Question

In vitro fertilisation is a technique that involves transfer of which one of the following into the fallopian tube?

• A. Embryo only, upto 8 cell stage
• B. Either zygote or early embryo upto 8 cell stage
• C. Embryo of 32 cell stage
• D. Zygote only

Answer 1

The correct option is B Either zygote or early embryo upto 8 cell stage

In the in vitro fertilisation technique, fertilisation takes place in a simulated laboratory environment, outside the body of the female parent. The subsequent steps are decided based on the developmental stage of the zygote. If the undivided zygote has to be transferred into the female reproductive tract, then it is transferred into the fallopian tube. The zygote continues cleavage division on its way to the uterus.
If the zygote is allowed to undergo cleavage in vitro (to check the success of fertilisation and the viability of the resulting zygote), then the early embryo upto 8 cell stage is transferred into the fallopian tube. Embryo at 16 cell stage or more is directly transferred into the uterus. It is because implantation mostly occurs at the 16 celled stage. The proper site of implantation is the uterus. So, the 16 celled embryo must be present in the uterus for proper implantation. If it is present at any other part other than the uterus, then it might lead to ectopic pregnancy (implantation of embryo at any other part of the female reproductive tract other than the uterus).