From the Guidelines
All pregnant women should undergo laboratory tests for undiagnosed prediabetes and diabetes at the first prenatal visit if they have risk factors, and all pregnant women not previously known to have diabetes should be evaluated for gestational diabetes mellitus (GDM) at 24 to 28 weeks of gestation.
Indications for Laboratory Tests in Pregnancy
- Risk factors for diabetes: Test for undiagnosed prediabetes and diabetes at the first prenatal visit using standard diagnostic criteria 1.
- Gestational Diabetes Mellitus (GDM): Evaluate all pregnant women not previously known to have diabetes for GDM at 24 to 28 weeks of gestation 1.
- Postpartum screening: Test women with GDM for prediabetes or diabetes at 4–12 weeks postpartum, using the 75-g oral glucose tolerance test and clinically appropriate non-pregnancy diagnostic criteria 1.
- Lifelong screening: Women with a history of GDM should have lifelong screening for the development of diabetes or prediabetes at least every 3 years 1.
Laboratory Tests
- Fasting glucose: Use fasting glucose of 110–125 mg/dL (6.1 mmol/L) or A1C 5.9–6.4% (41–47 mmol/mol) to screen for early abnormal glucose metabolism 1.
- 75-g oral glucose tolerance test: Use this test to screen for GDM and to test women with GDM for prediabetes or diabetes at 4–12 weeks postpartum 1.
From the Research
Laboratory Tests for New Pregnancy
The following laboratory tests are indicated for a new pregnancy:
- Maternal prenatal screening and serologies, which include measuring antigen or antibody titers, a combination of antigen/antibody titers, or by specialized genetic tests 2
- Pregnancy tests, which depend on the measurement of human chorionic gonadotrophin (HCG) in urine 3, 4
- Routine laboratory tests, such as blood tests for systemic blood, coagulation parameters, total protein and protein fractions, non-protein nitrogen blood components, glucose, electrolytes, indicating enzymes and excretory enzymes of protein metabolism, lipid fractions 5
- Clinical chemistry tests, including plasma alanine aminotransferase, albumin, alkaline phosphatase, pancreas amylase, apolipoprotein A1, apolipoprotein B, aspartate aminotransferase, bilirubin, calcium, chloride, creatinine, cystatin C, ferritin, gamma-glutamyltransferase, iron, lactate dehydrogenase, magnesium, phosphate, potassium, sodium, transferrin, triglycerides, thyroid-stimulating hormone, urate and urea 6
Timing of Laboratory Tests
These laboratory tests should be performed at the first provider visit once pregnancy has been confirmed, with additional screenings varying based on the specific disease and on maternal risk factors 2 The tests can be performed at different stages of pregnancy, including:
- Gestational week 7-17
- Week 17-24
- Week 24-28
- Week 28-31
- Week 31-34
- Week 34-38
- Predelivery (0-2 weeks before delivery)
- Postpartum (> 6 weeks after delivery) 6
Importance of Laboratory Tests
Laboratory tests are essential in preventing pregnancy complications and predicting neonatal and infant medical issues after delivery 2 The tests can help identify diseases and conditions that may affect the mother and the fetus, and guide clinical decisions and management 2, 5, 6