Beyonce and Amal Clooney? Seems like twins are more common these days….
Twin births have always been part of nature but with rising twin rates in modern times IVF has a lot to answer for.
Twin births have always been part of nature but with rising twin rates in modern times IVF has a lot to answer for.
Identical twins: Nature vs In Vitro Fertilization (IVF)
Identical or “monozygotic” twins, (where a single egg and sperm combine to form an early embryo, which goes on to “split”, forming two babies) occur in about 1 in 400 birth with natural conception. The rate of this happening is pretty consistent across all populations and races. This suggests an embryo splitting after natural conception is a random event and isn’t influenced by your genes.
In IVF however, identical twin rates quoted in the medical literature are as high as 1-3%. It is thought that handing of embryos in the lab is to blame for the higher risk of identical twins conceived throught IVF.
Fraternal Twins: Nature vs Assisted Reproduction
Fraternal, dizygotic, “non-identical” or “two egg” twins (where two eggs are simultaneously released and fertilized by two separate sperm cells to form two genetically distinct embryos) can have varying incidence in different racial groups. Sometimes a tendency to this trait can run in families.
For example in Caucasian populations, dizygotic (two egg) twins occur in 8 in 1000 births. In African populations, twins are twice as common (16 in 1000 births), whereas in Asian populations it’s only 4 in 1000 births affected.
In Australia, overall, about 1 in 80 births are twins so how does this compute?
The simple answer is assisted reproductive treatments, and not just IVF.
Techniques like ovulation induction and intrauterine insemination are to blame for more twins than are naturally conceived. Using these techniques, specialists use medications (like clomiphene, letrozole, tamoxifen or follicle stimulating hormone) that induce ovulation of multiple eggs in the same cycle.
Also to blame is IVF and the process of double embryo transfer, or simply put, putting back two embryos at the same time.
The idea of twins is pretty gorgeous and most couples wrestling with infertility at some point idealize the concept of an “instant family”, “job done” or “two for the price of one”. But IVF experts now agree on the most part that single embryo transfer should in fact be gold standard.
Why shouldn’t aiming for twins be the IVF practice norm?
Twin pregnancies are by definition higher risk affairs. Mothers face increased risks of high blood pressure and pre-eclampsia, gestational diabetes and operative deliveries (c-sections) while babies face higher risk of growth restriction (due to an overtaxed placenta and limited physical room) and premature delivery. It is preterm birth that carries a lot of danger for twins, and the earlier they are born, the more likely they are to suffer developmental injuries. Issues can range from problems with vision and hearing to respiratory and cognitive developmental problems, cerebral palsy and learning disabilities.
Humans are definitely best designed to have one baby at a time.
So why would an IVF doctor put back two embryos?
Before we got really good at growing and freezing embryos in the IVF lab, doctors considered the best thing we could do by our patients was to perform double embryo transfers (to improve the chance of conceiving with IVF in a given month). We used to accept as a trade off, an increased twin rate affecting up to 50% of IVF pregnancies. In more modern times, with thanks to vitrification freezing technology, in the best IVF units like ours, pregnancies are now equally as likely to result from frozen embryo transfers. This fact gives me confidence that by freezing your embryos we are not compromising your ultimate chance of having a baby.
So did Beyonce and Amal have IVF? Maybe. But isn’t the real question “so what”? In Australia today there is statistically at least one IVF baby in every classroom and, in my opinion, overcoming infertility is a tremendous thing.
Written by Dr Raelia Lew
RANZCOG Board Certified CREI Fertility specialist, Gynaecologist and the Director of Women’s Health Melbourne.
Co-host of the Knocked Up Podcast, Co-founder of Lovers intimate wellness solutions. Raelia has a PhD in Preconception Health Promotion and Genetic Screening. Raelia is a leading Australian expert in IVF and egg freezing, pioneering a bespoke model of care.