Ovine fetal umbilical artery Doppler systolic diastolic ratios and nitric oxide synthase

Doppler analysis and placental nitric oxide synthase expression during fetal growth restriction

OBJECTIVE

To assess placental nitric oxide (NO) metabolism related to changes in the uteroplacental circulation during fetal growth restriction (FGR).

METHODS

The resistance index (RI) from the uterine arteries and pulsatility index (PI) from the umbilical artery were determined by Doppler analysis in 15 patients with FGR and 12 healthy controls, before elective cesarean section. Inducible (iNOS) and endothelial (eNOS) NO synthase expression were measured in placental samples. Immunohistochemistry was performed for iNOS location in the placenta.

RESULTS

During FGR, we observed a significant elevation of iNOS when compared with controls. Conversely, eNOS did not differ between the two groups. A negative correlation with eNOS (r = -0.85) and a positive correlation with iNOS (r = 0.91) was found correlating to umbilical PI. The iNOS proteins were reduced in syncytiotrophoblast cells and increased in endothelium in the FGR group compared to the controls.

CONCLUSIONS

During FGR, placental iNOS expression is significantly increased; this increase possibly represents an adaptive physiological mechanism for overcoming a fetoplacental circulation deficiency.

Vascular Doppler techniques

Doppler ultrasound used for the assessment of the fetal umbilical circulation in the human pregnancy has been reported in the scientific literature since the early 1980s and has been rigorously evaluated by randomized, controlled trials. The consensus of the reviewers of these trials is that there do appear to be grounds for including umbilical artery Doppler ultrasound studies in the management of high-risk pregnancies. There is no apparent benefit for low-risk pregnancies or later gestation. Other fetal vascular beds are currently undergoing prospective studies and some limited randomized, controlled trials have been reported; but to date they are not at a point of development to be considered part of clinical management.