Pregnancy-induced hypertension (PIH), pre-eclampsia, and eclampsia continue to pose significant threats to maternal and perinatal health, particularly in developing countries. These disorders are responsible for a considerable proportion of maternal deaths and fetal complications globally.[1] Severe pre-eclampsia is characterized by rapid clinical deterioration and is frequently associated with serious neurological complications such as eclampsia, intracranial hemorrhage, and cerebral edema, which together account for nearly three-quarters of maternal fatalities in hypertensive disorders of pregnancy.[1,2] The early detection and management of raised intracranial pressure (ICP) in this population are therefore crucial to prevent morbidity and mortality. Advanced imaging techniques, including magnetic resonance imaging (MRI), can reveal signs of focal or generalized cerebral edema in severe pre-eclampsia and eclampsia. [3,4] However, MRI is often impractical for continuous or emergency monitoring due to limited availability, cost, and logistical constraints. Although invasive ICP monitoring remains the gold standard, its application in pregnant women is restricted by safety concerns and procedural complexity. [5] Hence, there is a compelling need for a non-invasive, readily available, and reliable tool to evaluate ICP in obstetric patients. Ocular ultrasonography has emerged as a promising bedside technique for non-invasive ICP estimation. Measurement of the optic nerve sheath diameter (ONSD) using high-frequency ultrasound provides a rapid and reproducible surrogate marker for raised ICP. [6,7] Physiologically, the optic nerve sheath is continuous with the meninges and contains cerebrospinal fluid (CSF) within the subarachnoid space; therefore, any increase in ICP results in a measurable distension of the sheath behind the globe.[5] This correlation has been validated in both neurocritical and obstetric populations, establishing ONSD ultrasonography as a valuable point-of-care tool for the detection of raised ICP. Clinical research supports this association. Dubost et al. demonstrated significantly elevated ONSD values (>5.8 mm) in 20% of women with pre-eclampsia, suggesting subclinical intracranial hypertension. [5] Similarly, Simenc et al. found raised ONSD in 43% of patients with severe pre-eclampsia, further reinforcing its diagnostic utility. [8] Shevlin and Geeraerts et al. also emphasized the clinical accuracy and reproducibility of ONSD measurements for ICP estimation in critical care settings. [6,7] Additionally, Bäuerle et al. confirmed excellent intra- and interobserver reliability of the technique, making it suitable for integration into routine clinical assessment.[10] In pre-eclamptic patients, magnesium sulfate (MgSO₄) therapy remains the cornerstone for seizure prophylaxis and neuroprotection. Beyond its anticonvulsant action, MgSO₄ exerts multiple beneficial effects including vasodilation, stabilization of the blood–brain barrier, and reduction of cerebral edema formation, thereby potentially influencing ICP dynamics. [9,12] Previous studies have documented improved cerebral hemodynamics and reduced vascular resistance following MgSO₄ administration, though its direct impact on ONSD has not been extensively investigated. [9,12] The advent of point-of-care ultrasonography (POCUS) in obstetric anaesthesia has made it feasible to assess ONSD at the bedside within seconds, aiding anaesthesiologists in identifying patients at risk for elevated ICP and in making informed choices between neuraxial and general anaesthesia.[13] By incorporating ultrasonographic ONSD assessment into anaesthetic evaluation protocols, clinicians can prevent catastrophic neurological outcomes while ensuring maternal and fetal safety. The present study was thus designed to evaluate the role of ultrasonography-guided ONSD measurement in parturients with PIH, pre-eclampsia, and eclampsia, and to correlate these findings with disease severity and anaesthetic decision-making. This non-invasive, bedside approach has the potential to enhance anaesthetic safety and optimize outcomes in high-risk obstetric patients.

