Response to 'Commentary on the published position statement regarding the pathogenesis of fetal basal ganglia- thalamic hypoxic-ischaemic injury' (Anthony et al.)

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Trisomy 21 screening with αlpha software and the Fetal Medicine Foundation algorithm

BACKGROUND

Screening for trisomy 21 provides pregnant women with accurate risk information. Different algorithms are used to screen for trisomy 21 in South Africa (SA). The Fetal Medicine Foundation (FMF) provides software to screen for trisomy 21 in the first trimester by ultrasound or a combination of ultrasound and biochemistry (combined screening), and requires regular and stringent quality control. With αlpha software, first trimester combined screening and screening with biochemistry alone in the first or second trimester are possible. The αlpha screening requires quality control of biochemical tests, but not of ultrasound measurements. Ideally, a screening test should have a high detection and a low screen positive rate. Despite the availability of these screening programmes, only a minority of infants with trisomy 21 are detected prenatally, raising questions about the effectiveness of screening.

OBJECTIVES

To determine the screen positive and detection rates of prenatal screening for trisomy 21 in the SA private healthcare system.

METHODS

Data from the three largest laboratories collected between 2010 and 2015 were linked with genetic tests to assess screen positive and detection rates. Biochemical screening alone with αlpha software (first or second trimester) and combined screening using either FMF or αlpha software were compared.

RESULTS

One-third of an estimated 675 000 pregnancies in private practice in the 6-year study period underwent screening. There were 687 cases of trisomy 21 in 225 021 pregnancies, with only 239 (35%) diagnosed prenatally. The screen positive rates were 11.8% for first trimester biochemistry, 7.6% for second trimester biochemistry, 7.3% for first trimester FMF software ultrasound alone, 3.7% for combined first trimester screening with FMF software, and 3.5% for combined first trimester screening with αlpha software. The detection rates for a 5% false positive rate were 63% for first trimester biochemistry, 69% for second trimester biochemistry, 95% for combined first trimester screening with FMF software and 80% for combined first trimester screening with αlpha software. Detection and confirmation rates were highest with FMF software.

CONCLUSION

Screening with FMF software has a similar screen positive rate and better detection rate than screening with αlpha software. The low prenatal detection rate of trisomy 21 is mainly due to a low prevalence of screening. More research is needed in the SA setting to explore why screening and confirmatory testing after high-risk results are not performed in many pregnancies.

Clinical practice

Basal ganglia and thalamus (BGT) hypoxic-ischaemic brain injury is currently the most contentious issue in cerebral palsy (CP) litigation in South Africa (SA), and merits a consensus response based on the current available international literature. BGT pattern injury is strongly associated with a preceding perinatal sentinel event (PSE), which has a sudden onset and is typically unforeseen and unpreventable. Antepartum pathologies may result in fetal priming, leading to vulnerability to BGT injury by relatively mild hypoxic insults. BGT injury may uncommonly follow a gradual-onset fetal heart rate deterioration pattern, of duration ≥1 hour. To prevent BGT injury in a clinical setting, the interval from onset of PSE to delivery must be short, as little as 10 - 20 minutes. This is difficult to achieve in any circumstances in SA. Each case needs holistic, multidisciplinary, unbiased review of all available antepartum, intrapartum and postpartum and childhood information, aiming at fair resolution without waste of time and resources.

Cerebral palsy and its medicolegal implications in low- resource settings - the need to establish causality and revise criteria to implicate intrapartum hypoxia: A narrative review

The objective of this study was to establish scientific causality and to devise criteria to implicate intrapartum hypoxia in cerebral palsy (CP) in low-resource settings, where there is potential for an increase in damaging medicolegal claims against obstetric caregivers, as is currently the situation in South Africa. For the purposes of this narrative review, an extensive literature search was performed, including any research articles, randomised controlled trials, observational studies, case reports or expert or consensus statements pertaining to CP in low-resource settings, medicolegal implications, causality, and criteria implicating intrapartum hypoxia. In terms of causation, there are differences between high-income countries (HICs) and low-resource settings. While intrapartum hypoxia accounts for 10 - 14% of CP in HICs, the figure is higher in low-resource settings (20 - 46%), indicating a need for improved intrapartum care. Criteria implicating intrapartum hypoxia presented for HICs may not apply to low-resource settings, as cord blood pH testing, neonatal brain magnetic resonance imaging (MRI) and placental histology are frequently not available, compounded by incomplete clinical notes and missing cardiotocography tracings. Revised criteria in an algorithm for low-resource settings to implicate intrapartum hypoxia in neonatal encephalopathy (NE)/ CP are presented. The algorithm relies first on specialist neurological assessment of the child, determination of the occurrence of neonatal encephalopathy (by documented or verbal accounts) and findings on childhood MRI, and second on evidence of antepartum and intrapartum contributors to the apparent hypoxia-related CP. The review explores differences between low-resource settings and HICs in trying to establish causation in NE/CP and presents a revised scientific approach to causality in the context of low-resource settings for reaching appropriate legal judgments.

