Royal Prince Alfred Hospital
Fertility Unit
Royal Prince Alfred Hospital

Fertilisation & Implantation


When the egg and sperm meet in the fallopian tube, the sperm start to burrow through and enter the egg. At the moment the first sperm successfully penetrates the egg, a reaction is triggered that makes the egg resistant to all other sperm. This single sperm absorbs into the egg, where the genetic material contained in its head fuses with that of the egg. This is fertilisation.

The egg maintains its ability to be fertilised for about 12 hours after ovulation. Sperm can remain active in the cervical mucus for 48-72 hours or more around the time leading up to ovulation.


The fertilised egg, now known as an embryo, develops in the fallopian tube for the first three days, then travels down into the uterus. By the fifth day it will become a blastocyst, a hollow ball of cells surrounding a cyst-like cavity. Once the blastocyst breaks free from its shell, or hatches, it is ready to attach to the lining of the uterus. If implantation occurs, the ruptured follicle (corpus luteum) increases the production of progesterone to support the pregnancy. If pregnancy does not occur, hormone production falls and the lining of the uterus is shed, resulting in a period.

A home pregnancy test will detect pregnancy hormone by Day 28 of a menstrual cycle.