That's because her eggs get older as she does. In this video, obstetrician and gynecologist Evelyn Minaya, M.D., discusses other ways in which age affects fertility.

Dr. Julia Schlam Edelman
OBGYN (Obstetrician & Gynecologist)

Fertility gradually declines for women in their thirties and continues to diminish until their fifties, depending on their personal biological schedule. Many women think that the signs of perimenopause mean that they are no longer fertile. In reality, fertility persists until postmenopause. Women in their forties have unplanned pregnancies at a rate second only to that of teenagers. Postmenopausal women cannot become pregnant. Perimenopausal women can and do.

Erika Tabke, MSN
Nursing Specialist

A woman's fertility declines by age. The older a woman is, the less likely she is to get pregnant each month. A woman is her most fertile before she is 25 years old. By age 25, fertility begins to decrease. Women in their twenties have a 20-25% chance of pregnancy each month. By 30, the chances of becoming pregnant are significantly smaller - at most, the likelihood of pregnancy is around 15%. By age 35, the likelihood of pregnancy in any given month is less than 10%. By the age of 40, most women will have difficulty getting pregnant without intervention.

Unlike a man whose body is continually making new sperm cells, a woman is born with all of the eggs she will ever have in her lifetime. As a woman ages, the percentage of eggs she has left (also known as her ovarian reserve) decreases. When a woman hits 30, she will only have about 12% of her eggs left. By age forty that number drops to a very small three percent.

If you are a woman under the age of 30 and are actively trying to conceive, you are urged to seek treatment after you have tried on your own for six to twelve months. If you are over thirty and are having trouble conceiving, do not wait more than six months to seek medical attention. Time is fertility.

Continue Learning about Infertility

What You Need to Know About Pregnancy After 35
What You Need to Know About Pregnancy After 35
At 50 years old, beloved pop legend Janet Jackson gave birth to son Eissa Al Mana. The singer made headlines not only because of her new baby, but als...
Read More
Is infertility just a woman's problem?
Honor Society of Nursing (STTI)Honor Society of Nursing (STTI)
No, infertility is not always a woman's problem. Both women and men can have problems that cause inf...
More Answers
Infertility Intervention
Infertility InterventionInfertility InterventionInfertility InterventionInfertility Intervention
Find out if you’re having infertility problems with this guide.
Start Slideshow
Does Infertility Run In Families?
Does Infertility Run In Families?

Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.