In general, transfer of one embryo at a time is best and will result in 1.5% of pregnancies being twin pregnancies (1). In health women above age 35 or with low quality embryos transfer of more than one embryo can sometimes be a reasonable cost effective approach. When more than one embryo is transferred at at time it is best to aim to have a twin rate (percentage of ongoing pregnancies resulting from an embryo transfer that are twins) of 20% or less and a triplet rate of less than 1%. The tables below can be used to predict the rate of twins and triplets after transfer of more than one embryo (2).

Awadalla MS, Bendikson KA, Ho JR, McGinnis LK, Ahmady A. A validated model for predicting live birth after embryo transfer. Scientific reports. 2021 May 24;11(1):10800.

https://pubmed.ncbi.nlm.nih.gov/34031492/