What blood tests are recommended during the first trimester of pregnancy?

Recommended Blood Tests for First Trimester of Pregnancy

All pregnant women should undergo comprehensive blood work screening in the first trimester, including complete blood count, blood typing, hepatitis B surface antigen, blood glucose screening, and infectious disease testing to identify potential complications early and ensure optimal maternal and fetal outcomes. 1

Essential First Trimester Laboratory Tests

• Complete blood count (CBC) to assess for anemia and other hematologic abnormalities 1
• Blood typing and antibody screening to identify potential blood incompatibilities and determine Rh status 1, 2
• Hepatitis B surface antigen (HBsAg) screening to recognize and reduce the risk of HBV mother-to-child transmission 1, 3
• HIV testing for early identification and management to prevent vertical transmission 1, 4
• Rubella immunity to identify susceptible women who will need vaccination postpartum 1, 4
• Syphilis screening to detect and treat infection early 1, 4
• Serum beta-human chorionic gonadotropin (β-hCG) as needed for pregnancy confirmation or monitoring 3, 5

Additional Recommended First Trimester Tests

• Fasting blood glucose to screen for pre-existing diabetes 1, 3
• Thyroid-stimulating hormone (TSH) testing, particularly important for women with pre-existing diabetes or thyroid disorders 1, 3
• Cytomegalovirus and toxoplasmosis serology in regions where screening is recommended 4
• Hepatitis C virus (HCV) screening, especially for women with risk factors 1, 4
• Cervical cultures and Pap smear should be obtained at the initial visit 1

Aneuploidy Screening Options

• First trimester screening (11-14 weeks) includes:
  • Nuchal translucency (NT) measurement via ultrasound 6
  • Pregnancy-associated plasma protein A (PAPP-A) 6
  • Human chorionic gonadotropin (hCG) or free beta-hCG 6
• Women should be informed that first trimester screening has a detection rate of approximately 70% for Down syndrome with a 5% false-positive rate 6
• All women should have the option of invasive diagnostic testing (CVS or amniocentesis) regardless of maternal age 6

Special Considerations

• For RhD-negative women: Additional antibody screening and potentially non-invasive fetal RhD prediction later in pregnancy 7, 2
• For women with chronic hypertension: More comprehensive baseline laboratory assessment including liver enzymes, renal function, and uric acid levels 1
• For women with pre-existing diabetes: Additional testing including A1C, comprehensive eye examination, and urinary albumin-to-creatinine ratio 1
• For multiple gestations: Standard first trimester screening, though combined ultrasound and serum screening may be less sensitive than in singleton pregnancies 6

Common Pitfalls to Avoid

• Failing to screen for hepatitis B in the first trimester, which is crucial for preventing mother-to-child transmission 1
• Delaying glucose screening in high-risk women, which should be performed as early as possible in pregnancy 1
• Not providing adequate counseling regarding screening options for aneuploidy and the benefits, risks, and limitations of different tests 6
• Overlooking the importance of baseline laboratory tests in women with chronic medical conditions 1
• Not following up on abnormal results promptly or failing to reinterpret test results if gestational age is revised 6

Second Trimester Follow-up Testing

• Maternal serum alpha-fetoprotein (MSAFP) screening for detection of open neural tube defects and anencephaly should be offered between 16-18 weeks gestation, even to women who had first trimester screening 6
• Multiple marker screening (AFP, hCG, uE3 with or without INH-A) should be offered to women who did not have first trimester screening 6, 3
• Glucose challenge test for gestational diabetes screening at 24-28 weeks for average-risk women 1, 3