The clinical prognostic significance of myocardial performance index (MPI) in stable placental-mediated disease

AIM

To determine whether a single elevated myocardial performance index (MPI) value in the third trimester of pregnancy is a marker for later adverse obstetric outcomes in stable placental-mediated disease, defined as well-controlled pre-eclampsia (PE) on a single agent and/or uncompensated intra-uterine growth restriction (IUGR).

METHODS

Fifty-five foetuses whose mothers had stable placental-mediated disease, either mild pre-eclampsia controlled on a single agent, and/or uncompensated IUGR in the third trimester, attending the Foetal Unit at Inkosi Albert Luthuli Hospital, Durban, South Africa were prospectively recruited with 55 matched controls. Recorded data for the subjects included demographic data of maternal age and parity, sonographic data of estimated foetal weight (EFW) and amniotic fluid index (AFI), myocardial performance index (MPI), and foetal Doppler data of the umbilical artery (UA), middle cerebral artery (MCA) and ductus venosus (DV).

RESULTS

The mean gestational age in the controls, the IUGR and any PE cases was 31.4, 31.8 and 31.0 weeks, respectively. The distribution of MPI values was significantly lower in the controls compared to all other groups. The highest standardised MPI values were observed in the PE-IUGR group, where a median of 5.62 was observed. The only significant differences observed between the PE and IUGR groups was the UA resistance index (p = 0.01), where the IUGR cases tended to have higher UA values compared to the combined PE group. Borderline statistical significance was observed for the MCA resistance index values ( p = 0.05) between these groups. The overall adverse event rate in the cases was 49%. The highest rate was observed in the PE + IUGR group, where eight out of 12 (67%) experienced adverse events. MPI z-scores served as a good marker of adverse events, as evidenced by the total area under the curve (AUC) of 0.90 on the ROC curve. A cut-off value of 4.5 on the MPI z-score conferred a sensitivity of 89% and specificity of 68% for an adverse event later in pregnancy. In univariate logistic regression, MPI z-score, AFI, EFW, UA Doppler, CPR category, DV Doppler and MCA Doppler were assessed separately as potential predictors of adverse outcome. The only significant predictor of adverse outcome was MPI z-score.

CONCLUSIONS

A single elevated value of the MPI ( z-score > 4.5) in the third trimester in stable placental-mediated disease was a strong indicator of adverse obstetric outcomes later in pregnancy. This has the potential to be incorporated in conjunction with standard monitoring models in stable placental-mediated disease to predict an adverse event later in pregnancy and thus to reduce perinatal morbidity and mortality.

Cardiac abnormalities in pulmonary oedema associated with hypertensive crises in pregnancy

OBJECTIVE

To describe the cardiac abnormalities by two-dimensional and Doppler echocardiography (echo-Doppler) in hypertensive crises in pregnancy (HCP) complicated by pulmonary oedema and identify pathogenic factors.

DESIGN

A prospective observational study.

SETTING

King Edward VIII Hospital, Durban, South Africa.

PARTICIPANTS

Sixteen patients with HCP complicated by pulmonary oedema over a six-month period. Two control groups, 55 patients with HCP alone and 16 with normotensive pregnancies, were also studied.

RESULTS

Echocardiography diagnosed impaired left ventricular systolic function in 4 of 16 (25%) patients with HCP and pulmonary oedema. In the remaining 12 patients with preserved systolic function, left ventricular diastolic filling abnormalities were demonstrated in a significant proportion compared to control hypertensive and normotensive groups. Fifteen of 16 (94%) study patients presented with pulmonary oedema antepartum; in seven of these patients, the use of dexamethasone to enhance fetal lung maturity appeared to be a contributing factor in precipitating pulmonary oedema.

CONCLUSION

This study demonstrates the value of echo-Doppler to diagnose structural and functional cardiac abnormalities in HCP complicated by pulmonary oedema. The potential role of left ventricular diastolic filling abnormalities in the pathogenesis of pulmonary oedema complicating HCP is discussed.

Continuous electrocardiographic monitoring in hypertensive crises in pregnancy

Twenty-four patients first seen with hypertensive crises during pregnancy were studied by continuous electrocardiographic monitoring for a period of 24 hours to detect the presence of serious ventricular arrhythmias. Three patients were excluded from analysis because of low serum potassium levels. Thirteen of the remaining 21 patients had ventricular tachycardia on subsequent analysis of the electrocardiogram. These arrhythmias subsided after induction of anesthesia when blood pressure control was optimal. This finding may be implicated in the pathogenesis of pulmonary edema and sudden death in these patients.