The gestational diabetic cases from four case-control studies [6, 7, 8, 9] by our research group were combined to form a total sample of 159 cases for validation of the risk scoring system. The recruitment, categorization of degree of gestational diabetes, methodology in performing the myocardial performance index and management of patients were consistent and standard across the studies and could be combined to form a total sample for validation of the risk scoring system. All studies were prospective cross sectional studies of the MPI in fetuses of gestational diabetic pregnancies conducted at the tertiary referral Fetal Unit at Inkosi Albert Luthuli Central Hospital in Durban, South Africa. All patients were in the 3rd trimester of pregnancy.
The cases included poorly or suboptimally controlled gestational diabetics, well controlled gestational diabetics and gestationally impaired glucose tolerance patients. All patients in the study groups were categorized by a combination of an oral glucose tolerance test, blood glucose profiles and measurement of glycosylated haemoglobin levels (HbA1C%) within 4 weeks of the echocardiographic assessment.
Poor or suboptimal control was defined by suboptimal blood glucose profiles and measurement of glycosylated haemoglobin level (HbA1C%) within 4 weeks of the echocardiographic assessment revealing poor or suboptimal blood glucose control of the study patients with an average HbA1C of 64 mmol/mol [ 8%] or more (National Institute for Health and Care Excellence NICE guidelines for gestational diabetes [Clinical Guideline 63] state that women with diabetes should aim to achieve an HbA1C level of 43.3mmol/mol [6.1%] or lower). Two studies were performed in this category of gestational diabetics; in the first study 29 consecutive poorly controlled gestational diabetic women on insulin in the 3rd trimester were recruited matched with 29 normal controls[6] and in the 2nd study 44 consecutive poorly controlled women on insulin were recruited in the 3rd trimester matched with 44 controls[7].
Well controlled gestational diabetics were defined firstly by the WHO ‘s criteria of a 2hr level > 7.8mmol/l and < 11.0mmol/l after 75g oral glucose tolerance test (OGTT) in the 3rd trimester [11] and on review of self monitoring blood glucose levels achieving 2 hr post-prandial levels of < 7mmol/l and pre-prandial levels < 5.5mmol/l. All patients in the well-controlled gestational diabetic group had HbA1c results of < 6% reflecting good control. The well- controlled group achieved good control on medication either metformin or insulin. 54 consecutive well controlled women were recruited in the 3rd trimester with matched controls.
GIGT patients were defined firstly by the WHO ‘s criteria of a 2hr level > 7.8mmol/l and < 11.0mmol/l after 75g oral glucose tolerance test (OGTT) in the 3rd trimester[11] and on review of self monitoring blood glucose levels achieving 2 hr post-prandial levels of < 7mmol/l and pre-prandial levels < 5.5mmol/l. All patients in the GIGT group had HbA1c results of < 6% reflecting good control. In this group control was achieved only on diet. Thirty-two consecutive women defined as GIGT were recruited in the 3rd trimester with matched controls.
The mean gestational age at which MPI was performed in all studies was between 33–35 weeks gestation. All studies were prospective and cross-sectional.
All the different gestational diabetic categories had control groups that were randomly selected from the antenatal clinic and who were not diabetic as defined by the WHO criteria of a 2hr level < 7.8mmol after a 75g OGTT[11]. The controls were matched for gestational age, maternal age, parity, gravidity, BMI and past obstetric history at inclusion in all the patients.
All pregnancies in all studies in both the study and control groups were spontaneously conceived.
Pregestational diabetics according to history were excluded from recruitment to exclude possible microvascular complications which could be a confounding variable and to give conformity to the study groups. Exclusion criteria in all studies were multiple pregnancies, congenital malformations, evidence of placental mediated disease and abnormal fetal heart rates (either tachycardia or bradycardia). Placental mediated disease was defined by either the presence of growth restriction (AC < 10th percentile for gestational age with an elevated umbilical artery resistance index > 90th percentile for gestational age) and/or presence of pre-eclampsia as defined by a blood pressure of greater than 140/90mmHg with proteinurea[12].
Ethical approval for all studies was obtained from the Biomedical Research Ethics Committee at the University of Kwa-Zulu Natal. All studies were performed in accordance with the Declaration of Helsinki. All participants were adult over 18 years. All participants provided written informed consent to participate in this study.
Fetal echocardiography using either an E8 General Electric Voluson Ultrasound system (GE Medical Systems WI, USA) or Siemens Antares ultrasound system (Siemens Medical Systems Malvern PA, USA) was performed in each woman in all studies. The four chamber view,outflow tract views, triple vessel view, longitudinal view of the aortic arch and colour flow mapping were used to screen for cardiac malformations.
The MPI in all studies was calculated in the fetal left ventricle[10, 13]. Our previous study established reference intervals and trends of the MPI in normal pregnancies and the methodology of obtaining the MPI has been described in detail in the paper[10]. A cross sectional image of the fetal thorax at the level of the 4-chamber view with an apical projection of the heart was obtained. The Doppler sample was opened to 3mm and placed in the internal leaflet of the mitral valve (MV). In this location owing to its closeness to the aortic valve (AV), the opening and closing AV clicks were registered. The angle of insonation was always < 30 degrees. E/A waveform was always displayed as positive flow. The Doppler gain was lowered as far as possible to clearly visualize the echoes corresponding to the opening and closing clicks of the two valves at the beginning and at the end of the mitral valve and aortic waveforms. The peak of the valve clicks was used in the measurement of the time intervals rather than the base, as it is a clearer landmark, overcoming variations in valve click width and resulting in better reproducibility [10, 14, 15]. The Doppler sweep velocity was set at 5cm/sec and wall motion filter at 300Hz. The three time periods were estimated as follows :Isovolumetric contraction time (ICT) from beginning of MV closure to AV opening; Ejection time (ET) from AV opening to closure;Isovolumetric relaxation time (IRT) from AV closure to MV opening.The Mod-MPI = (ICT + IRT) /ET. We have previously documented high levels of inter- and intraobserver variability agreement for the MPI and its components in our paper establishing reference intervals of mod-MPI in normal pregnancies [10].
In addition to the echocardiographic data, sonographic data including estimated fetal weights and amniotic fluid indices were determined and recorded. The umbilical artery (UA) resistance (RI) and pulsatility index (PI), middle cerebral artery (MCA) pulsatility index (PI) and ductus venosus pulsatility index (PI) were also determined in both groups. Cerebroplacental ratio was then determined.
All patients in all studies were delivered according to existing standard protocols for diabetic pregnant patients at our institution, which includes non-reassuring fetal cardiotocogram (CTG) findings, poor biophysical profiles, or persistent elevations of UA RI/PI. If fetal monitoring was satisfactory, delivery was delayed until 39–40 weeks after which the patient would be induced or caesarean section performed for obstetrical reasons.
Pregnancy outcomes were recorded in both groups. An abnormal outcome in our studies was defined as any one of the following: stillbirth, neonatal death, tachypnoea with pulmonary oedema, neonatal hypoglycaemia, neonatal cord pH < 7.2, 5 min Apgar score < 7, polycythaemia and nucleated red blood cells > 10/100 white blood cell counts (markers for hypoxia), cardiomyopathy, NICU admissions.
Cardiac Doppler data were not used by clinicians in the management of the diabetic patients.
For details of methodology of each study please refer to the individual published studies [6, 7, 8, 9].
Statistical Analysis
Univariate logistic regression was used to assess the effect of individual risk factors with proposed cutoffs on adverse pregnancy outcome. The diagnostic accuracy of the total summative score, was assessed by computing the area under the ROC curve and by examining the sensitivity and specificity at key cutpoints of interest.