OPHthalmic artEry DoppLer Evaluation After 37 Weeks of Gestation and Intrapartum Fetal Adverse Outcomes (the OPHELIA Study)

The ophthalmic artery (OA) Doppler has been recently proposed as a potential "soft marker" for placental insufficiency in retrospective and observational studies, with similar clinical significance with respect to Uterine Artery (UA) Doppler evaluation. It has been investigated in small-for-gestational-age (SGA) or fetal-growth-restricted (FGR) fetuses, as well as in low-risk pregnancies and at various gestational ages during pregnancy, showing to be predictive of impaired placentation, and, consequently, of pre-eclampsia occurrence.

The OA is the first branch of the internal carotid artery and its Doppler velocity waveform has two systolic peaks. The first systolic wave (PSV1) is created by cardiac systole, with the opening of the aortic valve and ejection of blood into the aorta, whilst the second systolic wave (PSV2) is a reflective wave formed by the systolic pulse wave reaching smaller, higher resistance arterioles and being reflected back towards the heart. At the level of the aortic arch, a fraction is diverted cranially to the cerebral circulation as a forward wave to create PSV2. In this way, PSV2 is most influenced by peripheral arterial compliance and resistance, whilst PSV1 is more affected by cardiac output. Therefore, an increase in the ratio of PSV2 to PSV1 (PSV ratio) could represent an increase in peripheral vascular resistance and/or a reduction in cardiac output, which are both indirect signs of placental dysfunction. The latter can be manifested during labor with well-established cardiotocographic patterns and induction of labor, alone, may enhance the intrapartum hypoxic stress on the fetus.

Furthermore, another parameter that is currently understudy is the Optic Nerve Sheath Diameter (ONSD). Recent evidence suggests that ONSD increases in pre-eclamptic patients, possibly reflecting a transient increase in intracranial pressure. However, evidence is scarce regarding its physiologic changes during and after labour. In understanding the potential mechanisms behind intrapartum fetal compromise in gravid, at-term patients undergoing labor induction, the hypothesis is that placental dysfunction, albeit not necessarily clinically manifest earlier in pregnancy, may play a role in fetal compromise during labor, especially in pregnancies undergoing induction of labor. Hence, investigating potential associations between a "soft marker" of placental insufficiency as Ophthalmic artery Doppler PSV ratio alterations and intrapartum fetal compromise would be paramount. Therefore the aim of this prospective interventional study is to investigate any association with altered OA PSV ratio and intrapartum fetal adverse outcomes in pregnant patients that reach term of pregnancy, undergoing induction of labor. In addition, the investigatos also aim to evaluate the ONSD before and after the second stage of labour in order to study its physiologic changes.