The results of a study on female mice might lead the way to improved treatments for human females experiencing certain reproductive difficulties. The study indicates that all female eggs are not alike throughout the female lifespan. The mice study suggests that there are two waves of egg development that makes girls eggs’ different from women’s eggs.

At the University of Gothenburg in Sweden, Professor Kui Liu and his research team discovered that the lab mice they were using created two distinct populations of eggs that were active at two distinct stages of reproductive maturity. Further research is needed to determine if this process occurs in all species of mammals, including humans.

The Liu findings indicate that the different eggs are produced from primordial follicles at different parts of the ovaries. According to Liu, some ovarian diseases begin with disorders in developing primordial follicles but there is limited physiological understanding of how primordial follicles develop.

Liu and his research team discovered that the first wave of follicular development begins at birth and continues until puberty. The eggs produced during this wave contribute to fertility from the onset of puberty to full maturity in adulthood.

The second wave of eggs is created in primordial follicles in the ovarian cortex. Once full maturity is attained, the eggs produced by these follicles gradually begin to replace the eggs produced during the first wave of production until egg development during the first wave stops completely. At this point, it is only the eggs from the second wave that remain available throughout the female’s reproductive years.

If the two-wave process is present in humans, the Liu findings could provide the first step to more precisely targeted development of treatments for infertility caused by ovarian diseases. By targeting the specific egg population affected by a disorder, Liu anticipates better therapeutic results.

One medical condition that might benefit from this study and cited specifically by Liu is premature ovarian failure (POF), a condition that affects between 1% to 4% of all women during reproductive years. The disorder is characterized by the loss of ovarian function before a woman reaches the age of 40. Symptoms of POF resemble those of natural menopause but are often more severe. The cause of POF remains unknown at this time.

Source: Liu, Kui, et al. “Two classes of ovarian primordial follicles exhibit distinct developmental dynamics and physiological functions (pdf).” Human Molecular Genetics. Oxford University Press. Jan 23, 2014. Web. Mar 13, 2014.