IVF and Multiple Births


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Multiple births is a name for a phenomenon that most of us have become familiar with at some point or another, the birth of twins, triplets, and in some cases up to 6 or 7 babies at a time. Multiple births are one of the major side effects of IVF, and will be discussed in more detail in this article which aims to give you all you need to know about the ins and outs of multiple births and its relevance to IVF.

What is a multiple birth?

A multiple birth is any occasion where more than a single foetus (unborn child) is born at the end of a pregnancy. The most common number of births that emerge out of these scenarios is 2, and while still relatively infrequent, 3 births do happen as well. These are referred to as twins and triplets respectively, and while these are the most frequently occurring multiple births, it is possible to give birth to up to as many as 7 or 8 babies through a single pregnancy.

How does a multiple birth happen?

Children are conceived when the female egg is fertilised by male sperm, after this event the two cells are fused and form what is called a zygote, which then goes on to divide to form an embryo. Normally a single egg is fertilised and becomes a single zygote which grows into a single embryo, then foetus, then baby. What happens during a multiple birth is that multiple embryos are formed by one of two different ways.

A single zygote can split to form different embryos that grow into what are called monozygotic siblings. Monozygotic is a fancier word for identical siblings, most commonly known as identical twins, because they share the same genetic material and so look identical. Alternatively, more than one egg could be fertilised and develop from there to form fraternal or dizygotic multiple siblings. In some rare cases multiple births can be polyzygotic, which means that there is a combination of fraternal and identical siblings.

IVF and multiple births

There is a higher likelihood of multiple births occurring after fertility treatments, most notably IVF. This is because during a cycle of IVF multiple embryos are implanted into the womb to give the best chances for a successful cycle in which an embryo is carried through to full term. A natural risk therefore is that one or more of these embryos implants successfully, which may be undesirable for some couples and carries with it some risks and hazards.

Risks and side effects of multiple pregnancies after IVF

The HFEA describes multiple pregnancies as the biggest risk involved in fertility treatments. These events are far more likely after IVF, which carries a 25% likelihood compared to a one in 80 chance after natural conception. Multiple pregnancies have a much higher risk of disability in the children after birth, early death, and stillbirth. Babies born from multiple pregnancies tend to be premature and there is also a risk of an incomplete separation resulting in what are known as Siamese or conjoined twins. This is a phenomenon where an embryo doesn’t complete its split into two separate embryos, and the resulting children are fused.

With so many health risks attached to multiple pregnancies, it is no surprise that the HFEA is determined to reduce the risk of multiple pregnancies and births. Techniques like IMSI, where the best sperm are selected to yield a viable embryo for implantation, and metabolomics, where the best and most viable embryos are selected, aim to reduce the number of embryos introduced for implantation and hence minimise the risk of multiple pregnancies. New measures are evolving and being refined, and the hope is that in years to come the incidence of multiple births and pregnancies will be dramatically reduced.


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