Study Design and Setting This prospective observational study was conducted in the Department of Anaesthesiology and Obstetrics at a tertiary care centre in Nashik, Maharashtra, over a period of eleven months, from May 2024 to April 2025. The study aimed to evaluate the role of ultrasonography-guided optic nerve sheath diameter (ONSD) measurement in parturients diagnosed with pregnancy-induced hypertension (PIH), pre-eclampsia, and eclampsia, and to correlate the ONSD findings with disease severity for guiding anaesthetic decision-making. Approval for the study was obtained from the Institutional Ethics Committee, and written informed consent was obtained from all participants prior to inclusion. Study Population A total of sixty parturients between 18 and 40 years of age with singleton pregnancies beyond 28 weeks of gestation were enrolled in the study. Participants were divided into four groups based on their clinical diagnosis: Group I – PIH (n = 20), Group II – Pre-eclampsia (n = 20), Group III – Eclampsia (n = 10), and Group IV – Normotensive controls (n = 10). The diagnosis of hypertensive disorders of pregnancy was established according to the American College of Obstetricians and Gynecologists (ACOG) guidelines, which incorporate both clinical and laboratory parameters such as blood pressure measurement, degree of proteinuria, and presence of end-organ dysfunction. Inclusion and Exclusion Criteria Parturients with singleton pregnancies, gestational age of 28 weeks or more, and diagnosed with PIH, pre-eclampsia, or eclampsia were included in the study. Women who were 18 to 40 years old and provided written informed consent were eligible for participation. Patients with known central nervous system disorders, pre-existing ocular diseases (such as glaucoma, optic neuritis, or high myopia), or previous ocular or orbital trauma were excluded. Additionally, patients on medications such as anticonvulsants, sedatives, or diuretics before assessment, or those who declined consent, were not included in the study. Clinical Evaluation All eligible participants underwent a detailed clinical assessment at the time of enrolment. A thorough obstetric and medical history was recorded, followed by general, systemic, and neurological examination. Particular attention was given to symptoms suggestive of raised intracranial pressure such as headache, visual disturbances, altered sensorium, and seizures. Routine laboratory investigations including complete blood count, liver and renal function tests, urine protein estimation, and coagulation profile were carried out. Based on these findings, patients were categorized into PIH, pre-eclampsia, or eclampsia groups as per standard diagnostic criteria. The severity of pre-eclampsia was determined using clinical and biochemical parameters, including blood pressure readings and target organ involvement. Ultrasonographic Technique for ONSD Measurement The optic nerve sheath diameter was measured using a high-frequency (7.5–13 MHz) linear probe attached to a portable ultrasound machine. The procedure was performed by an experienced anaesthesiologist trained in ocular ultrasonography. Each participant was positioned supine with the head in a neutral position and eyes gently closed. A generous amount of sterile ultrasound gel was applied over the closed upper eyelid to avoid exerting pressure on the globe. The ultrasound probe was placed carefully on the upper eyelid, and the optic nerve was visualized as a hypoechoic tubular structure extending posteriorly from the globe. Measurements were taken in both transverse and sagittal planes, and the optic nerve sheath diameter was measured 3 mm posterior to the globe, between the outer borders of the hyperechoic dural sheath. Three readings were obtained from each eye, and the mean value was calculated for analysis. A mean ONSD of more than 5.8 mm was considered indicative of raised intracranial pressure (ICP), in accordance with previously validated reference studies. [5-8] Anaesthetic Assessment and Decision-Making Following ONSD measurement, the anaesthetic plan for each patient was determined based on both clinical and ultrasonographic findings. Parturients with normal ONSD values (≤5.8 mm) and no signs of neurological compromise were considered safe candidates for neuraxial anaesthesia (spinal or epidural). Those with elevated ONSD values (>5.8 mm) or symptoms suggestive of raised ICP were managed under general anaesthesia to prevent the risk of neurological deterioration or herniation. All anaesthetic procedures were performed by the attending anaesthesiologist in consultation with the obstetric team. Intraoperative observations and anaesthetic decisions were documented for each participant. Intraoperative and Postoperative Monitoring Intraoperative monitoring included continuous recording of maternal heart rate, blood pressure, oxygen saturation (SpO₂), and end-tidal carbon dioxide (EtCO₂). Any intraoperative complications such as hypotension, desaturation, seizures, or unresponsiveness were documented. Neonatal outcomes were assessed using Apgar scores at one and five minutes post-delivery. Following surgery, all parturients were monitored for at least 24 hours postoperatively for neurological symptoms such as persistent headache, visual disturbances, or altered mental status. Any adverse maternal or fetal events were recorded. Data Collection and Statistical Analysis All relevant demographic, clinical, and ultrasonographic data were entered in a predesigned proforma and later compiled in a master chart for analysis. Statistical analysis was performed using SPSS version 28. Continuous variables were presented as mean ± standard deviation (SD), while categorical variables were expressed as frequency and percentage. The differences in mean ONSD values among the four study groups were analyzed using one-way analysis of variance (ANOVA) for normally distributed data and the Kruskal–Wallis test for non-parametric data. Correlations between ONSD and disease severity, neurological symptoms, and anaesthetic choice were assessed using Pearson’s or Spearman’s correlation coefficients as applicable. A p-value <0.05 was considered statistically significant.

