SONOGRAPHIC ASSESSMENT IN DIABETIC PREGNANCY

      Meizner I; Greco P

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Antenatal ultrasound plays an important role in monitoring diabetic pregnancies. The ultrasound evaluation should take into consideration the differences between GDM (Gestational Diabetes Mellitus) and PreGDM and therefore, the sonographic approach must be tailored accordingly. The main issues associated with Sonographic assessment of these pregnancies include the following:

1.       Assessment of gestational age

2.       Detection of congenital anomalies

3.       Surveillance of growth 

4.       Dynamic assessment of fetal status (BPS, Doppler)

7.1 Gestational Age Determination:

Evaluation of gestational age is extremely important for accurate monitoring of the advancing pregnancy. Estimation of gestational age should be performed in the first trimester of pregnancy, preferably, using TVS (trans-vaginal sonography). CRL is the best parameter for this purpose. 

7.2 Congenital Anomalies:

With current care, perinatal mortality of the IDDM has been drastically reduced. The main contributor to perinatal mortality and morbidity in these patients is congenital malformations of the fetus.  Abnormalities commonly affecting PreGDM include CNS, Heart, Skeletal, Genitourinary and GIT malformations. The lesion most associated with diabetic embryopathy, the caudal regression syndrome, is actually less common, with an incidence of 1.3 per 1000 diabetic pregnancies. Detection of congenital anomalies should be started in the first trimester of pregnancy and repeated in the second trimester. If possible, early anomaly scan using TVS (transvaginal sonography) may be helpful (14-16 weeks). A basic examination is mandatory in the second trimester of pregnancy and the following organs should be observed: cranium and brain, spine, stomach, bladder, kidneys and insertion of the umbilical cord. The four chamber view of the heart must be obtained; however, a detailed fetal echocardiography performed by a skilled paediatric cardiologist is preferred.

7.3 Fetal Growth Monitoring:

Monitoring fetal growth continues to be a challenging and highly inexact process. Although today’s tools, which involve serial plotting of fetal growth parameters, are superior to earlier clinical estimations, accuracy is still +/- 15%, using the most sophisticated ultrasound equipment. The most important task is to detect fetal macrosomia and IUGR.  Since fetal macrosomia is the most frequent fetal complication of pregnant diabetic patients, a particular effort should be directed toward its diagnosis and management. Thus, unless the patient is not obese and periodic fundal measurements are normal, all pregnant diabetic patients should undergo ultrasound growth assessments of the fetus every several weeks, starting at around 20 weeks of pregnancy for preGDM’s and time of diagnosis for GDM’s. The macrosomic fetus, at some time will be above the 95^th percentile for one or more parameters, most frequently, the abdominal circumference. The positive predictive value for the diagnosis of macrosomia exceeds 90% when the abdominal circumference or the estimated fetal weight is above the 95^th percentile. In IDDM’s, macrosomia is more apparent in some fetal structures: liver, subcutaneous fat, soft tissues of arm, thigh and cheeks. These variables (selective organomegaly) are measurable and may aid in predicting early development of macrosomia.  IUGR is associated with conditions that predispose to uteroplacental insufficiency, and therefore is most likely to appear in DM complicated by severe vasculopathy. In most centres the decision making process regarding time and mode of delivery takes place at around 37-38 weeks of gestation, therefore EFW should be performed at that time.

7.4 Assessment of Fetal Well-Being:

Dynamic assessment of diabetic pregnancies implies two types of investigations: BPS (Biophysical Score) and Doppler studies. The fetal BPS is often applied to evaluate the significance of a nonreactive NST. It may serve as an important tool for fetal surveillance, especially in order to prevent unnecessary early interventions, thereby allowing prolongation of pregnancy beyond 37 weeks. In diabetic gravidas, uteroplacental insufficiency may be difficult to detect by ultrasound assessment of fetal growth, since fetal weight gain can be excessive due to fuel metabolism even when uteroplacental circulation is compromised. Doppler umbilical artery velocimetry has been proposed as a clinical tool for ante-partum fetal surveillance in pregnancies at risk for placental vascular disease. The data is conflicting, and several large studies have now confirmed that ranges for umbilical artery waveforms indices are not different in a diabetic population without pregnancy complications than in the normal controls.

7.5 Proposed Ultrasound Work-Up   in DM Complicating Pregnancy

GDM patients - Ultrasound evaluation should start immediately following diagnosis.

1.       Fetal growth and weight estimations starting at diagnosis and continuing at 3-4 weeks intervals.     

2.       Fetal weight estimation at 37-38 weeks.

3.       BPS at weekly intervals starting at 34 weeks only for insulin treated and/ or patients with poor compliance and control.

PreGDM patients - Ultrasound evaluation should start immediately following diagnosis of pregnancy

1.       8-10 weeks – TVS dating of pregnancy (CRL).

2.       12 weeks – Nuchal translucency (optional).

3.       15 weeks – Transvaginal first detailed anatomical survey of the fetus (optional). Level II evaluation of fetal congenital anomalies is performed at 14–15 weeks and repeated at 20–22 weeks of gestation.

4.       22 weeks – Second detailed anatomical survey of the fetus (abdominal).

5.       20-24 weeks – Fetal echocardiography

6.       Fetal growth and weight estimations starting at 20 weeks, at 3-4 weeks intervals. In all examinations a thorough assessment of all fetal growth parameters is mandatory (BPD, OFD, HC, AC, FL).

7.       Fetal weight estimation at 37-38 weeks

8.       BPS at weekly intervals starting at 32-34 weeks.