Exposure to Polystyrene Nanoplastics Compromise Ovarian Reserve Function and Endometrial Decidualization in Early Pregnant Mice

ABSTRACT In the environment, nanoplastics (NPs) have been shown to adversely impact reproductive health, yet research on their effects during early pregnancy is scarce. This study investigated the impact of NPs on endometrial decidualization in early pregnant mice and fertility. Female mice were administered polystyrene nanoplastics (PS‐NPs) orally for 90 days before pregnancy. Our findings indicated that PS‐NPs exposure decreased the live birth rate and neonatal crown‐rump length. Decreased embryo implantation sites and uterine wet weight were observed post PS‐NPs exposure. Histological examination revealed structural defects in the uteri of early pregnant mice and a significant reduction in follicular count across all stages in the PS‐NPs‐treated groups. Serum levels of estradiol (E 2 ) and progesterone (P) were elevated, while follicle‐stimulating hormone (FSH) and luteinizing hormone (LH) levels were diminished post‐exposure. Additionally, PS‐NPs exposure upregulated the expression of the endometrial decidualization marker HOXA10 in uterine decidua. In conclusion, our results suggest that exposure to PS‐NPs may disrupt endometrial decidualization during early pregnancy. This disruption is likely due to the perturbation of hormonal balance within the hypothalamic–pituitary–ovary including FSH, LH, E 2 , and P levels. These hormonal alterations may arrest follicular development, consequently leading to detrimental pregnancy outcomes and compromised neonatal birth conditions. Our study provided a new perspective on understanding the possible effects of microplastics on female fertility.