In Vivo vs. In Vitro Fertilization: Key Differences

Fertilization is a process in which fusion of sperm with an ovum to form an embryo takes place during sexual reproduction. Fertilization has been classified into two: External fertilization and internal fertilization.

Let’s discuss below the difference between external and internal fertilization.

Internal Fertilization (In Vivo)

In this type of fertilization, the fusion of sperm with egg occurs within the body of a female. Here, the male discharges the sperm into the female genital tract and the development of the embryo happens inside her uterus.

Internal Fertilization is a natural process and it only requires a single egg from a single egg follicle to produce an embryo. So it means very few gametes are required for an internal fertilization.

Since the fertilized egg stays isolated within the tough protective layers of the uterus in the female body, the survival rate of the embryo is higher in internal fertilization.

Most of the women who conceived naturally through internal fertilization have single offspring; except in few such cases where they conceive twins, triplets or more. Chances of babies born with abnormalities though internal fertilization are less in comparison to external fertilization.

External Fertilization (In Vitro)

External fertilization is a process in which the fusion of the sperm and egg happens in an IVF laboratory. Here, the extraction of eggs and sperms is required for this type of fertilization.

Fertility medications are given to control the timing of the egg ripening. Both the ovaries of the woman are stimulated to grow and mature multiple egg follicles. So a large number of gametes are required in external fertilization.

After the egg development has been monitored by an ultrasound, it is retrieved through the transvaginal aspiration technique. A required amount of sperm is also collected from the man’s semen sample. A highly trained embryologist will then place a single sperm into each egg in an IVF laboratory using highly sophisticated equipment.

The fused eggs and sperm needs to be kept in incubators to provide all the correct conditions for a successful fertilization. Five days post-retrieval, the embryos are transferred to the uterus.

As the survival rates of these embryos inside the womb are less when compared to internal fertilization, one or more high-quality embryos are transferred into the uterus. Since more than one embryo is transferred, the risk of multiple pregnancies is higher in external fertilization.