What is vitamin K's role in pregnancy?

Vitamin K's Role in Pregnancy

Vitamin K plays a critical role in pregnancy by supporting fetal coagulation factor development and preventing potentially fatal hemorrhagic complications in newborns. 1, 2

Importance of Vitamin K During Pregnancy

Vitamin K is essential during pregnancy for several key reasons:

• Fetal coagulation development: The fetal liver requires vitamin K to produce functional coagulation factors (II, VII, IX, X)
• Prevention of hemorrhagic disease: Without adequate vitamin K, newborns face significantly elevated bleeding risks
• Risk management: The risk of vitamin K deficiency bleeding (VKDB) in newborns is approximately 1/59 (1700/100,000) without prophylaxis 3

Maternal Vitamin K Status and Fetal Impact

Maternal vitamin K status directly impacts the fetus because:

• Vitamin K antagonists (like warfarin) cross the placenta and can cause:

  • Fetal hemorrhagic complications
  • Increased risk of pregnancy loss 1
  • Potential embryopathy when used in early pregnancy
  • CNS abnormalities with exposure during any trimester 1

• The fetal liver is immature with naturally low levels of vitamin K-dependent coagulation factors, making vitamin K status particularly important 1

Management Considerations for Pregnant Women on Vitamin K Antagonists

For women on vitamin K antagonist therapy who are planning pregnancy:

1. Pre-conception counseling is essential regarding risks 1

2. Medication substitution options:

   • Replace vitamin K antagonists with LMWH or UFH before conception
   • Perform frequent pregnancy tests and substitute LMWH/UFH when pregnancy is achieved 1

3. Delivery planning:

   • Substitute UFH or LMWH for vitamin K antagonists approximately 3 weeks prior to delivery
   • Discontinue these medications shortly before delivery 1

Newborn Vitamin K Prophylaxis

Vitamin K prophylaxis is critical for all newborns, especially those born to mothers on vitamin K antagonists:

• Standard recommendation: The American Academy of Pediatrics recommends a single intramuscular dose of phytonadione 0.5 to 1 mg within one hour of birth 4
• Efficacy: This reduces VKDB risk from 1/59 to 1/100,000 3
• Special cases: For infants born to mothers on warfarin, immediate vitamin K administration at birth is required with close monitoring for delayed bleeding complications 2

Alternative Anticoagulants During Pregnancy

When anticoagulation is needed during pregnancy:

• UFH and LMWH are preferred as they do not cross the placenta and are safe for the fetus 1
• Fondaparinux has limited data in pregnancy and should be used with caution 1
• Direct thrombin inhibitors have insufficient safety data for pregnancy use 1

Monitoring and Follow-up

For pregnant women on anticoagulants and their newborns:

• Monitor INR within 24-48 hours after initiating treatment 2
• For significant elevations, consider vitamin K administration 2
• For newborns, check for signs of vitamin K deficiency including:
  • Prolonged prothrombin time
  • Normal fibrinogen level and platelet count 5

Common Pitfalls and Caveats

• Terminology: The historical term "hemorrhagic disease of the newborn" is outdated; "vitamin K deficiency bleeding" (VKDB) is preferred 5
• Oral vs. intramuscular prophylaxis: While oral vitamin K can prevent classic VKDB, parenteral administration appears more effective for preventing late VKDB, especially in infants with hepatobiliary disease 5
• Maternal supplementation: Vitamin K supplementation during pregnancy has not been conclusively shown to prevent VKDB in newborns 6
• Breastfeeding: Breast milk contains very low levels of vitamin K compared to formula, making breastfed infants at higher risk for VKDB without prophylaxis 7