Department of Clinical and Experimental Medicine, University of Pisa, 56126 Pisa, Italy.
Neonatology Unit, Azienda Ospedaliero-Universitaria Pisana, 56126 Pisa, Italy.
Int J Mol Sci. 2023 Aug 6;24(15):12487. doi: 10.3390/ijms241512487.
The embryo and fetus grow in a hypoxic environment. Intrauterine oxygen levels fluctuate throughout the pregnancy, allowing the oxygen to modulate apparently contradictory functions, such as the expansion of stemness but also differentiation. We have recently demonstrated that in the last weeks of pregnancy, oxygenation progressively increases, but the trend of oxygen levels during the previous weeks remains to be clarified. In the present retrospective study, umbilical venous and arterial oxygen levels, fetal oxygen extraction, oxygen content, CO, and lactate were evaluated in a cohort of healthy newborns with gestational age < 37 weeks. A progressive decrease in pO levels associated with a concomitant increase in pCO and reduction in pH has been observed starting from the 23rd week until approximately the 33-34th week of gestation. Over this period, despite the increased hypoxemia, oxygen content remains stable thanks to increasing hemoglobin concentration, which allows the fetus to become more hypoxemic but not more hypoxic. Starting from the 33-34th week, fetal oxygenation increases and ideally continues following the trend recently described in term fetuses. The present study confirms that oxygenation during intrauterine life continues to vary even after placenta development, showing a clear biphasic trend. Fetuses, in fact, from mid-gestation to near-term, become progressively more hypoxemic. However, starting from the 33-34th week, oxygenation progressively increases until birth. In this regard, our data suggest that the placenta is the hub that ensures this variable oxygen availability to the fetus, and we speculate that this biphasic trend is functional for the promotion, in specific tissues and at specific times, of stemness and intrauterine differentiation.
胚胎和胎儿在缺氧环境中生长。子宫内的氧气水平在整个孕期内波动，使氧气能够调节明显矛盾的功能，如干细胞的扩张和分化。我们最近表明，在妊娠的最后几周，氧合作用逐渐增加，但前几周的氧气水平趋势仍有待澄清。在本回顾性研究中，我们评估了一组胎龄<37 周的健康新生儿的脐静脉和动脉氧水平、胎儿氧摄取、氧含量、CO 和乳酸。从第 23 周到大约 33-34 孕周，观察到 pO 水平逐渐下降，同时 pCO 增加，pH 值降低。在此期间，尽管出现了更严重的低氧血症，但由于血红蛋白浓度的增加，氧含量保持稳定，这使胎儿变得更缺氧但不更缺氧。从第 33-34 孕周开始，胎儿氧合作用增加，并且理想情况下会继续遵循最近在足月胎儿中描述的趋势。本研究证实，即使在胎盘发育后，胎儿在宫内的氧合作用仍在继续变化，表现出明显的双相趋势。事实上，从中孕期到近足月，胎儿逐渐变得更缺氧。然而，从第 33-34 孕周开始，氧合作用逐渐增加，直到出生。在这方面，我们的数据表明胎盘是确保胎儿获得这种可变氧气供应的中心，我们推测这种双相趋势对于促进特定组织和特定时间的干细胞特性和宫内分化是功能性的。
