How Age Affects Female Fertility: What to Know

How does fertility change through the reproductive years?

Fertility is highest in the early-to-mid 20s and begins a slow decline through the late 20s and early 30s that most people do not notice. The decline becomes more clinically meaningful in the mid-to-late 30s and accelerates significantly around age 37-38, with another threshold around 40. By the mid-40s, spontaneous conception is uncommon.

This pattern reflects two biological processes:

1. Declining egg quantity (ovarian reserve): The pool of eggs present at birth decreases continuously from puberty. AMH and antral follicle count — the main markers of ovarian reserve — fall throughout the reproductive years and drop more sharply in the late 30s and 40s. 2. Declining egg quality: As women age, the chromosomal segregation process that occurs during egg maturation becomes more error-prone. A higher proportion of eggs carry chromosomal abnormalities (aneuploidy), which leads to lower fertilization rates, lower implantation rates, and higher rates of early pregnancy loss.

What does 'advanced maternal age' mean and why does it matter?

The term 'advanced maternal age' (AMA) has traditionally been applied to pregnancy at age 35 or older. This threshold was originally set based on the age at which the risk of chromosomal conditions — most notably trisomy 21 (Down syndrome) — rises enough to warrant discussion of prenatal testing.

The term does not mean fertility ends at 35, nor does it mean pregnancy becomes dangerous — it is a clinical flag for more attentive monitoring and conversation about certain risks. Many people have healthy pregnancies and babies at 35, 38, and beyond.

How does egg quality affect pregnancy outcomes?

Chromosomal errors in eggs lead to embryos that either do not implant, stop developing early, or result in miscarriage. This is why:

• Miscarriage rates increase with age: The majority of early pregnancy losses are due to chromosomal abnormalities in the embryo. At 35, the miscarriage rate is meaningfully higher than at 25; at 40, it is higher still.
• IVF success rates fall with age: Because success depends on the proportion of retrieved eggs that develop into chromosomally normal embryos. This is why IVF success rate data is always reported by age.
• Preimplantation genetic testing (PGT-A) has become more commonly used in older patients — it identifies chromosomally normal embryos before transfer, improving the chances that a transfer leads to a viable pregnancy 1Ref 1Practice Committee of the American Society for Reproductive Medicine; Practice Committee of the Society for Assisted Reproductive Technology (2017).Guidance on the limits to the number of embryos to transfer: a committee opinion.PGT-A use in older IVF patients to select chromosomally normal embryos; age-stratified transfer guidelines.

AMH can estimate the egg pool remaining, but it cannot measure egg quality — that is inferred from age and, in IVF, from embryo development and PGT results.

When should I see a clinician if I am trying to conceive later?

Current guidance recommends:

• Under 35: Seek evaluation after 12 months of trying to conceive without success
• Age 35-39: Seek evaluation after 6 months
• Age 40 and older: Seek evaluation promptly — after 3 months or even before trying
• Any age with known risk factors (irregular cycles, history of PCOS, endometriosis, pelvic infection, prior pelvic surgery, or known male factor): earlier evaluation is appropriate regardless of age 2Ref 2Practice Committee of the American Society for Reproductive Medicine (2021).Fertility evaluation of infertile women: a committee opinion.Timing of fertility evaluation by age and presence of risk factors

Earlier evaluation does not mean rushed intervention — it simply provides more information so that decisions can be made with better data.

What options are available for people trying to conceive later?

Age is one factor among many, and it does not close doors — it changes probabilities and timelines. Available paths include:

• Timed natural conception with evaluation and supportive care
• Ovulation induction with monitoring
• IUI (intrauterine insemination) — a relatively low-intervention approach
• IVF — with or without PGT, potentially with higher medication doses to account for reduced ovarian response
• Egg donation — using eggs from a younger donor preserves the option of carrying and delivering a pregnancy even when a person's own eggs are no longer viable. IVF with donor eggs has high success rates relatively independent of recipient age.

The right path depends on individual circumstances, test results, partner factors, values, and timeline — a reproductive endocrinologist can model expected outcomes for your situation 1Ref 1Practice Committee of the American Society for Reproductive Medicine; Practice Committee of the Society for Assisted Reproductive Technology (2017).Guidance on the limits to the number of embryos to transfer: a committee opinion.PGT-A use in older IVF patients to select chromosomally normal embryos; age-stratified transfer guidelines.

Does male partner age matter too?

Yes, though the effect is more gradual. Sperm quality (motility, morphology, DNA fragmentation) does decline with male age, and paternal age has been associated with modestly elevated risks of certain genetic conditions and pregnancy loss. The biological urgency is less acute than for egg quality, but male age is not irrelevant in fertility planning — especially for men in their 40s and 50s 3Ref 3Schlegel PN, Sigman M, Collura B, De Jonge CJ, Eisenberg ML, Lamb DJ, Mulhall JP, Niederberger C, Sandlow JI, Sokol RZ, Spandorfer SD, Tanrikut C, Treadwell JR, Oristaglio JT, Zini A (2021).Diagnosis and Treatment of Infertility in Men: AUA/ASRM Guideline Part I.Male age effects on sperm quality and DNA fragmentation as a fertility factor.