Objectives: Because previous analyses of prenatal care (PNC) utilization and risk of low birth weight (LBW) may have been influenced by selection bias, we conducted a study using longitudinal data of women with repeat pregnancies. Methods: We analyzed Washington State birth certificates of first and second live births (2003-2012). We estimated relative risk (RR) of LBW at second birth associated with Kotelchuck Index PNC level among women stratified by level of PNC in their first birth (n = 67,571). Results: Among women with inadequate PNC prior to their first birth (n = 10,355), women with intermediate or adequate PNC before their second birth (n = 7464) had a reduced risk of LBW (adjusted RR 0.61, 95 % CI: 0.48, 0.78) compared to those whose PNC level remained inadequate. Likewise, among women with intermediate or adequate PNC prior to their first birth (n = 57,216), those with inadequate PNC before the second birth (n = 7095) had higher risk of LBW (adjusted RR 1.59, 95 % CI: 1.36, 1.85) compared to those who remained at intermediate or adequate PNC. Conclusions: Our findings support the hypothesis that PNC decreases LBW risk at second birth, independent of factors related to the utilization of PNC at first birth.