Ovulation is a biological process in the female reproductive system, involving the release of a mature egg. This event is a central component of the menstrual cycle, marking the period when pregnancy can occur. Once released, the egg travels into the fallopian tube, where it may be fertilized, leading to conception.
The Standard Ovulation Process
The typical ovulatory cycle involves a complex interplay of hormones that prepare the body for potential pregnancy. Each month, the hypothalamus releases gonadotropin-releasing hormone (GnRH), which prompts the pituitary gland to produce follicle-stimulating hormone (FSH) and luteinizing hormone (LH). FSH stimulates several follicles, small fluid-filled sacs in the ovaries, to begin maturing. As these follicles grow, one usually becomes dominant, continuing to develop while the others recede.
Around the middle of the menstrual cycle, often about 14 days before menstruation, an LH surge occurs. This surge triggers the dominant follicle to rupture, releasing its mature egg from the ovary. The egg then travels through the fallopian tube. While it is commonly believed that the two ovaries alternate releasing an egg each month, research indicates this pattern is not strictly regular; ovulation can occur from either ovary, and sometimes from the same ovary for several consecutive cycles.
Ovulation from Both Ovaries
While a single egg release is the norm, it is biologically possible for both ovaries to ovulate within the same menstrual cycle, a phenomenon known as hyperovulation or multiple ovulation. This can happen in two ways: one ovary releases an egg, and then the other ovary releases an egg shortly after within the same cycle, or both ovaries release an egg simultaneously. When two eggs are released and both are fertilized by separate sperm, this results in fraternal (non-identical) twins. Multiple eggs are released during a single ovulatory event, not at different times across days within a cycle.
Several factors can increase the likelihood of hyperovulation. Genetic predisposition plays a role, as a family history of fraternal twins can suggest an inherited tendency for multiple egg release. Advancing age can also contribute, as diminishing ovarian reserve may lead to higher FSH levels, potentially stimulating more than one follicle to mature. Fertility treatments, such as those involving medications like clomiphene citrate or in vitro fertilization (IVF), are designed to stimulate the ovaries and frequently result in the release of multiple eggs.
Ovulation with a Single Functioning Ovary
For individuals with only one functioning ovary, perhaps due to surgical removal or a congenital condition, the body adapts to maintain reproductive function. The remaining single ovary is capable of taking over the ovulatory process. This single ovary can release an egg every menstrual cycle, compensating for the absence of the other.
Having only one ovary does not necessarily reduce fertility by half. The remaining ovary often undergoes a process known as compensatory hypertrophy, where it increases in size and activity. While other factors like age or underlying medical conditions affecting the remaining ovary can influence fertility, the single ovary is generally able to sustain regular ovulation.