The simple answer to a complicated process is that ovulation is when a mature egg is released
from a woman’s ovary. The egg then travels through the fallopian tube where it waits to be
fertilized by sperm—and if that happens, it implants itself in the uterus, and a fetus begins to
However, before a mature egg can be released, a woman’s body goes through a series of
actions to prepare for this event. Multiple follicles (fluid-filled sacs) full of immature eggs grow
until a dominant one matures and releases estradiol (one of the main estrogens), leading to a
surge in luteinizing hormone (LH). This causes the follicle to rupture, releasing the mature egg
down the fallopian tube where it waits to be fertilized. If fertilization does not occur, the egg
disintegrates within 12-24 hours and the uterine wall sheds triggering menstruation, and then
the monthly cycle repeats.
Generally, a woman ovulates around day 14 of a 28-day menstrual cycle, and ovulation occurs
within 12-36 hours of the LH surge, but every woman’s body is different, so exact timing can
vary. Typically, only one egg is released during ovulation, but if there are two, the result can
lead to fraternal twins (two separate eggs fertilized by two separate sperm).
There are ways to stimulate more egg production, especially during egg donors’ cycles, so that a
woman’s body ovulates all the eggs that have been developing in the follicles, making retrieval
As far as what time of the month a woman is most fertile, the exact moment of peak fertility
can be hard to pin down since each woman’s cycle varies, but experts say that chances of
conception are actually higher two days before ovulation, since if the sperm is already waiting
in the fallopian tube the second the egg is released, it can be much easier to fertilize. However,
if fertilization does not occur within 12-24 hours, the egg disintegrates before the uterine lining
is flushed out during the next menstrual cycle.
In terms of general fertility, women are born with all the eggs they will ever have. At puberty,
the number can range anywhere from 300,000 to 400,000. As a woman ages, her number of
available eggs declines steadily until menopause, which usually starts by age 50.
A woman in her early 20s has around 200,000 eggs and her reproductive system is at its peak,
which is why it’s generally considered the best time to have a child—and also why egg donors
ages usually range between 21 to 30 years old—but that isn’t the only criteria used to
determine a good egg donor.
Once a woman reaches her mid-30s, the number of eggs drops dramatically, and even more so
in her 40s, which is often when infertility sets in. At this point, women who still want to
conceive may have to seek information on infertility treatments, which can include fertility
drugs, surgery, intrauterine insemination, in vitro fertilization as well as donor eggs and