From the Guidelines
At a 24-week prenatal visit, a glucose challenge test (50g glucose load with blood draw at 1 hour) should be conducted to screen for gestational diabetes, as this condition typically develops in the second trimester and can affect both maternal and fetal health. This recommendation is based on the most recent and highest quality study, which suggests that screening for gestational diabetes mellitus (GDM) at 24-28 weeks of gestation is essential for identifying women at risk of adverse pregnancy and neonatal outcomes 1.
Recommended Laboratory Tests and Diagnostic Procedures
The following tests and procedures are recommended at 24 weeks gestation:
- Glucose challenge test (50g glucose load with blood draw at 1 hour) to screen for gestational diabetes
- Blood pressure measurement and urine protein screening to monitor for preeclampsia
- Fundal height measurement to assess fetal growth
- Fetal heart rate monitoring to confirm fetal well-being
- Complete blood count (if not already done) to check for anemia
- Administration of Rh immunoglobulin (RhoGAM) at 28 weeks for Rh-negative mothers to prevent Rh sensitization
Additional Recommendations
It is also recommended to discuss and schedule the third-trimester ultrasound (typically at 32-36 weeks) to assess fetal growth, placental position, and amniotic fluid levels. Patients should be educated about monitoring fetal movement patterns and recognizing signs of preterm labor, as the risk increases after 24 weeks. The diagnosis of GDM can be made using either the one-step or two-step protocol, depending on regional preferences, with the one-step strategy involving a 75-g oral glucose tolerance test (OGTT) and the two-step strategy involving a 50-g glucose load test (GLT) followed by a 100-g OGTT if the initial test is abnormal 1.
Importance of Early Detection and Treatment
Early detection and treatment of GDM are crucial to reduce the risk of adverse pregnancy and neonatal outcomes, such as large-for-gestational-age births and preeclampsia. The American Diabetes Association (ADA) recommends that all pregnant women not known to have prior diabetes undergo a 75-g OGTT at 24-28 weeks of gestation based on an International Association of Diabetes and Pregnancy Study Groups (IADPSG) consensus meeting 1.
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From the Research
Laboratory Tests at 24 Weeks Gestation
- At 24 weeks gestation, the following laboratory tests and diagnostic procedures are recommended:
- The 75g-OGTT is recommended for the diagnosis of GDM between 24-28 weeks of pregnancy, as it provides a faster diagnosis time, better tolerance, and is easier to remember 2
- Fasting blood glucose should be measured at the first visit during early pregnancy for patients with risk factors, but oral glucose tolerance testing during early pregnancy is not currently recommended for the detection of GDM 4
Diagnostic Procedures
- Non-invasive fetal RhD prediction may be offered to RhD-negative pregnant women at gestational age of 25 weeks 5
- Serial monitoring of titer and specificity of alloantibodies may be initiated if an alloantibody is detected in the first trimester screen 5
- Umbilical artery, middle cerebral artery, and ductus venosus Doppler flow may be used to assess fetal wellbeing, particularly in high-risk pregnancies 6
Anemia Screening
- The American College of Obstetricians and Gynecologists recommends screening for anemia with a complete blood count in the first trimester and again at 24 0/7 to 28 6/7 weeks of gestation 3
- Mild anemia with a hemoglobin of 10.0 g/dL or higher and a mildly low or normal mean corpuscular volume (MCV) is likely iron deficiency anemia, and a trial of oral iron can be both diagnostic and therapeutic 3