Table 1: Demographic and Clinical Characteristics of Study Participants Parameter Normotensive Controls (n=10) PIH (n=20) Pre-eclampsia (n=20) Eclampsia (n=10) p-value Age (years, Mean ± SD) 26.1 ± 3.2 25.9 ± 3.6 26.5 ± 3.9 25.8 ± 4.1 0.88 Gestational age (weeks, Mean ± SD) 35.4 ± 2.1 34.9 ± 2.5 33.7 ± 3.0 33.1 ± 2.8 0.07 BMI (kg/m², Mean ± SD) 25.3 ± 2.1 26.5 ± 2.4 27.2 ± 2.7 27.5 ± 2.6 0.19 Primigravida, n (%) 5 (50%) 10 (50%) 11 (55%) 6 (60%) 0.91 Systolic BP (mm Hg, Mean ± SD) 118.3 ± 9.8 148.5 ± 12.2 162.6 ± 15.8 173.4 ± 17.6 <0.001* Diastolic BP (mm Hg, Mean ± SD) 75.9 ± 7.4 93.2 ± 8.5 104.5 ± 10.1 110.6 ± 12.4 <0.001* Headache, n (%) 0 (0%) 4 (20%) 11 (55%) 8 (80%) <0.001* Visual disturbance, n (%) 0 (0%) 2 (10%) 7 (35%) 6 (60%) <0.001* Altered sensorium / seizure, n (%) 0 (0%) 0 (0%) 2 (10%) 10 (100%) <0.001* *Significant at p < 0.05. The mean age of participants ranged from 25.8 ± 4.1 to 26.5 ± 3.9 years across all groups, with no significant difference (p = 0.88). The mean gestational age was lowest in the eclampsia group (33.1 ± 2.8 weeks) and highest among controls (35.4 ± 2.1 weeks) (p = 0.07). The BMI values ranged between 25.3 ± 2.1 kg/m² in controls and 27.5 ± 2.6 kg/m² in the eclampsia group (p = 0.19). Half of the participants in the PIH group and 60% in the eclampsia group were primigravidas (p = 0.91). The mean systolic blood pressure increased progressively from 118.3 ± 9.8 mm Hg in controls to 173.4 ± 17.6 mm Hg in eclampsia, while mean diastolic pressure rose from 75.9 ± 7.4 mm Hg to 110.6 ± 12.4 mm Hg (both p < 0.001). The frequency of headache was 0%, 20%, 55%, and 80% across control, PIH, pre-eclampsia, and eclampsia groups, respectively. Visual disturbances were reported in 0%, 10%, 35%, and 60% of the same groups, and altered sensorium or seizures occurred exclusively in the eclampsia group (100%) (p < 0.001 for all). Table 2: Comparison of Mean Optic Nerve Sheath Diameter (ONSD) Across Study Groups Group Right Eye (mm, Mean ± SD) Left Eye (mm, Mean ± SD) Mean Bilateral ONSD (mm, Mean ± SD) Participants with ONSD > 5.8 mm, n (%) Normotensive Controls (n=10) 4.85 ± 0.36 4.80 ± 0.32 4.83 ± 0.31 0 (0%) PIH (n=20) 5.12 ± 0.41 5.10 ± 0.37 5.11 ± 0.39 2 (10%) Pre-eclampsia (n=20) 5.91 ± 0.58 5.86 ± 0.55 5.89 ± 0.56 12 (60%) Eclampsia (n=10) 6.22 ± 0.61 6.15 ± 0.64 6.18 ± 0.62 8 (80%) p-value <0.001* <0.001* <0.001* — *Significant at p < 0.05. Post-hoc Tukey analysis showed significant differences between controls ↔ pre-eclampsia (p<0.001) and controls ↔ eclampsia (p<0.001), but not between PIH ↔ controls (p=0.12). The mean right-eye ONSD ranged from 4.85 ± 0.36 mm in normotensive controls to 6.22 ± 0.61 mm in the eclampsia group, while the left-eye ONSD ranged from 4.80 ± 0.32 mm to 6.15 ± 0.64 mm. The mean bilateral ONSD values progressively increased from 4.83 ± 0.31 mm in controls, 5.11 ± 0.39 mm in PIH, 5.89 ± 0.56 mm in pre-eclampsia, to 6.18 ± 0.62 mm