Fertilisation must occur soon after the release of the ovum to the uterus. The egg usually gets fertilised in the outer third of a fallopian tube, the ampulla portion. The functional life span of spermatozoa is about 48 hours (it may be as long as 72 hours or longer) while that of the ovum is about 48 hrs. Therefore, sexual coitus during this time may result in fertilisation (pregnancy).

The sperm (figure 3.1.a) should be able to swim up the fallopian tube and fuse with the ovum to effect fertilisation. In this regard, usually, one active spermatozoon is sufficient to penetrate the membrane of the egg and fuses with its nucleus (See figure 3.1.b, below).

Fig 3.1a. Structure of spermatozoa
Fig 3.1b. How fertilisation takes place

The zygote or blastocyst is called the embryo. The embryonic period extends from the day of fertilisation up to the seventh week of gestation and is the stage (period) when the primary structures of the conceptus are formed.

Conceptus is all the tissue products of conception which transform into foetus and placenta over the next few weeks if the fertilised egg implants.

Last modified: Thursday, 10 November 2016, 5:59 PM