Initial Blood Work for New Pregnancy
The initial blood work for a new pregnancy should include a complete blood count, blood type and Rh status, screening for infections including HIV, hepatitis B, syphilis, chlamydia, and gonorrhea, as well as rubella immunity status. 1, 2
Core Laboratory Tests for Initial Pregnancy Visit
Essential Blood Tests
Complete Blood Count (CBC) - Screens for anemia, which affects approximately 40% of pregnant women worldwide 3, 4
- Hemoglobin <11.0 g/dL in first trimester indicates anemia
- Mean corpuscular volume (MCV) helps differentiate types of anemia
Blood Type and Rh Status 2
- Critical for identifying Rh-negative women who will need Rh immune globulin at 28 weeks
- Includes ABO blood group and antibody screen
Infectious Disease Screening 2
- HIV testing
- Hepatitis B surface antigen (HBsAg)
- Syphilis serology
- Chlamydia and gonorrhea screening (especially for high-risk populations)
- Hepatitis C antibody testing (for women with risk factors)
Immunity Status
- Rubella antibody testing to determine immunity
Additional First Trimester Tests
- Thyroid-stimulating hormone (TSH) - Consider measuring TSH levels to screen for thyroid dysfunction 1
- Urinalysis - To screen for urinary tract infections and proteinuria 1
Genetic Screening Options
First trimester screening (11-14 weeks) 2
- Nuchal translucency (NT) measurement
- Pregnancy-associated plasma protein A (PAPP-A)
- Human chorionic gonadotropin (hCG) or free beta-hCG
- Detection rate of 75-80% for trisomy cases with 5% false-positive rate
Carrier screening based on family history, ethnicity, and risk factors 2
- Cystic fibrosis and other carrier screening as indicated
Common Pitfalls and Important Considerations
Anemia Detection and Management
- Anemia is the most common hematologic abnormality in pregnancy 3
- Iron deficiency is the most common cause of anemia in pregnancy
- Maternal anemia increases risk of transfusion at delivery and is associated with adverse fetal outcomes
- The 5th percentile for hemoglobin in iron-replete women is approximately 110 g/L in the first trimester 5
Timing of Tests
- Pregnancy dating should be calculated using the first day of the last menstrual period and/or an early-dating ultrasound 2
- First trimester ultrasound (ideally between 7-14 weeks) provides the most accurate dating
- Pregnancy tests can detect hCG as early as 3-4 days after implantation, with 98% accuracy by the time of the expected period 6
Special Considerations
- For women with multiple gestation, more frequent ultrasound examinations are required than for singleton pregnancies 2
- Women with history of preeclampsia should undergo first-trimester screening to assess risk of early-onset preeclampsia 1
- For women at high risk of preterm preeclampsia, aspirin prophylaxis should begin before 16 weeks' gestation 1
By ensuring comprehensive initial blood work, healthcare providers can identify risk factors early and implement appropriate interventions to optimize maternal and fetal outcomes.