What laboratory tests and medications are recommended for pregnant individuals in their first trimester?

First Trimester Laboratory Tests and Medications for Pregnant Individuals

The essential first trimester laboratory tests include complete blood count, blood type and Rh status, infection screenings (HIV, hepatitis B, syphilis, chlamydia, gonorrhea), rubella immunity status, thyroid function testing, and urinalysis, while all pregnant women should take folic acid supplementation (0.4-0.8 mg daily) with higher doses (4-5 mg) for high-risk women. 1

Essential Laboratory Tests

Basic Screening

• Complete blood count (CBC)
• Blood type and Rh status
• Urinalysis for urinary tract infections and proteinuria 1

Infection Screening

• HIV testing
• Hepatitis B surface antigen (HBsAg)
• Syphilis serology
• Chlamydia and gonorrhea screening (especially for high-risk populations)
• Rubella immunity status 1

Metabolic and Endocrine Testing

• Thyroid-stimulating hormone (TSH) to screen for thyroid dysfunction 1
• Consider hepatitis C antibody testing for women with risk factors (history of injection drug use or transfusion/organ transplant before 1992) 1

Genetic and Fetal Screening

• First trimester screening (11-14 weeks) includes:

  • Nuchal translucency (NT) measurement
  • Pregnancy-associated plasma protein A (PAPP-A)
  • Human chorionic gonadotropin (hCG) or free beta-hCG 2, 1

• This combined screening has a detection rate of 75-80% for trisomy cases with a 5% false-positive rate 1

• For definitive diagnosis of fetal aneuploidy:

  • Chorionic villus sampling (CVS) from 10-13 weeks
  • Amniocentesis after 15 weeks 2, 1

Recommended Medications

Folic Acid

• Standard dosage: 0.4 mg daily for adults and children 4 or more years of age
• Pregnant and lactating women: 0.8 mg daily 3
• Higher doses (up to 4-5 mg) may be prescribed for women at increased risk of neural tube defects, but doses above 1 mg do not enhance the hematologic effect 3, 4
• High-dose supplementation (4-5 mg) increases maternal serum folate but not red blood cell folate concentrations, suggesting tissue saturation 4

Aspirin Prophylaxis

• For women at high risk of preterm preeclampsia, aspirin prophylaxis should be initiated before 16 weeks' gestation at a dose of 150 mg to be taken every night until 36 weeks' gestation 2, 1

Calcium Supplementation

• For women with low calcium intake (<800 mg/day), calcium supplementation (1.5-2 g elemental calcium/day) may reduce the risk of preeclampsia 2

Special Considerations

Preeclampsia Risk Assessment

• Women with a history of preeclampsia should undergo first-trimester screening to assess the risk of early-onset preeclampsia 2, 1
• HELLP syndrome (Hemolysis, Elevated Liver enzymes, Low Platelets) should be considered a manifestation of severe preeclampsia 2

Hepatitis Management

• Screening for HBsAg in the first trimester is recommended to reduce the risk of HBV mother-to-child transmission 2
• Women with HCV infection should be counseled to undergo antiviral treatment before pregnancy or after delivery and breastfeeding 2
• Women on tenofovir treatment for hepatitis B should continue treatment during pregnancy 2

Multiple Gestation

• Multiple gestation assessment requires establishing chorionicity and amnionicity
• Twin pregnancies require more frequent ultrasound examinations than singleton pregnancies 1

Imaging During First Trimester

• First trimester ultrasound (ideally between 7-14 weeks) provides the most accurate pregnancy dating, with a standard deviation of ±7 days 1
• Crown-rump length measurement between 7-14 weeks provides an accuracy of ±7 days 1
• Ultrasound without contrast is the preferred imaging modality throughout pregnancy 1

Common Pitfalls to Avoid

• Folic acid in doses above 0.1 mg daily may obscure pernicious anemia by alleviating hematologic manifestations while allowing neurologic complications to progress 3
• Folic acid may antagonize the anticonvulsant action of phenytoin, potentially requiring increased doses of phenytoin to prevent convulsions 3
• False low serum and red cell folate levels may occur if the patient has been taking antibiotics such as tetracycline 3
• Avoid using predetermined cutoffs based on age risk for screening programs, as age is no longer used as a cutoff to offer invasive testing 2

By following these comprehensive first trimester laboratory testing and medication guidelines, healthcare providers can optimize maternal and fetal outcomes through early detection and management of potential complications.