This lesson introduces the concept of fertilization, and then uses that background information to explain the details behind in vitro fertilization (or IVF). A summary and brief quiz are included at the lesson’s conclusion.
Overview of Fertilization
Most people are familiar with the concept of fertilization: the idea that sperm cells join egg cells to produce zygotes, otherwise known as fertilized eggs. However, what people might be less familiar with is how normal fertilization differs from in vitro fertilization (IVF). Each of these processes can produce a healthy individual, but they differ in form and complexity. For example, fertilization normally occurs when a sperm fuses with the mother’s egg inside the uterus or fallopian tube.
This is how most fertilized eggs are produced and chances are, it’s how you were created; however, when people have difficulty conceiving a child naturally, they may choose to explore another method of fertilization such as IVF.
In Vitro Fertilization
The primary difference between IVF and natural fertilization is that IVF involves removing sperm and eggs from the parents’ bodies for fertilization outside the body. The sperm is used to fertilize an egg under controlled conditions within a laboratory setting.
If successful, the fertilized egg (zygote) further develops into an embryo, and then is implanted back into the mother’s uterus to undergo an otherwise normal development process. While this method of fertilization seems simple, it is actually very complicated.The initial step of in vitro fertilization involves the woman taking hormone supplements that stimulate her ovaries to release multiple eggs, rather than the typical one egg per month. If the stimulation is successful, these eggs are then carefully harvested. The timing of this harvest is critical; too early or too late a harvest, and the eggs may not develop properly.To harvest eggs, doctors use a hollow needle to collect the eggs directly from the ovarian follicles.
During the procedure, many women will receive pain medication, be mildly sedated, or undergo full anesthesia. Upon retrieval, the eggs are mixed with the father’s sperm and fertilization is allowed to occur. Then, under clinical supervision, the fertilized eggs are allowed to develop for several days.
After the eggs have grown and are ready, doctors use a flexible tube to implant the developing embryo back into the woman’s uterus.
This procedure is simpler than egg retrieval and typically involves no sedative or anesthesia. However, this is where things become considerably less controlled because there is no guarantee that deposited embryos will survive. In fact, the majority of embryos are unlikely to remain viable following their introduction back into the uterus. The success rate varies widely depending on the mother’s age, health, and other factors; one study estimated that approximately 25% of implanted embryos result in a live birth. For this reason, most doctors recommend implanting multiple embryos, thus increasing the likelihood of success for one of them.
Yet, in some cases, multiple embryos do survive and develop into healthy children. Therefore, IVF could help couples have one child or multiple children, depending on how many embryos are implanted, and the success rate of the embryo implantation.
Many couples across the world have children under seemingly natural conditions. Fertilization occurs when sperm and egg meet inside the mother’s body and a zygote is formed.
However, this zygote (or fertilized egg) is not always created easily. In fact, some couples have difficulty conceiving a child and must therefore explore other options. In vitro fertilization is once such option. In IVF the donor sperm cells and egg cells are joined outside the mother’s body within a controlled laboratory setting. If successful, the newly formed zygotes are allowed to develop for several days before being implanted back into the uterus. Once implanted, one or more of the cells (now referred to as embryos) will continue to develop naturally and may eventually result in one or more children, depending on the survival rate of reintroduced embryos.