Ovulation is a fundamental event in the female reproductive cycle, representing a window for conception. This process involves the release of a mature egg from an ovary, making it available for fertilization by sperm. Its timing is precisely regulated by hormonal signals, preparing the body for a potential pregnancy. Successful ovulation is a prerequisite for natural conception.
The Typical Ovulation Process
Ovulation typically involves the development and release of a single, dominant egg. Each menstrual cycle begins with the follicular phase, where several follicles, which are small fluid-filled sacs containing immature eggs, start to grow within the ovaries. This growth is stimulated by follicle-stimulating hormone (FSH) from the pituitary gland.
As follicles develop, they produce estrogen. Eventually, one follicle surpasses the others in growth and becomes the dominant follicle. The dominant follicle continues to produce increasing amounts of estrogen, which then signals the pituitary gland to reduce FSH production, causing the other developing follicles to stop growing and degenerate.
The high estrogen levels from the dominant follicle then trigger a surge in luteinizing hormone (LH) from the pituitary gland. This LH surge causes the dominant follicle to rupture, releasing its mature egg into the fallopian tube. The released egg remains viable for fertilization for approximately 12 to 24 hours.
When Multiple Eggs Are Released
While the release of a single egg is typical, there are instances where more than one egg is released during a single ovulation cycle, a phenomenon known as hyperovulation. This can lead to the conception of fraternal (dizygotic) twins, which occur when two separate eggs are fertilized by two different sperm cells. Unlike identical (monozygotic) twins, which result from a single fertilized egg splitting, fraternal twins are genetically distinct.
Several factors influence hyperovulation. Genetic predisposition is one, as a tendency to release multiple eggs can run in families, particularly on the maternal side. Maternal age is another contributing factor; women over 35 have an increased chance of releasing more than one egg. This is partly due to naturally rising FSH levels as a woman approaches menopause, which can stimulate multiple follicles.
Fertility treatments also increase the probability of multiple egg release. Medications designed to stimulate ovulation can cause the ovaries to produce and release several eggs simultaneously. Similarly, in vitro fertilization (IVF) procedures often involve transferring multiple embryos into the uterus to enhance pregnancy rates, which can result in twin or higher-order multiple pregnancies if more than one embryo successfully implants.