We conducted a cross-sectional study among 194 pregnant women from two low-income settings in Cambodia. The inclusion period lasted from October 2015 through December 2017. Maternal serum samples were analyzed for persistent organic pollutants (POPs). The aim was to study potential effects on birth outcomes. We found low levels of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCP), except for heptachlors, β-hexachlorocyclohexane (HCH), heptachlor epoxide, and p,p’-DDE. There were few differences between the two study locations. However, the women from the poorest areas had significantly higher concentrations of p,p’-DDE (p < 0.001) and hexachlorobenzene (HCB) (p = 0.002). The maternal factors associated with exposure were parity, age, residential area, and educational level. Despite low maternal levels of polychlorinated biphenyls, we found significant negative associations between the PCB congeners 99 (95% CI: −2.51 to −0.07), 138 (95% CI: −1.28 to −0.32), and 153 (95% CI: −1.06 to −0.05) and gestational age. Further, there were significant negative associations between gestational age, birth length, and maternal levels of o,p’-DDE. Moreover, o,p’-DDD had positive associations with birth weight, and both p,p’-DDD and o,p’-DDE were positively associated with the baby’s ponderal index. The poorest population had higher exposure and less favorable outcomes.