Pregnancy Labs

Human Chorionic Gonadotropin (hCG)

• Measured in urine or blood
  • blood test more sensitive
• Produced by 
  • syncytiotrophoblast of the placenta after implantation 
• Used to detect pregnancy
• can see pregnancy on transvaginal ultrasound after hCG reaches 1,500-2,000 mIU/mL

Urine Estriol

• Measured in maternal urine
• Produced by
  • fetal adrenal gland
  • maternal liver
  • placenta
• Sign of fetal growth
• ↓ estriol is sign of fetal-maternal-placental dysfunction

α-Fetoprotein (AFP)

• Measured in maternal serum
• ↑ AFP
  • associated with open neural tube defects
• ↓ AFP
• associated with Down syndrome

Lecithin/Sphingomyelin (L:S) Ratio

• Measured in amniotic fluid
  • lecithin is a surfactant produced by fetal lungs
  • used to determine maturity of fetal lungs
• L:S ratio > 2 indicates maturity
• L:S ratio < 2
  • administration of cortisol ↑ lecithin production 
    • fetus normally produces during the stress of vaginal delivery
  • thyroxine also ↑ lethicin production
• insulin ↓ production

First Trimester Screen (10-13 weeks)

• Serum labs
  • serum free β-hCG or total hCG
    • ↑ trisomy 21
    • ↓ trisomy 18 
    • ↓ trisomy 13 
  • pregnancy-associated plasma protein A (PAPP-A)
    • ↓ trisomy 21
    • ↓ trisomy 18 
    • ↓ trisomy 13 
• Imaging
  • nuchal translucency measurement 
    • ↑ trisomy 21
• ↑ trisomy 18 

Quadruple Screen (15-22 weeks)

• Test for aneuploidy  
  • hCG
    • ↑ trisomy 21
    • ↓ trisomy 18
  • alpha fetoprotein (AFP)
    • ↓ trisomy 21
    • ↓ trisomy 18
  • dimeric inhibin A
    • ↑ trisomy 21
    • no change or ↓ trisomy 18
  • unconjugated estriol
    • ↓ trisomy 21
    • ↓ trisomy 18