In this study, the risk of birth defects was increased with IVF but was no longer significant after adjustment for maternal factors. The risk of birth defects associated with intracytoplasmic sperm injection remained higher after multivariate adjustment. Residual confounding cannot be ruled out. Consistent evidence from individual studies, including registry-based cohort studies 1 , 2 and meta-analyses, has linked assisted conception involving in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) with an increased risk of birth defects. 3 – 8 The associations between the use of these techniques and birth defects have appeared to be stronger for singleton births than for multiple births. 9 , 10 It is unclear whether the excess of birth defects after IVF or ICSI may be attributable to patient characteristics related to infertility, 8 rather than to the treatment, and whether the risk is similar across assisted reproductive technologies and related therapies. 3 , 11 , . . .