Vitamin K supplementation has not been shown to have any benefit during pregnancy in women who are not deficient, and all vitamin K required during pregnancy can be obtained through a varied diet.
Further, supplementation of vitamin K to pregnant women does not appear to have any effect on the vitamin K status of their newborns (but deficiency can make it worse).
Supplementation is only recommended if pregnant women are taking anticoagulant or epileptic medication, have taken certain antibiotics for an extended period of time, have a poor diet, or have a bleeding disorder. Women should not start or stop any medication/supplementation without speaking to their health care provider (HCP).
Background
Vitamin K is a fat-soluble vitamin; its most well-known role in the human body is its role in blood clotting ("K" is derived from the German word "koagulation" meaning to clot blood or prevent hemorrhage). Anticoagulant proteins dependent on vitamin K are found in the kidney, brain, liver, heart, pancreas, and bone.
Vitamin K status is traditionally assessed by blood clotting time (if blood takes longer to clot, the individual is assessed to be deficient).
Some anticoagulants used to prevent blood clots essentially block vitamin K activity as their mechanism of action. Individuals taking some anticoagulants need to monitor their vitamin K status to avoid extreme deficiency and risk of heavy, excessive bleeding; sudden changes in vitamin K can increase or decrease the anticoagulant effect of these medications.
Women should never take vitamin K supplements without talking to their HCP.
Pregnancy
The specific importance of vitamin K during pregnancy is not understood, but data suggests there is no additional requirement or need to supplement with vitamin K during pregnancy.
Further, vitamin K supplementation while pregnant is not recommended solely to avoid vitamin K deficiency in the newborn, as this has only been shown to assist the mother.
Vitamin K levels (and related clotting factors) are naturally low in the fetus and newborn due to the very slow transfer rate through the placenta.
Vitamin K deficiency bleeding is a bleeding disorder in newborns that can lead to hemorrhaging inside the baby’s skull soon after birth, and newborns are routinely given vitamin K after birth. Newborns of mothers who had a vitamin K deficiency during pregnancy may be at an even higher risk of hemorrhaging.
Current studies have not shown any benefit of vitamin K supplementation in the mother on the reduction of neonatal bleeding, but it did improve the mother’s vitamin K status.
Deficiency
Fortunately, deficiency in pregnant women (and adults in general) is very rare; vitamin K is widespread in foods and the vitamin has its own “recycle” ability within the body to conserve and reuse itself when necessary.
Bleeding and hemorrhage are the classic signs of vitamin K deficiency, which are serious and sometimes fatal during pregnancy. Other deficiency symptoms include easy bruising, nosebleeds, bleeding gums, blood in the urine, or blood in the stool (a tarry black color).
Supplementation
Vitamin K is present in most multivitamins, typically less than 75% of the daily value.
Most diets in the United States are assessed to contain an adequate amount of vitamin K, but – in general – the requirement for vitamin K is difficult to estimate.
The adequate intake for vitamin K has been proposed to be 90 mcg/day (300 IU) during pregnancy, although it has been speculated that even levels up to 120 mcg (400 IU) may not be sufficient.
Pregnant women who take anticonvulsant drugs are advised to have vitamin K supplementation either 2 or 4 weeks before delivery and be monitored closely.
Pregnant women taking certain antibiotics or those with Crohn’s disease, cystic fibrosis, celiac disease, or any other malabsorption conditions may also need vitamin K supplementation at the recommendation of their HCP. Note: Absorption of vitamin K may be more efficient within a multivitamin as opposed to its own separate tablet/pill.
Vitamin K supplements are usually only needed for antibiotic use if the antibiotic has been taken for an extended time and vitamin K dietary intake is poor.
It appears that excessive vitamin K supplementation has no adverse effects during pregnancy, but evidence quality is considered low. It is possible neonatal bleeding or jaundice could occur, but data is limited.
Food Sources
Vitamin K is contained in a variety of foods, such as dairy products, meat, eggs, spinach, broccoli, iceberg lettuce, fats and oils, kale, pumpkin, chicken, edamame, and pomegranate (breakfast cereals and breads are generally not fortified with Vitamin K).
Contrary to other nutrients, little vitamin K is lost from foods with ordinary cooking, and therefore all vitamin K needed can be obtained through a varied diet.
Action
Pregnant women taking certain antibiotics, anticoagulant medications, or those with Crohn’s disease, cystic fibrosis, celiac disease, or any other malabsorption conditions should discuss their vitamin K status with their HCP.
Women should not start or stop any medication/supplementation (to include vitamin K) without speaking to their HCP.
Women should also consider having an overall discussion with their provider regarding nutrition, as well as an assessment of their current diet. HCPs are trained to look for areas in which women may be able to improve their nutrition during pregnancy based on vitamins/minerals they may be lacking.
Resources
Vitamin K Fact Sheet (U.S. National Institutes of Health)