The aim of the study was to analyze the association between prenatal environmental tobacco smoke exposure (ETS) and child anthropometric parameters at birth such birth weight, length, head and chest circumference. The study population consisted of 107 pregnant women from Lodz district as the part of Polish Mother and Child Cohort study. The child prenatal ETS exposure was assessed based on questionnaire with mothers and cotinine level in saliva collected three times in pregnancy. The level of cotinine in biological samples was analyzed using liquid chromatography with tandem mass spectrometry (LC-MS/MS ESI+). About 35% of the children were prenatally exposed to ETS. The birth weight of the children prenatally exposed to ETS was 335 g lower than the birth weight of non-exposed newborns p < 0.001 after adjustment for: maternal educational level, marital status, prepregnancy weight, child gender, and gestational age. The same refers to child length and chest circumference (coef. -1.1 cm; p = 0.03 and coef. -1.3 cm; p = 0.002 respectively). Taking into account the negative effect of prenatal exposure to ETS, more efforts need to be taken to eliminate child ETS exposure.