Abstract : Background: The poor newborn outcomes of breastfeeding during pregnancy have not been clearly established. The aim of this study was to determine poor newborn outcomes of breastfeeding during pregnancy. Methods: A meta-analysis was undertaken to review current studies related to poor newborn outcomes of breastfeeding during pregnancy. A search of PubMed, and ProQuest for related articles published (January 2000 until November 2022). The pooled mean difference from the acquired data were calculated with a 95% CI. The fixed and random effects analysis was performed. The results were presented as forest plots, and Egger's test was used to examine study bias. Review Manager (RevMan) 5.4 and STATA 14.2 were used to process and analyze all of the data. Results: Breastfeeding during pregnancy is not related to the baby's body length (p>0.05). However, there was an association during breastfeeding pregnancy with birth weight, where the difference in birth weight between the case and control groups was -251.36 gr (95% CI - 701.51-198.79 gr). The heterogeneity analysis revealed heterogeneous in birth weight outcomes of breastfeeding during pregnancy (I2 > 50%). Conclusion: There was an association during breastfeeding pregnancy with birth weight. This study can provide input in the preventing and promoting management to reduce the poor prognosis during pregnancy.