What laboratory tests should be ordered at the initial prenatal visit in the first trimester?

Initial Prenatal Laboratory Testing

All pregnant women should undergo comprehensive laboratory screening at the first prenatal visit, including complete blood count, blood type and antibody screen, rubella immunity, syphilis serology, hepatitis B surface antigen, HIV testing, urinalysis, and cervical cultures for gonorrhea and chlamydia, with additional glucose screening for high-risk women. 1

Essential First Trimester Laboratory Tests

Hematologic Assessment

• Complete blood count (CBC) to screen for anemia and establish baseline hemoglobin levels 2, 1
• Blood type (ABO) and Rh status to identify women requiring Rh immunoglobulin prophylaxis 1, 3
• Antibody screen to detect irregular antibodies that could cause hemolytic disease of the fetus and newborn 1, 4

Infectious Disease Screening

• Hepatitis B surface antigen (HBsAg) to identify carriers and prevent vertical transmission 2, 1
• HIV antibody testing should be offered to all pregnant women 2, 1
• Syphilis serology (RPR or VDRL) to detect and treat maternal syphilis 2, 1
• Rubella antibody status to identify non-immune women who need postpartum vaccination 2, 1
• Gonorrhea and chlamydia screening via cervical cultures at the initial visit 2, 1

Metabolic Screening

• Fasting blood glucose at the first prenatal visit to screen for pre-existing diabetes 1
• Immediate glucose testing for women with marked obesity, prior gestational diabetes, strong family history of diabetes, or other high-risk characteristics 1
• Women with negative early testing but persistent risk factors should be retested at 24-28 weeks 1

Renal Assessment

• Urinalysis to screen for asymptomatic bacteriuria, proteinuria, and glucosuria 2
• Serum creatinine and urinary albumin-to-creatinine ratio in women with chronic hypertension or pre-existing diabetes 1

Cervical Screening

• Cervical cytology (Pap smear) should be obtained at the initial visit according to standard screening guidelines 1

First Trimester Aneuploidy Screening (11-14 Weeks)

Combined First Trimester Screening

• Nuchal translucency (NT) measurement via ultrasound between 11 weeks 4 days and 13 weeks 6 days 2, 3
• Pregnancy-associated plasma protein A (PAPP-A) - typically reduced in Down syndrome 2
• Human chorionic gonadotropin (hCG or free beta-hCG) - elevated in Down syndrome 2
• This combined approach achieves approximately 85-92% detection rate for Down syndrome with 1-5% false-positive rate 2, 3

Important caveat: NT measurement requires sonographers with specific training and certification through quality assurance programs 2

Additional Testing for High-Risk Women

Women with Chronic Hypertension

• Liver enzymes and function tests to establish baseline 1
• Uric acid levels as elevated levels predict worse maternal and fetal outcomes 1
• Complete metabolic panel to detect superimposed preeclampsia, which complicates up to 25% of pregnancies with chronic hypertension 1

Women with Pre-existing Diabetes

• Hemoglobin A1C to assess glycemic control 1
• Thyroid-stimulating hormone (TSH) 1
• Serum creatinine and urinary albumin-to-creatinine ratio 1

Second Trimester Testing (Not Initial Visit, But Part of Comprehensive Prenatal Care)

Gestational Diabetes Screening

• 50-gram glucose challenge test or oral glucose tolerance test at 24-28 weeks for average-risk women 1

Neural Tube Defect Screening

• Maternal serum alpha-fetoprotein (MSAFP) between 16-18 weeks for women who had first trimester screening or CVS 2, 1

Common Pitfalls to Avoid

• Failing to screen for hepatitis B in the first trimester - this is crucial for preventing mother-to-child transmission through timely intervention 1
• Delaying glucose screening in high-risk women - testing should occur at the first prenatal visit, not waiting until 24-28 weeks 1
• Not obtaining blood type and antibody screen - missing this can result in failure to provide Rh immunoglobulin prophylaxis to appropriate candidates 1, 3
• Inadequate follow-up of positive antibody screens - women with irregular antibodies require serial titer monitoring and fetal surveillance 4
• Performing NT measurements outside the 11+4 to 13+6 week window - measurements outside this range are not valid for aneuploidy screening 2, 3