Benzene-induced growth restriction and compensatory rebound in mouse fetuses and placentas

Benzene is a ubiquitous environmental toxicant and carcinogen, yet its effects on early placental and fetal development remain poorly defined. In our previous work, repeated mid-gestation benzene exposure increased fetal and placental size at gestational day (GD) 19, indicating compensatory growth responses. Here, we investigated the immediate consequences of the same exposure paradigm to determine how these effects unfold over time. Pregnant CD-1 mice received intraperitoneal injections (200 mg/kg) of either benzene or a vehicle control on GD8, 10, 12, and 14, and fetal and placental outcomes were assessed at 2, 6, and 24 h after the final exposure. Benzene exposure initially reduced fetal and placental weight, which then increased over time and surpassed control values by 24 h. These growth dynamics were influenced by both sex and uterine position: males exhibited early growth deficits, while females showed delayed compensatory responses; fetuses in the left uterine horn were disproportionately growth-restricted at 2 h, though this difference was not evident at later timepoints. Together with our GD19 findings, these results define a growth trajectory in which in utero benzene exposure first restricts fetal and placental development, followed by rebound growth that ultimately exceeds control levels. These findings demonstrate that susceptibility to benzene is modified by intra-litter variables, with sex- and horn-specific factors contributing to variability in outcome. This work underscores the importance of accounting for intra-litter variability when evaluating developmental toxicants and highlights the need for future studies into the mechanisms driving rebound growth responses.