Briefly explain $IVF$ and $ET$. What are the conditions in which these methods are advised?

(N/A) $IVF$ (In vitro fertilisation) is a process where fertilisation occurs outside the body in conditions similar to those in the body, followed by $ET$ (Embryo Transfer).
In this method, commonly known as the $test-tube-baby$ programme, ova from the wife/donor and sperms from the husband/donor are collected and induced to form a zygote in the laboratory.
The zygote or early embryos (up to $8$ blastomeres) are transferred into the fallopian tube ($ZIFT$ - Zygote Intra Fallopian Transfer), while embryos with more than $8$ blastomeres are transferred into the uterus ($IUT$ - Intra Uterine Transfer) for further development.
These methods are advised for couples suffering from infertility, such as cases where the female has blocked fallopian tubes, low sperm count in the male, or unexplained infertility where natural conception is not possible.