There is always a chance of twins with IVF, but most IVF pregnancies are a single baby. The risk of twins is affected by how many embryos are transferred into your uterus, your age, the stage of the embryos (day 5 or 6 blastocyst-stage embryos are more likely to implant than day 2 or 3 cleavage-stage embryos), and the quality of the embryos. If you are under 35 with high quality embryos, there is about a 40% chance of twins if two embryos are transferred, and less than a 5% chance of twins with one embryo transferred – a single embryo can split into identical twins. Blastocysts are more likely to split.
Identical twins from IVF is a rare event. Most twins from IVF are non-identical, from two different embryos. Not all pregnancies that start as twins end as twins – some twin pregnancies result in miscarriage of one twin and survival of the other one so that you end up with a single baby.
The pregnancy rate with IVF may be up to 10-20% higher with two or more embryos transferred compared to a single embryo. The ideal candidate for a single embryo transfer is a woman under 35 using her own eggs (or any age using an egg donor under 35) with good quality embryos, and preferably with extra embryos available to freeze. It’s also preferable if it’s your first IVF cycle, or you’ve been successful with IVF before.
Talk to your MD about your concerns regarding twins and together you can decide the right number of embryos to transfer. They can give you specific guidance as they know your individual situation.