Quick answer

NIH lists an adequate vitamin K intake of 90 mcg a day for pregnant women and 75 mcg for teens, and sets no upper limit because no adverse effects have been reported. A systematic review of six older trials found very low quality evidence on newborn bleeding. Ask your doctor first if you take warfarin or another blood thinner.^1,2,3

Key facts

NIH lists adequate intakes of vitamin K in pregnancy of 75 mcg a day for teens and 90 mcg for women aged 19 and older.^1,2
NIH says no upper limit was set because the expert panel found no adverse effects from vitamin K in food or supplements in people or animals. This does not apply to anyone taking warfarin.^1,2
A systematic review of six trials (21,493 mother and newborn pairs) rated its evidence very low quality, and few trials reported side effects in newborns.³
Little vitamin K crosses the placenta, so newborns have little at birth. The American Academy of Pediatrics recommends a single shot at birth.¹
NIH says a sudden change in vitamin K intake can cause dangerous bleeding or blood clots in people taking warfarin.²

What NIH lists for vitamin K in pregnancy

NIH's adequate intake of vitamin K for pregnancy is 75 mcg a day for pregnant teens and 90 mcg for pregnant women aged 19 and older, the same as for other women of those ages. NIH calls these adequate intakes because there was too little data to set a recommended dietary allowance.^1,2

No upper limit has been set for vitamin K, because of its low potential for harm: the expert panel that sets intakes found no reported adverse effects from vitamin K in food or supplements in people or animals. This does not apply to anyone taking warfarin or a similar blood thinner.^1,2

NIH adds that most people in the United States get enough vitamin K from food, that a shortage is very rare in adults, and that bacteria in the large bowel make some forms.^1,2

What a systematic review found about supplements in pregnancy

The main systematic evidence is a review and meta-analysis of vitamin K given to pregnant women. It included six older trials from high-income countries, covering 21,493 mother and newborn pairs, and judged most to be at high or unclear risk of bias. The women were healthy, and the doses, timing and durations varied.³

Newborn bleeding did not differ clearly between groups (risk ratio 1.16, range 0.59 to 2.29), and supplements did raise the mother's blood vitamin K. Few trials reported side effects in newborns, many outcomes were not assessed at all, and the quality of evidence was graded very low for newborn bleeding, newborn jaundice and maternal blood levels. The authors said the findings are uncertain and that more research is needed.³

Newborns and the vitamin K shot

Vitamin K moves poorly across the placenta, which is why newborns start life with low stores. NIH says the American Academy of Pediatrics recommends a single injection of 0.5 to 1 mg of vitamin K1 for every newborn, to prevent a bleeding condition called vitamin K deficiency bleeding. A mother's supplement during pregnancy is a separate question from that shot, and the sources checked do not treat one as a substitute for the other.¹

Little vitamin K crosses the placenta and breast milk is low in it, so newborns have little at birth. The American Academy of Pediatrics recommends a single shot of 0.5 to 1 mg of vitamin K1 for every newborn.¹

Warfarin and pregnancy

NIH's consumer sheet says vitamin K can interact seriously with the blood thinner warfarin, and that anyone taking it should keep the amount of vitamin K from food and supplements about the same every day. A sudden drop can cause dangerous bleeding and a sudden rise can cause blood clots. Anyone who takes warfarin or a related drug and is pregnant or planning a pregnancy should ask their doctor about vitamin K, because changing a supplement or prenatal vitamin alters that balance.^1,2

Who should ask their doctor

A person taking warfarin or a similar anticoagulant, who should ask their doctor before starting, stopping or changing any vitamin K product, including a prenatal vitamin.^1,2
A person on a long course of antibiotics, a bile acid sequestrant or orlistat, which NIH says can lower vitamin K absorption or status.^1,2
A person with a condition that limits fat absorption, such as celiac disease, cystic fibrosis or ulcerative colitis, or who has had weight-loss surgery, since NIH says these people may have trouble getting enough vitamin K.^1,2
Anyone with a bleeding or clotting disorder, who should ask their doctor about all supplements in pregnancy.⁴

Questions people ask

Is vitamin K safe in pregnancy?

NIH sets no upper limit because no adverse effects have been reported from food or supplements, with the warfarin exception. A systematic review of supplements in pregnancy rated its evidence very low quality, so ask your doctor.^1,3

Is vitamin K cream safe during pregnancy?

The sources checked are about vitamin K taken by mouth and say nothing about creams or skin products. That is not a finding either way, so ask your doctor or pharmacist about a cream.¹

Is the vitamin K injection safe during pregnancy?

The injection NIH describes is given to newborns shortly after birth, not during pregnancy. The sources checked do not describe vitamin K injections given to pregnant women, so ask your doctor.¹

Is a vitamin K supplement safe in the first trimester?

The review's summary does not break results down by trimester, and NIH gives one adequate intake for pregnancy. Ask your doctor, especially if you take warfarin or another blood thinner.^1,3

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This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.