(362) A two-hit model: Impact of maternal Hypoxia on IVF-Derived Pregnancies

Reza K. Oqani¹, Emin Maltepe¹, Paolo Rinaudo¹ and Daniel E. Wagner¹

¹University of California San Francisco, San Francisco, CA

Abstract Text:

Background:

IVF pregnancies have been linked to higher risks of fetal growth restriction, preeclampsia, and placental insufficiency, yet the mechanisms underlying these vulnerabilities remain unclear. The placenta must adapt to environmental stressors such as maternal hypoxia, which can impair fetal development. Given that our transcriptomic analysis identified upregulation of hypoxia-responsive genes in IVF placentas, we investigated whether IVF embryos exhibit increased sensitivity to hypoxic stress in vivo.

Methods:

IVF conceptuses were generated by superovulating CF-1 female mice with PMSG (5 IU) followed by hCG (5 IU) 48 hours later, then retrieving MII oocytes from ampullae. Sperm were collected from B6D2F1 males, capacitated in HTF medium, and co-incubated with oocytes for 4 hours. Zygotes were cultured in KSOMaa medium until the blastocyst stage. For the FB control group, naturally fertilized E3.5 blastocysts were collected from superovulated CD-1 females mated with B6D2F1 males.

Pregnant dams carrying IVF- and FB-conceived embryos were exposed to normoxia (21% O₂) or hypoxia (10.5% O₂) conditions from E7.5 to E12.5. Pregnancy loss, fetal and placental weights, and transcriptomic changes were assessed. snRNA-seq was performed to examine hypoxia-induced gene expression changes, followed by DESeq2 analysis and GO/KEGG pathway enrichment.

Results:

Under normoxic conditions, IVF placentas were significantly larger than FB controls (119.8 ± 4.1 mg vs. 108.7 ± 3.2 mg, p < 0.05), while fetal weights were lower (120.5 ± 4.7 mg vs. 133.4 ± 5.1 mg, p < 0.05), leading to a higher placental-to-fetal weight ratio (P/F) in IVF embryos (0.99 ± 0.03 vs. 0.81 ± 0.02, p < 0.01).

Following hypoxia exposure, placental weights decreased in both groups, but IVF placentas lost their relative size advantage (96.1 ± 4.6 mg in IVF vs. 94.5 ± 3.8 mg in FB, p = ns). Fetal weights were significantly reduced in both groups, but the decrease was more pronounced in IVF conceptuses (98.2 ± 5.0 mg in IVF vs. 110.3 ± 4.2 mg in FB, p < 0.05). As a result, the P/F ratio remained elevated in IVF pregnancies under hypoxia (0.98 ± 0.04 vs. 0.86 ± 0.03, p < 0.05), indicating impaired placental efficiency.

Hypoxia also resulted in higher pregnancy loss in IVF embryos, with IVF dams exhibiting an average of 4.0 ± 0.8 abortive sites per litter compared to 1.3 ± 0.5 in FB controls (p < 0.01).

Conclusion:

IVF-derived conceptuses are more vulnerable to maternal hypoxia compared to naturally conceived conceptuses, resulting in higher pregnancy loss and altered placenta fetal ratio. This study provides strong evidence that IVF conception have reduced ability to adapt to a second stressor (as postulated by a DOHaD two hit model), in this case represented by maternal oxygen availability during pregnancy. These findings underscore the importance of refining IVF protocols and identifying potential interventions to improve placental function and fetal health in ART-conceived pregnancies.