Aim We measured the frequency of nuclear abnormalities of 210 blood samples from the umbilical cord, since human fetuses are exposed to environmental mixtures of pesticides that induce DNA damage. Methods The determinations were made through the micronucleus assay test in lymphocytes from the umbilical cord blood of newborns whose mothers live in Ahome (n = 105) and Guasave (n = 105), Sinaloa, Mexico. Results The average frequency of anomalies in 1000 cells were, respectively: micronucleus 0.4 vs. 2.9, pyknotic cells 18.3 vs. 109.2, chromatin condensation 7.7 vs. 150.1, karyolitic cells 1.8 vs. 24.4, and binucleated cells 4.9 vs. 74.6. The calculated Pearson correlation factors of nuclear abnormality frequencies between both municipalities were low and negative, suggesting that they did not correlate between the Ahome and Guasave newborns and indicating a higher number of mothers exposed in Guasave. Conclusion Our data suggest that monitoring nuclear abnormalities in umbilical cord blood samples could be a useful tool to identify transplacental mutagens perfusion that is being discharged into the local environment.