Chances of Twins with IVF: Everything You Need to Know

What Are Twins in IVF and How Do They Occur?

Similar to natural conception, IVF pregnancies can result in twins: either two eggs are released and fertilised separately (fraternal twins) or the fertilised egg splits into two embryos (identical twins).

Here’s how it works:

• Fraternal twins (dizygotic twins) : Two eggs are fertilised by two sperm and give rise to two genetically distinct infants.
• Identical (monozygotic) twins : The embryos of a single fertilised egg split into two when they are still developing. These twins have the same genetic content.

Twins during IVF may occur when:

• Several embryos are implanted in the uterus.
• Only one embryo splits after transfer - an infrequent, but possible, occurrence.

Can a Single Embryo Split into Twins?

It might seem surprising, but even a single embryo transfer during In Vitro Fertilisation can sometimes produce identical (monozygotic) twins. This occurs when a fertilised egg naturally divides after being placed in the uterus, resulting in two separate embryos.

Here’s how it happens:

• One fertilised egg (zygote) separates into two different groups of cells at the early stage of its development.
• Later, each of them has the same genetic material since they come from the same original one, i.e., identical twins.
• The timing of this split decides how the twins share their placenta and amniotic sac:

Possible scenarios include:

• Early split : Two placentas and two amniotic sacs (dichorionic-diamniotic twins) in an early division.
• Later split : One placenta, two amniotic sacs (monochorionic-diamniotic twins) when the division occurs later.
• Very late split : One placenta and one amniotic sac (monochorionic-monoamniotic twins), the most uncommon and riskiest due to the sharing of both space and circulation, resulting in very late division.

The occurrence of identical twins cannot be predicted, nor can the timing of the twinning be controlled in an IVF programme.

Chances of Twins After Embryo Transfer

The biological process of division usually occurs within the first week after embryo transfer, during implantation. However, the likelihood of this event can be affected by several factors:

• Embryo quality and stage : The better the quality of the blastocysts, the more viable they are, and thus the probability of spontaneous division may be a bit higher.
• Laboratory techniques : Procedures like ICSI (intracytoplasmic sperm injection) and assisted hatching have only been slightly associated with the occurrence of monozygotic twins.
• Frozen versus fresh embryos : There are a few scenarios that imply a situation in which frozen embryos may have a slight risk of dividing.
• Maternal age : Younger women, particularly those under 35, tend to have a higher implantation rate, which also increases the likelihood of twins.

Twin pregnancies after IVF are certainly joyful, but on the other hand, they are more demanding and therefore need to be closely monitored.

Factors That Increase the Chance of Twins in IVF

Certain biological and procedural factors can raise the probability of twin pregnancies in IVF cycles:

• Maternal Age : Women of younger age (below 35) usually generate eggs and embryos of better quality; thus, the probability of implantation and in rare cases, identical twinning, is increased.
• Embryo Quality : High-grade blastocysts have a greater capacity for development and might divide on their own, but in an unpredictable way.
• Hormonal Environment : The use of support hormones for the uterine lining can increase the chances of multiple implantations.
• Frozen vs Fresh Embryos : There is some indication that the rate of monozygotic twinning in frozen embryo transfer is slightly higher than that in fresh transfer.
• Blastocyst Transfer : Transferring embryos at the five-day blastocyst stage results in a higher chance of implantation, and this may explain the very few cases of splitting attributed to this stage.
• Number of Embryos Transferred : Transferring more than one embryo increases the chances of twins, triplets, or quadruplets accordingly. This is why clinics are increasingly advocating for single embryo transfer (SET).

Risks of Twin Pregnancy in IVF

Twin pregnancies, though often a source of happiness, also involve a certain level of medical risks that require extra care and attention.

Risks for the mother:

• Gestational diabetes : The risk is twofold, stemming from hormonal fluctuations and heightened nutritional needs.
• Pre-eclampsia : The risk increases due to the larger volume of blood and the more intricate placenta.
• Preterm labour : The uterus cannot hold the twins for the full term, and thus the delivery is earlier.

Risks for babies:

• Low birth weight : The reason is that newborns from multiple births are usually smaller and have a lower birth weight at the time of birth.
• Respiratory distress or NICU admission : A premature baby may need respiratory support.
• Twin-to-twin transfusion (for identical twins sharing a placenta) : Requires very close and specialised monitoring.

Modern medical supervision, along with planned prenatal care, though these risks remain, has made it possible for most twin pregnancies to end with positive outcomes.

Reducing the Risk of Twins in IVF

Fertility doctors usually apply several evidence-based measures to ensure a safe pregnancy and limit the occurrence of multiple births:

• Single Embryo Transfer (SET) :
  By transferring only one top-quality embryo, the chances of a twin pregnancy are significantly reduced, and the success rates remain practically the same.
• Proper Embryo Selection :
  The use of intensive embryo grading and genetic screening methods allows for the selection of the embryo most suitable for transfer.
• Personalised IVF Planning :
  The treatment adjusted to a woman’s age, state of health, and prior response to IVF is a way of cutting down on unnecessary embryo transfers.
• Monitoring Hormone Levels :
  Hormonal treatment is administered in a balanced manner, providing a favourable implantation phase without the risk of overstimulation.

Conclusion

While the idea of twin pregnancies via IVF is touching, it isn't entirely controlled by medical professionals. Occasionally, a single embryo may split into two, creating identical twins- though this is uncommon. Factors such as maternal age, embryo quality, and transfer techniques can affect these probabilities. Nevertheless, modern fertility treatments aim for a safe and healthy pregnancy, typically involving one baby at a time. Indira IVF provides personalised support and detailed fertility planning, empowering couples or individuals with expert guidance and informed choices throughout every stage of treatment.