Couples undergoing in vitro fertilization for infertility often face an excruciating choice: Should they have two or possibly three embryos implanted and run the risk of having twins or triplets, or should they have a single embryo implanted with the greater likelihood that no pregnancy will be achieved at all?

Previously, doctors used age as a way to calculate the prospect of multiple births, but a new formula that considers multiple factors beyond age — developed using data from the fertility center Boston IVF — is far more reliable and could ultimately reduce multiple births resulting from IVF procedures, according to a study published Monday in the journal Fertility and Sterility.