Once an egg has been fertilised, it is now known as a zygote. The zygote starts an epic journey taking three or four days, back down the fallopian tube and into the uterus. During this journey, the zygote already gets started growing, dividing into 16 identical cells and at this point it’s called the morula.
By the time the morula enters the uterus, it’s grown into a ball packed with cells and has earned itself yet another name change to become the blastocyst. Over the next two days, the blastocyst will attempt to burrow into the lining of the uterus that your body has carefully prepared – this will be the nest for the first stage of your baby’s growth.
Early Pregnancy Factor (EPF), an immuno-suppressant protein, is first manufactured by your body now. Without EPF, your body might mistake the developing baby for a foreign body (like bacteria or a virus) and attack it. With EPF, your baby can continue to develop without risk.
When the cell ball comes to rest on the surface of your uterus, the process of implantation begins. During implantation, the outer cells that have made contact literally fuse with the cells on the surface of your uterus. Implantation protects the blastocyst and provides it with oxygen and nutrients from your bloodstream.
The actual size of the implanted cell ball is 0.1mm, about the size of a pinhead or the full stop at the end of this sentence.
Early symptoms of pregnancy
You can read about the most common early symptoms of pregnancy in our handy guide.