in eclampsia. Participants with ONSD > 5.8 mm were observed in 0% of controls, 10% of the PIH group, 60% of the pre-eclampsia group, and 80% of the eclampsia group. The difference in mean ONSD across groups was highly significant (p < 0.001), with post-hoc analysis revealing significant differences between controls and both pre-eclampsia and eclampsia groups, but not between PIH and controls. Table 4: Distribution of Anaesthetic Techniques According to ONSD Findings ONSD Status n (%) Anaesthetic Technique n (%) Intraoperative Complications n (%) ONSD ≤ 5.8 mm 38 (63.3%) Neuraxial (spinal/epidural) 35 (92.1%) Mild hypotension 4 (10.5%) ONSD > 5.8 mm 22 (36.7%) General anaesthesia 15 (68.2%) Desaturation / agitation 3 (13.6%) _______ _______ Neuraxial avoided due to raised ICP 7 (31.8%) None significant — Among the 60 parturients, 38 (63.3%) had ONSD ≤ 5.8 mm, and 22 (36.7%) showed ONSD > 5.8 mm. Of those with normal ONSD, 35 patients (92.1%) received neuraxial anaesthesia (spinal or epidural), with mild hypotension observed in 4 cases (10.5%). In contrast, among patients with raised ONSD, 15 (68.2%) were managed under general anaesthesia, while 7 (31.8%) were deemed unsuitable for neuraxial anaesthesia due to suspected raised intracranial pressure. Intraoperative desaturation or agitation occurred in 3 patients (13.6%) from the raised ONSD group, while no major complications were reported in the rest. Table 5: Maternal and Fetal Outcomes Outcome Parameter Normotensive Controls (n=10) PIH (n=20) Pre-eclampsia (n=20) Eclampsia (n=10) p-value Mode of delivery – Cesarean section, n (%) 3 (30%) 8 (40%) 14 (70%) 9 (90%) <0.001* Duration of surgery (min, Mean ± SD) 47.6 ± 10.2 50.1 ± 9.8 55.4 ± 11.7 59.2 ± 12.3 0.04* Intraoperative complications, n (%) 0 (0%) 1 (5%) 3 (15%) 2 (20%) 0.09 Postoperative headache (VAS > 3), n (%) 0 (0%) 2 (10%) 6 (30%) 5 (50%) <0.001* Neonatal Apgar score < 7 (1 min), n (%) 0 (0%) 1 (5%) 3 (15%) 3 (30%) 0.03* Mean birth weight (kg, Mean ± SD) 2.91 ± 0.36 2.70 ± 0.32 2.54 ± 0.28 2.32 ± 0.30 0.001* *Significant at p < 0.05. The rate of cesarean section increased progressively across groups, from 30% in normotensive controls to 90% in eclampsia cases (p < 0.001). The mean duration of surgery was longest in the eclampsia group (59.2 ± 12.3 minutes) and shortest among controls (47.6 ± 10.2 minutes) (p = 0.04). Intraoperative complications occurred in 0%, 5%, 15%, and 20% of controls, PIH, pre-eclampsia, and eclampsia groups respectively (p = 0.09). Postoperative headache (VAS > 3) was reported in 0% of controls, 10% of PIH, 30% of pre-eclampsia, and 50% of eclampsia patients (p < 0.001). Neonatal Apgar scores below 7 at 1 minute were observed in 0%, 5%, 15%, and 30% of the respective groups (p = 0.03). The mean birth weight decreased progressively with disease severity, ranging from 2.91 ± 0.36 kg in controls to 2.32 ± 0.30 kg in the eclampsia group (p = 0.001).

