IVF allows women to delay birth and pursue careers, but IVF massively increases the risk of twin birth. There is limited evidence of how having twins influences women's post-birth careers. We investigate this, leveraging a single embryo transfer (SET) mandate implemented in Sweden in 2003, following which the share of twin births showed a precipitous drop of 70%. Linking birth registers to hospitalization and earnings registers, we identify substantial improvements in maternal and child health and women's earnings following IVF birth, along-side an increase in subsequent fertility. We provide the first comprehensive evaluation of SET, relevant given the secular rise in IVF births and growing concerns over twin birth risk. We contribute new estimates of the child penalty imposed by twin as opposed to singleton birth, relevant to the secular rise in the global twin birth rate.