Natural Conception Vs IVF

Many people talk quite freely about IVF, about how it can help infertile couples to conceive a child.  However, how many people actually know all the details, whether it is about a naturally conceived child, or through the aid of IVF, how much do people know?

Natural conception!

This is how most of us came to be, through the joining of two parental gametes, the oocyte (egg) and the sperm.  After being released as a result of sexual intercourse, sperm have a tough journey through the female genital tract, and many do not survive before reaching the uterine tubes- the location of the egg.  The sperm are aided in this passage by the fructose rich fluid they are in that provides the much needed energy.  Once the successful sperm have reached the egg they must undergo capacitation- this prepares the sperm for entry into the egg by removing glycoproteins on the acrosome as well as changing the membrane potential and charge.fertilisation02

The successful sperm then penetrates the layers of the egg, which in turn prevents other sperm from doing the same.  The part of a sperm cell called the acrosome releases enzymes such as hyaluronidase, and receptors bind to ZP3 molecules on the egg which allows the sperm to break through the layers of the egg, the corona radiata and zona pellucida [1] . This allows for the fusion of the two gametes, with only the head of the sperm entering the egg cytoplasm, causing reactions that prevent other sperm from doing the same [2].  It really is a race to the finish line! The fertilised egg then becomes known as a zygote [3].  The two nuclei of the sex cells fuse and the chromosomes pair up, allowing cell division (mitosis) to occur as it moves down the fallopian tubes towards the uterus, where the growing ball of cells continues to divide and differentiate for 9 months until a baby is born!


IVF is when the fertilisation of an egg by a sperm happens outside of the human body.  The egg and sperm are taken from the two future parents and the two gametes (the egg and the sperm) are placed together in a culture medium which allows fertilisation to occur.  The fertilised egg will then start to multiply, and upon reaching the 6-8 cell stage, the embryo is placed directly into the women’s uterus in the hope it will continue to grow as a naturally fertilised egg would.  This is achieved through implantation of the embryo into the uterus wall, making a firm connection needed for the embryo to get nutrients from the mother.  Either one or two fertilised eggs can be inserted back into the woman, however, multiple embryos run the risk of multiple pregnancy.


So whether a baby is born through natural conception, a process that has been occurring for millions or years, or through the relatively new method of IVF, once implantation occurs, the fertilised egg, or the embryo continues to grow.  If everything goes well then the embryo develops into a foetus, developing more human characteristics every day, until after 9 months of being lovingly carried around by the mother, a baby is born into the world! An amazing end product of months of endless chemical reactions and the growth of cells.

References/extra reading

[1] Finlayson and Sanders (2007) Endocrine and Reproductive Systems. Mosby Elsevier. Page 177

[2] Patrat, Serres and Jouannet (2000), The acrosome reaction in human spermatozoa, Biology of the Cell 92: 255-266



IVF Video Podcast. Patrick Steptoe FRCS, FRCOG – “Test Tube Baby – The First Birth”

Amazing video of the birth of Louise Brown in 1978, the First Test Tube baby!
Born at 5lb 12oz with a “good healthy cry.” The first of many IVF babies to be born.

louise brown

Louise Brown, at birth in 1978, and much more recently!

My DNA your egg

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