Imaging putative foetal cerebral blood oxygenation using susceptibility weighted imaging (SWI)

To evaluate the magnetic susceptibility, ∆χ _v , as a surrogate marker of venous blood oxygen saturation, S _v O ₂, in second- and third-trimester normal human foetuses.

Thirty-six pregnant women, having a mean gestational age (GA) of 31 2/7 weeks, underwent magnetic resonance imaging (MRI). Susceptibility-weighted imaging (SWI) data from the foetal brain were acquired. ∆χ _v of the superior sagittal sinus (SSS) was quantified using MR susceptometry from the intra-vascular phase measurements. Assuming the magnetic property of foetal blood, ∆χ _do , is the same as that of adult blood, S _v O ₂ was derived from the measured Δχ _v . The variation of ∆χ _v and S _v O ₂, as a function of GA, was statistically evaluated.

The mean ∆χ _v in the SSS in the second-trimester (n = 8) and third-trimester foetuses (n = 28) was found to be 0.34± 0.06 ppm and 0.49 ±0.05 ppm, respectively. Correspondingly, the derived S _v O ₂ values were 69.4% ±3.27% and 62.6% ±3.25%. Although not statistically significant, an increasing trend (p = 0.08) in Δχ _v and a decreasing trend (p = 0.22) in S _v O ₂ with respect to advancing gestation was observed.

We report cerebral venous blood magnetic susceptibility and putative oxygen saturation in healthy human foetuses. Cerebral oxygen saturation in healthy human foetuses, despite a slight decreasing trend, does not change significantly with advancing gestation.

• Cerebral venous magnetic susceptibility and oxygenation in human foetuses can be quantified. • Cerebral venous oxygenation was not different between second- and third-trimester foetuses. • Foetal cerebral venous oxygenation does not change significantly with advancing gestation.