Obstetrics and Gynaecology - Theses
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ItemMaternal ophthalmic ultrasound in the assessment of preeclampsia( 2021)The neurological complications of preeclampsia, including eclampsia and intracerebral haemorrhage, are responsible for most of its maternal morbidity and mortality. Treatments are aimed at preventing these cerebral sequelae, and include antihypertensive agents (to prevent intracranial haemorrhage) and magnesium sulphate (for seizure prophylaxis). It is likely that these agents have a direct effect on the maternal cerebrovasculature, although their precise mechanisms of action remain incompletely understood. Ophthalmic ultrasound makes use of the eye’s direct connection to the brain: the ophthalmic artery, which is similar in size and embryological origin to smaller calibre intracerebral vessels, can undergo Doppler interrogation, while the optic nerve sheath diameter (ONSD) can be measured as a marker of intracranial pressure. This thesis aims to assess the utility of ophthalmic ultrasound in the assessment and prediction of preeclampsia, which hitherto has not been performed in an Australian population. In so doing, sonographic assessment of the optic nerve sheath diameter and Doppler variables of the ophthalmic artery was performed in three discrete cohorts: healthy pregnant women (n = 51), pregnant women with suspected but excluded preeclampsia (n = 50), and women with established preeclampsia receiving treatment with the antihypertensive agent labetalol (n = 20) and the anticonvulsant magnesium sulphate (n = 1). In the cohort of healthy pregnant women, the ocular sonographic variables demonstrated no relationship with maternal mean arterial pressure (MAP), gestational age, or each other. Postpartum analysis identified an apparent increase in cerebrovascular resistance – a novel finding. In the cohort of women with suspected but excluded preeclampsia, ocular sonographic variables were not found to differ between those with transient and gestational hypertension on the day of assessment. In contrast to the first cohort, a positive relationship was identified between maternal MAP and the ophthalmic artery peak ratio, and a negative relationship between MAP and the ophthalmic artery pulsatility index. This novel finding is suggestive of greater cerebrovascular susceptibility to changes in systemic blood pressure in women with hypertensive disorders of pregnancy. These two cohorts were combined to assess the utility of ocular sonographic variables in predicting pregnancy outcome. Univariate analysis identified the ophthalmic artery pulsatility/resistive indices and peak ratio as being significantly different in those who went on to develop a sustained hypertensive disorder, whereas the ONSD performed better in multivariate analysis. This was the first study to examine the utility of the ONSD in predicting preeclampsia. Finally, women with established preeclampsia had lower pulsatility indices and higher peak ratios in the ophthalmic artery, and greater dimensions of the optic nerve sheath, than either healthy pregnant women or those with other hypertensive disorders of pregnancy. In a novel finding, administration of labetalol resulted in a shift in the ONSD and Doppler variables of the ophthalmic artery toward those exhibited by healthy pregnant women, which appeared to be independent of labetalol’s effect on systemic blood pressure. Magnesium sulphate appeared to have a similar effect. These observations may permit more precise and individualised care of women with preeclampsia, and thus a reduction in the neurological burden of this disease.