In order to assess the available evidence on the adverse health effects of in vitro fertilization (IVF), this meta-analysis investigates whether IVF increases the propensity of low birth weight (<2,500 grams) and preterm delivery (<37 weeks of gestation) in singletons. Ten studies containing the birth weight and/or gestational age at birth of a total of 48,484 IVF-conceived and 3,654,576 naturally conceived singletons were included. The results suggest that IVF singletons are more likely to be of low birth weight (OR = 1.60, CI95% 1.22 - 2.24) and to be delivered preterm (OR = 1.76, CI95% 1.18 - 2.50). IVF singletons are also more likely to be of low birth weight than naturally conceived singletons, even when born at term (OR = 2.00, CI95% 1.72 - 2.34). These results not only lead to the consensus that singletons conceived through IVF are more likely to be delivered preterm than naturally conceived singletons, but also implicate that IVF singletons are of lower birth weight, independent of gestational age. Further research should elucidate whether the observed effects can be attributed to the underlying infertility, or the procedural and environmental differences between in vitro and natural conception.