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Anti-Mullerian Hormone (AMH) is produced by granulosa cells in small, growing follicles within the ovaries. The concentration of AMH in the bloodstream is strongly correlated with the number of developing follicles, making it a valuable marker for ovarian reserve. AMH levels are used to assess “functional ovarian reserve,” which reflects the pool of growing follicles that can potentially ovulate, rather than just the total number of follicles. Ovarian reserve refers to both the quantity and quality of follicles at any given time. Evaluating ovarian reserve is crucial for individuals at risk for diminished ovarian reserve (DOR), providing insight into reproductive potential.
Fertility & its age-related decline
Fertility is defined as the natural ability to conceive, typically measured by the fertility rate — the number of live births per 1,000 women. In demographic contexts, fertility is represented by the Total Fertility Rate (TFR), which estimates the total number of children a woman is likely to have in her lifetime. Female fertility is highly age-dependent, peaking in the early 20s and declining in the third and fourth decades of life. After age 35, fertility drops more sharply. Menopause, the natural cessation of reproductive ability, typically occurs in women between their late 40s and early 50s. As a result, women aged 35 and older are classified as being in “late reproductive age,” during which fertility significantly declines.
Causes of decreased fertility in
older women
Decreased fertility in older women results from several factors, categorised into two groups: oocyte-dependent and oocyte-independent causes.
Oocyte-dependent causes: Oocytes, or egg cells, undergo a series of transformations to become fertilisable eggs. The number and quality of oocytes decrease with age, beginning during foetal development when the oocyte pool is established. By 20 weeks of gestation, a female foetus will have around 6–7 million oocytes, but this number drops rapidly. At birth, only 1–2 million oocytes remain, and by puberty at age 13, around 3,00,000–5,00,000 oocytes are present. By perimenopause, only a few hundred oocytes remain, with only about 500 ever ovulating throughout a woman’s life. As the oocyte pool diminishes, women experience shorter cycles, menstrual irregularities, infertility, and eventually menopause. These changes begin around six years before menopause.
Oocyte-independent causes: Apart from the decline in oocyte quantity and quality, fertility is also affected by the health of the uterus, which is crucial for embryo implantation and placental development. While maternal age has a weaker correlation with stillbirth rates, it still influences pregnancy outcomes, even when accounting for factors like chromosomal abnormalities, obesity, and pre-eclampsia. Ageing also alters the microenvironment of the oocyte. Changes in gene expression related to angiogenesis (blood vessel formation) in cumulus cells surrounding the oocyte may contribute to this. Hypoxia (low oxygen) during oocyte maturation has also been proposed as a mechanism affecting chromosome segregation, further compromising fertility. Conditions such as uterine fibroids, endometriosis, and endometrial polyps, along with a dysfunctional endometrial response to hormonal stimulation, can also impact fertility.
AMH as a marker for fertility
As women age, their fertility declines, particularly after age 37–38, when the ovarian follicle pool depletes rapidly. IVF success rates show this decline: the live birth rate for women aged 40–42 is around 12.7%, which drops to 5.1% for women aged 43–44, and only 1.5% for those aged 45 and older. The success of Assisted Reproductive Technologies (ART) like IVF is influenced by multiple factors, but age and AMH concentration are among the most significant predictors. AMH is one of the best markers for assessing the age-related decline in ovarian reserve. It offers valuable information about the number and quality of a woman’s remaining follicles.
(The author is an obstetrics & gynaecology surgeon and a counsellor at the Army Wives Welfare Association.)