Ovarian follicles are small, fluid-filled sacs within the ovaries, each housing an immature egg. These follicles represent a woman’s finite lifetime supply of eggs, collectively known as the ovarian reserve. The number and quality of these follicles directly determine reproductive potential. Age is the most significant factor influencing this reserve, causing a predictable, continuous decline over time. Understanding the count of remaining follicles at a specific age, such as 43, provides a clearer picture of fertility status.
The Biology of Ovarian Aging
Females are born with their entire reserve of follicles, a supply that ranges from one to two million at birth. This number is fixed, meaning no new follicles or eggs are created after birth. The vast majority of this initial supply is composed of primordial follicles, which are the resting, smallest stage of the egg-containing sacs.
The continuous reduction in the number of follicles occurs through a process called atresia, a natural, programmed cell death that is largely independent of the menstrual cycle or ovulation. Atresia is not halted by pregnancy, hormonal contraceptives, or a healthy lifestyle; it is a constant biological mechanism. The supply drops to around 300,000 by puberty, with this steady loss continuing throughout the reproductive years.
The rate of follicle loss accelerates significantly after the age of 37. As a woman approaches her early forties, this decline becomes steep, marking a rapid depletion of the resting primordial follicle pool. This acceleration means that the total count of remaining follicles drops drastically in the years leading up to age 43, establishing a much smaller reserve.
Quantifying Follicle Count at Age 43
The total number of follicles at age 43, primarily composed of the non-measurable primordial follicles, is typically in the high hundreds to low thousands. This residual count is significantly diminished compared to the initial millions, representing the final stage before the complete depletion that characterizes menopause, which occurs when the count drops below approximately 1,000. While the primordial count indicates the total remaining life-long supply, a more clinically relevant number is the Antral Follicle Count (AFC).
The AFC represents the small follicles (2 to 10 millimeters in size) that are actively recruited in a given menstrual cycle and are visible via ultrasound. This number reflects the immediate, measurable ovarian reserve available for potential ovulation or retrieval. For a woman aged 41 to 45, the expected total AFC, summed across both ovaries, is typically very low, generally ranging from 4 to 10 follicles.
This low AFC is a direct consequence of the accelerated biological aging process. A count in this range indicates that fewer follicles are being recruited each month to begin the maturation process. A count near the lower end of this range suggests a diminished ovarian reserve, meaning the pool of eggs that can be accessed in any given cycle is quite small.
Clinical Assessment of Ovarian Reserve
Physicians rely on two primary measurements to estimate the ovarian reserve, which indirectly reflects the follicle count: the Antral Follicle Count (AFC) and the Anti-Müllerian Hormone (AMH) level. The AFC is obtained through a transvaginal ultrasound performed early in the menstrual cycle, providing an immediate snapshot of the number of small, fluid-filled sacs ready to respond to hormonal signals.
Anti-Müllerian Hormone (AMH) is a protein hormone produced by the granulosa cells within the developing follicles. It serves as a strong indicator of the size of the total resting follicle pool, including the primordial follicles not visible on ultrasound. AMH levels can be measured with a simple blood test at any point in the menstrual cycle, as they do not fluctuate significantly.
At age 43, the median AMH level often falls into a low range, sometimes around 0.81 nanograms per milliliter (ng/mL) or lower. A value below 1.0 ng/mL is often classified as diminished ovarian reserve, correlating directly with the low AFC seen on ultrasound. Follicle-Stimulating Hormone (FSH) is also sometimes checked as a secondary marker; a consistently elevated FSH level indicates the pituitary gland is working harder to stimulate a shrinking pool of remaining follicles.
Implications for Conception and Fertility Treatments
A low follicle count at age 43 presents a dual challenge for conception, impacting both the quantity and the quality of the eggs. The reduced number of follicles translates directly to fewer opportunities for natural conception each month. The lower AFC and AMH levels predict a poor response to the medications used in Assisted Reproductive Technology (ART) such as in vitro fertilization (IVF).
Ovarian stimulation for IVF aims to mature multiple follicles simultaneously, but a low reserve means fewer eggs will be retrieved, resulting in smaller numbers of embryos. Beyond the quantitative challenge, the remaining eggs in the diminished reserve are biologically older. This age-related factor leads to a higher rate of chromosomal abnormalities, or aneuploidy, in the eggs.
The combination of low quantity and reduced quality contributes to lower live birth rates associated with fertility treatments compared to younger age groups. While fertility treatments can optimize the chance of pregnancy with a small follicle pool, the diminished reserve means that success often relies on the quality of the few eggs that remain.