The five basic elements necessary for pregnancy are all equally important and indispensable:

  • Healthy sperm
  • Healthy egg cells
  • Unobstructed fallopian tubes (where sperm meets the egg)
  • High-quality sperm that can fertilize the egg
  • A healthy embryo that can implant in the uterus

Egg Cells

An egg cell is the female reproductive cell, produced by the ovaries, and is the largest cell in the human body, with a spherical shape and a diameter of about 0.2 millimeters. During the middle of a woman’s menstrual cycle, a developed egg cell (referred to as a “secondary oocyte” by doctors at this stage) is slowly released from the ovary along with the follicular fluid.

The egg cell contributes half of the genetic material (DNA) to the offspring, meaning that half of the child’s traits—such as physical appearance—are determined by the mother who provides the egg.

The process of egg cell production is different from that of sperm. In the early stages of a female embryo’s development, while she is still in her mother’s womb, about 4 to 7 million oogonia (precursor cells to eggs) are produced in the ovaries through mitosis. By the sixth or seventh month of fetal development, these oogonia grow into primary oocytes and begin meiosis: DNA is replicated once, and the cell undergoes two divisions. However, the process pauses in the late prophase of the first meiotic division and remains in this stage for years, sometimes decades. Many oogonia do not make it to this stage and are naturally eliminated.

By the time a female is born, only about 500,000 primary oocytes remain, a significant reduction from the initial number. After further reductions during childhood, adolescence, and puberty, only about 100,000 primary oocytes are left by adulthood.

After reaching sexual maturity, a woman’s body awakens 10 to 20 primary oocytes each month, allowing them to resume meiosis. Typically, only one egg cell matures and is released during ovulation: the first meiotic division is completed about 40 hours before ovulation, transforming the primary oocyte into a secondary oocyte, which then begins the second meiotic division. The released egg cell temporarily halts in the middle of this second division.

If the egg meets sperm after ovulation, fertilization triggers the completion of the second meiotic division, forming a fertilized egg. It is at this point that the egg cell fully completes meiosis and becomes what is often referred to as an “ovum.” However, by this time, fertilization has already occurred, so no one ever actually sees a true ovum; what we refer to as the “egg” is already in the process of becoming a fertilized zygote.

The other primary oocytes that were awakened but not used will degenerate and disappear—a process known to doctors as “atresia.”

Each resilient and energy-packed egg cell contains a haploid set of chromosomes, meaning the chromosome count is halved. This allows the mother to provide half of the genetic material needed to create a baby.

A woman has about 400 primary oocytes in her lifetime that have the opportunity to develop and reach the ovulation stage—truly a case of “one in a million.”

After the long process of meiosis, each primary oocyte produces one egg cell and three polar bodies, which eventually degrade and disappear.

Egg cells are sensitive to cold, which is why the ovaries are located in the warmest part of the pelvic cavity, where they can be kept comfortably warm.