Background: Results regarding the association between mercury exposure and anthropometry at birth, gestational length and placental weight are inconsistent, as is the role of seafood intake in these asso- ciations. Objective: We assessed whether prenatal mercury exposure is associated with anthropometry at birth, placental weight and gestational length in a population with a relatively high exposure to mercury from seafood consumption. Methods: Total mercury (T – Hg) was determined in cord blood from 1869 newborns with birth outcome measures, within the Spanish multicenter INMA cohort from 2004 to 2008. We adjusted cohort speci fi c linear and Cox regression models to evaluate the association between T – Hg and birth anthropometry (weight, length, and head circumference), placental weight and gestational length. Non-spontaneous labor was taken to be censoring in the survival analysis. Final estimates were obtained using meta- analysis. Results: Geometric mean T – Hg was 8.2 μ g/L. A doubling of T – Hg was associated with a 7.7 g decrease in placental weight (95% CI: 13.6, 1.8) and marginally with head circumference (beta: 0.052 cm, 95% CI: 0.109, 0.005). T – Hg was also inversely related to weight and length, although with weaker esti- mates. Mercury exposure was not associated with the length of gestation. The inverse relation between T – Hg and growth was enhanced when the intake of different seafood groups was adjusted for in the models. Conclusions: Prenatal mercury exposure may be associated with reduced placental and fetal growth. Confounding by fish intake should be considered when assessing these relationships. ; This study was funded by Grants from Spain: Instituto de Salud Carlos III (Red INMA G03/176, CB06/02/0041, FIS-FEDER 03/1615, 04/1509, 04/1112, 04/1931, 04/2018, 04/1436, 05/1079, 05/1052, 06/1213, 07/0314, 08/1151, 09/02647, 09/02311, 11/01007, 11/ 02591, 11/02038, 13/1944, 13/02429, 14/00891, 14/01687, and Miguel Servet MS15/0025), Conselleria de Sanitat Generalitat Va- lenciana, Generalitat de Catalunya (CIRIT 1999SGR 00241), De- partment of Health of the Basque Government (2005111093 and 2009111069), the Provincial Government of Gipuzkoa (DFG06/004 and DFG08/001), Obra Social Cajastur and University of Oviedo; and Grants from the EU: NEWGENERIS FP6-2003-Food-3-A- 016320, FP7-ENV-2011 cod 282957, HEALTH.2010.2.4.5-1.