In this prospective observational study conducted at a tertiary care centre in Nashik over 11 months, we observed a progressive increase in mean optic nerve sheath diameter (ONSD) from normotensive controls to patients with eclampsia. Parturients with mean ONSD > 5.8 mm had a higher frequency of neurological manifestations and required general anaesthesia more frequently compared to those with normal ONSD. These findings suggest that ONSD, measured non-invasively using ultrasonography, may serve as a reliable surrogate marker of raised intracranial pressure (ICP) in parturients with hypertensive disorders of pregnancy and may guide anaesthetic decision-making. Our findings are consistent with previous research showing significantly increased ONSD values in women with pre-eclampsia. Dubost et al. reported that 19% of pre-eclamptic women had ONSD > 5.8 mm, indicating subclinical intracranial hypertension [14]. Similarly, Simenc et al. found raised ONSD (> 5.8 mm) in 43% of patients with severe pre-eclampsia [15]. In our cohort, 60% of pre-eclamptic and 80% of eclamptic parturients demonstrated ONSD values above this threshold, reinforcing the association between ONSD and disease severity. These elevated ONSD values likely reflect increased ICP due to cerebral oedema and altered autoregulation — key neuropathophysiological mechanisms of severe pre-eclampsia [16, 17]. A similar trend was reported by Sterrett et al., who observed significantly higher ONSD in women with pre-eclampsia accompanied by neurological features compared with normotensive controls [18]. Moreover, Rajajee et al. and Geeraerts et al. validated the strong correlation between ONSD and invasively measured ICP in neurocritical patients [19, 20]. These findings collectively support the use of ONSD as a quantitative, bedside indicator of raised ICP in obstetric populations. Pathophysiological Correlation The optic nerve sheath is an extension of the meninges and is continuous with the intracranial subarachnoid space; hence, any increase in cerebrospinal fluid (CSF) pressure is transmitted along the sheath, resulting in distension that can be detected ultrasonographically [19]. This principle forms the physiological rationale for using ONSD as a marker of raised ICP. In our study, ONSD correlated positively with mean arterial pressure and with neurological symptoms such as headache, visual disturbances, and altered sensorium, consistent with the findings of Bäuerle et al. [21], who demonstrated that ONSD measurements are reproducible and closely reflect dynamic ICP changes. Effect of Magnesium Sulphate Therapy In the present study, although the mean ONSD values decreased slightly in pre-eclamptic and eclamptic women after magnesium sulphate (MgSO₄) administration, the reduction was not statistically significant. This finding is in line with the observations of Assu et al., who reported a non-significant decline in ONSD after MgSO₄ therapy despite marked improvement in neurological symptoms [22]. However, Elkarmal et al. found a significant reduction in ONSD following MgSO₄ treatment in severe pre-eclampsia, suggesting that magnesium’s vasodilatory and neuroprotective effects may decrease cerebral oedema and intracranial tension [23]. These differences could be attributed to variations in baseline disease severity, timing of ONSD measurement, and the ultrasonographic methodology used across studies. Clinical Implications for Anaesthetic Management From an anaesthetic perspective, the assessment of ONSD can assist in determining the safety of neuraxial anaesthesia in patients with hypertensive disorders of pregnancy. Raised ICP is considered a relative contraindication for spinal or epidural anaesthesia due to the potential risk of brainstem herniation. In our study, patients with ONSD > 5.8 mm were managed under general anaesthesia, while those with normal ONSD underwent neuraxial techniques without complications. This observation aligns with the growing evidence that point-of-care ultrasonography can enhance clinical decision-making in obstetric anaesthesia by identifying high-risk patients early [20, 22]. Strengths and Limitations The strengths of this study include its prospective design, inclusion of a wide spectrum of hypertensive disorders, and real-time clinical correlation of ONSD with anaesthetic outcomes. However, limitations include the absence of invasive ICP monitoring (the gold standard), single-centre design, and relatively small sample size. Additionally, inter-observer variability in ONSD measurement could influence reproducibility, although the use of standardized technique and single-operator scanning minimized this limitation. Future Directions Future multicentric studies with larger cohorts and standardized ultrasound techniques are warranted to establish ONSD reference values in pregnant populations and to validate its role in anaesthetic planning. Integrating ONSD measurement with other non-invasive tools, such as transcranial Doppler, may provide comprehensive insights into cerebrovascular dynamics in pre-eclampsia and eclampsia.

In summary, the findings of this study support the utility of ultrasonography-guided ONSD measurement as a simple, non-invasive, and reproducible bedside tool for the early detection of raised ICP in hypertensive disorders of pregnancy. Elevated ONSD values correlate with disease severity and neurological symptoms and can guide anaesthetic decision-making to improve maternal and fetal outcomes

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