The ovum (or egg) is a female’s gamete, or sexual reproductive cell and contains the genetic material necessary to create offspring. Ovum are created and stored in a female’s ovaries, which are connected on either side of the uterus by the fallopian tubes. At birth, a female has approximately one million undeveloped ova in each of her ovaries; many of these deteriorate and are reabsorbed by the body. Unlike male sperm, however, females are unable to generate new ova. By the time a female reaches puberty (around age 12), she has only around 200,000 ova in each ovary.1 The number of ova in a female’s ovaries continues to decrease at a constantly increasing rate as she grows older and undergoes menstruation.
An Ovum’s Journey
Typically, the left and right ovaries take turns releasing one ovum during each menstrual cycle. During this stage, each oocyte (or undeveloped ova) is surrounded by supporting cells, which help the ovum develop; this casing is known as the “follicle”. After an ovum is released during ovulation, cilia-lined fimbria (finger-like structures) catch the egg and channel it to the connecting oviduct (also called the fallopian tube). While in the oviduct, the egg travels at a rate of about one inch every 24 hours. At this point in the cycle the egg has the potential to be fertilized by the sperm (male reproductive cell). An egg can be fertilized in the oviduct 24 to 48 hours after ejaculation. If a sperm and egg meet, the sperm buries its nucleus into the egg in a process known as fertilization. The fertilized egg then develops into a zygote and implants into the endometrium of the uterus where it continues to develop. If the egg is not fertilized by a sperm, it passes through the female’s cervix and out through her vagina with the shedding endometrium during menstruation.1
Blighted ova are eggs that have undergone irregular cell division and contain problematic chromosomes (genetic material). During a normal pregnancy, an ovum implants into the endometrium in the uterine wall, the gestational sac grows around the ovum, and the ovum (now gamete) develops into an embryo. In blighted ova, the gestational sac grows, but the embryo does not develop. This is termed an “anembryonic pregnancy”. Blighted ova cause one out of every two miscarriages during the first trimester. A female with blighted ova may experience abdominal cramps, vaginal bleeding or spotting, or a period that is heavier than usual.2 She should contact a doctor if she experiences any of these symptoms during her pregnancy.
Ova and Infertility
Ova quantity and quality decrease as a female grows older. The rate of deterioration increases when the woman reaches 35 years of age.3 Egg loss or “loss of ovarian reserve” is often blamed for a female’s infertility (inability to reproduce). However, there are many other issues that complicate a female’s ability to conceive a child. Damage to the oviducts, hormonal irregularities, cervical conditions, and uterine problems also affect a female’s fertility.4
1. Baldwin, Janice, Baldwin, John, and LeVay, Simone. Discovering Human Sexuality. Sunderland: Sinauer Associates, Inc., 2012. Print.
2. Thrasher, Melinda M. "Blighted Ovum: Causes, Symptoms, and More." WebMD. WebMD, 24 Mar. 2013. Web. 31 Oct. 2014.
3. ASRM, Staff A. "Resources." ASRM Patient Fact Sheet: Reproductive Aging in Women. American Society for Reproductive Medicine, 2012. Web. 31 Oct. 2014.
4. Todd, Nivin A. "Female Infertility: Causes, Tests, Signs, Treatments." WebMD. WebMD, 21 June 2012. Web. 31 Oct. 2014.
Last Updated 31 October 2014.