How likely is pregnancy in 20s? 30s? 40s?

It may be believed that only the parts of the United States where sex education that involves scare tactics to promote abstinence until marriage (Hall 2016) results in adults with a poor understanding of contraception and reproduction (Rampell 2014), but actually, it’s a global problem. Women all over the world, have poor understanding of their fertility. Amy Klein, writer of the fertility diary for the New York Times wrote, “A global study published for World Fertility Awareness Month in 2006 surveyed 17,500 people (most of childbearing age) from 10 countries in Europe, Africa, the Middle East and South America, revealing very poor knowledge about fertility and the biology of reproduction,” (A. Klein 2015). 

Misconceptions set the stage for disappointment in adulthood when children are desired and a couple assumes that pregnancy will happen quickly and naturally. But the reality is that conception can only occur in a small window of time each month. Also, the likelihood of conception varies depending on the age of each partner, overall health and lifestyle, and other underlying medical conditions.


Although a woman’s age does not affect the fertile window itself, rather the likelihood of successful conception (Pfeifer 2016), many other age-related changes occur, including number and quality of eggs and chromosomal structure. For example, the incidence of clinically significant chromosomal abnormalities in live births dramatically increases with maternal age (ARSM N. Klein, MD), as shown in the table below:

Likelihood of Age Abnormality:

  • 1/500 under 30

  • 1/270 at 30

  • 1/80 at 35

  • 1/60 at 40

  • 1/20 at 45


Additional differences in female fertility are described by age group below. Male fertility, which is not addressed in this blog, also declines with age, but not as drastically as female fertility.


Under 30

Under 30 years of age is biologically considered the best time for pregnancy for women. This is when a woman has the highest number of good quality eggs and lowest risk for issues like ectopic pregnancies and birth defects (Watson 2018).


Although under 30 is when the female reproductive system is at its peak for bearing children, even during these prime fertile years, a woman only has a 20% chance of getting pregnant each month. In other words, 2 out of 10 women trying to conceive will get pregnant that first month. According to the results of a small study published in 2002, if a couple aged 26 or under has intercourse 2 days prior to ovulation, that will increase chances of conception up to 50%, while couples aged 27 to 34 have a 40% chance of conceiving with intercourse 2 days before ovulation (Graham 2002).


Having children under 30 years of age may be falling out of favor as more and more women are choosing to delay motherhood in favor of higher education and their careers (Sifferlin 2014) or as it has more recently been noted, having to wait until a mature partner comes along (Notkin 2017). Additionally, a woman’s 20s in today’s society may not be the best time in terms of the mother’s psychological health (Henig 2012) .


Ages 30 to 40

After age 30, even if a woman’s menstrual cycle remains regular, fertility drops due to age-related changes in the egg, uterus, and ovulation and hormone secretion (ARSM N. Klein, MD) . Dunson’s study found that, for couples aged 35, the probability of conception with sex 2 days before ovulation dropped to 30% versus their younger counterparts (Graham 2002).


Additionally, even if conception is successful, at age 35, women also have a 25% chance of having a miscarriage (Springen 2008).


For a 35-year-old who’s been trying to conceive for 3 months, the likelihood of conceiving in the following month is only 12%, and gradually decreases the longer she tries (Sozou 2012) .



Over 40

For a 40-year-old who’s been trying to conceive for 3 months, the likelihood of conceiving in the following month is only 7%, and gradually decreases the longer she tries with only 0.5% chance of conceiving in the next cycle after 3 years of trying to conceive (Sozou 2012) (American Society for Reproductive Medicine). On top of the decreased chance of conception, women over 40 have a 42% chance of having a miscarriage (Springen 2008) and a 1/500 chance of having a stillbirth (BBC 2013). One paper published in Royal College of Obstetricians and Gynecologists suggests inducing labor at 39 weeks for mothers in their 40s to prevent stillborns, particularly in the UK where they experience higher stillbirth rates than almost any high-income country (BBC 2013) .


In average women over the age 40, eggs show abnormalities, and women over 40 who have been diagnosed with infertility exhibit even more abnormalities than those not diagnosed with infertility. The embryos that are produced are less likely to implant, and the uterus also has decreased function as evidenced by age-related miscarriages, where the egg appeared normal. Plus, increased findings of dysfunctional labor, placenta previa (placenta in an abnormal position), or other uterine abnormalities, and endometrial polyps in older women also contribute to decreased fertility. Older women are also less responsive to fertility treatments like gonadotropins, and even at high levels, they produce less developing follicles and eggs (ARSM N. Klein, MD).

If you’re trying to conceive and you’re over 30, don’t lose hope! The results of a small study, published in Obstetrics & Gynecology in 2004 and headed by David Dunson, found that with sex at least twice a week, 82% of 35- to 39-year-old women conceive within a year, which is not too far behind the 86% of 27- to 34-year-olds (Twenge 2013). And while the number of eggs cannot be changed and it’s controversial in the Western Medicine world, there are several studies that show the quality of eggs may be improved by taking supplements containing myo-inositol, melatonin (Vitale 2016) and DHEA (Wiser 2010), which have been shown to help improve egg quality and ovarian function (APA). Always consult with your doctor before starting new supplements.


Of course, maintaining a healthy weight and lifestyle is recommended for everyone, but even more so for both partners when trying to conceive. Read more about how exercising can help with fertility here and other lifestyle factors that can affect chances of getting pregnant here.


Additionally, a study published in 2002 in Obstetrics & Gynecology asserted that the fertile window does not decrease with a woman’s age, but can decrease if the man’s sperm quality is reduced to the point where the sperm lives for a shorter amount of time inside the woman’s body (Dunson 2002).

According to the CDC, the birth rate for women aged 30-34 has risen steadily between 2012 and 2016, and the rate for those 35-39 has risen each year between 2011 and 2016. Even for women aged 40-44, live births have increased since 1982 (Hamilton 2018), so becoming a first-time mom well into your 30s -- and beyond! -- may not be easy or without risks, but it is not impossible.