Vitamin K is a fat-soluble vitamin essential for blood clotting and bone health during pregnancy. Whilst frank deficiency is uncommon in the UK, understanding vitamin K's role helps expectant mothers make informed dietary choices. This vitamin supports maternal clotting factor synthesis and contributes to fetal skeletal development, though placental transfer remains limited. Most pregnant women obtain adequate vitamin K through a balanced diet rich in green leafy vegetables. However, certain medical conditions and medications—particularly anticonvulsants and malabsorption disorders—may increase deficiency risk. This article explores vitamin K requirements, dietary sources, potential risks, and when specialist input may be needed during pregnancy.

Why Vitamin K Matters During Pregnancy

Vitamin K is a fat-soluble vitamin essential for blood clotting and bone metabolism, playing a crucial role throughout pregnancy for both maternal and fetal health. This vitamin exists in two primary forms: vitamin K1 (phylloquinone), found predominantly in green leafy vegetables, and vitamin K2 (menaquinone), which can be produced by intestinal bacteria and is present in fermented foods and animal products. During pregnancy, vitamin K serves as a cofactor for the synthesis of clotting factors II, VII, IX, and X, which contribute to normal blood clotting processes.

The developing fetus has limited vitamin K stores, and while some transfer occurs across the placenta, this appears to be relatively modest. This physiological limitation means that newborns are born with naturally low vitamin K levels, which is why vitamin K prophylaxis is routinely offered for all newborns in the UK, regardless of maternal diet or status. Additionally, vitamin K contributes to the activation of proteins involved in bone mineralisation, supporting skeletal development in the growing baby.

Whilst frank vitamin K deficiency is uncommon in healthy pregnant women in the UK, certain medical conditions and medications can interfere with vitamin K metabolism. Pregnant women taking anticonvulsants (such as phenytoin or carbamazepine) or those with malabsorption disorders (including coeliac disease or inflammatory bowel disease) may be at increased risk. Understanding the importance of vitamin K helps expectant mothers make informed dietary choices and recognise when additional monitoring might be necessary. The NHS emphasises a balanced diet during pregnancy, which naturally provides adequate vitamin K for most women without requiring specific supplementation.

Vitamin K Requirements and Dietary Sources in Pregnancy

The UK does not have a specific recommended nutrient intake for vitamin K during pregnancy, as requirements are not thought to increase significantly above the general adult recommendation. The Department of Health advises a safe intake of approximately 1 microgram per kilogram of body weight daily for adults, which translates to roughly 60–70 micrograms for most women. Fortunately, this requirement is readily achievable through a varied, balanced diet without the need for routine supplementation.

Excellent dietary sources of vitamin K1 include dark green leafy vegetables such as kale, spinach, spring greens, broccoli, and Brussels sprouts. A single 80-gram portion of cooked kale can provide approximately 400 micrograms of vitamin K, far exceeding daily requirements. Other good sources include vegetable oils (particularly rapeseed and soya oil), green beans, peas, and herbs like parsley and coriander. Vitamin K2 is found in smaller amounts in meat, eggs, dairy products, and fermented foods such as cheese and natto (fermented soybeans).

Pregnant women following a balanced diet that includes regular servings of vegetables typically consume well above the recommended intake. However, those with restrictive eating patterns, food aversions, or hyperemesis gravidarum may struggle to meet their needs. Women with persistent hyperemesis or sustained restrictive intake may benefit from referral to a dietitian. It is worth noting that vitamin K is relatively stable during cooking, though some loss occurs with prolonged boiling. Light exposure can degrade vitamin K in foods, so proper storage of fresh vegetables is advisable.

For women concerned about their vitamin K intake, keeping a food diary and discussing it with a midwife or GP can provide reassurance. If considering a prenatal multivitamin, check the label or consult a pharmacist about vitamin K content, as this varies between products. The focus should remain on consuming a variety of nutrient-dense foods, which naturally provides adequate vitamin K alongside other essential nutrients for pregnancy.

Vitamin K Deficiency: Risks for Mother and Baby

Vitamin K deficiency during pregnancy is uncommon in the UK but can have serious consequences when it occurs. For the mother, inadequate vitamin K impairs the synthesis of clotting factors, potentially increasing the risk of haemorrhage during delivery or postpartum. Women with pre-existing conditions affecting fat absorption—such as Crohn's disease, ulcerative colitis, coeliac disease, or those who have undergone bariatric surgery—are at higher risk of deficiency and may require monitoring. Those with intrahepatic cholestasis of pregnancy may also have altered vitamin K metabolism and might need specialist obstetric and haematology input.

Certain medications significantly interfere with vitamin K metabolism and increase deficiency risk. Anticonvulsant drugs, particularly phenytoin, phenobarbital, and carbamazepine, can reduce vitamin K levels in both mother and fetus. Similarly, prolonged use of broad-spectrum antibiotics can disrupt the intestinal bacteria that contribute to vitamin K status, though this is rarely problematic with short courses.

For the newborn, the consequences of vitamin K deficiency are more significant. Babies are born with low vitamin K stores due to limited placental transfer, minimal synthesis by immature gut bacteria, and low concentrations in breast milk. Without prophylaxis, this can lead to vitamin K deficiency bleeding (VKDB), previously known as haemorrhagic disease of the newborn. This condition can manifest as early VKDB (within 24 hours), classical VKDB (days 2–7), or late VKDB (2–12 weeks of age), with the late form potentially causing serious intracranial haemorrhage. Exclusively breastfed infants without prophylaxis are at higher risk of late VKDB.

The NHS offers all newborns vitamin K prophylaxis shortly after birth. The intramuscular injection is preferred in the UK as it provides complete protection with a single dose. Oral vitamin K is an alternative but requires multiple doses and is less effective, especially for higher-risk infants. This prophylaxis has dramatically reduced VKDB incidence. Pregnant women should be aware that maternal vitamin K status, whilst important, does not eliminate the need for neonatal prophylaxis. If you are taking medications that affect vitamin K metabolism or have a malabsorption condition, discuss this with your midwife or obstetrician, as additional monitoring may be recommended.

Vitamin K Supplementation: When Is It Needed?

Routine vitamin K supplementation is not recommended for healthy pregnant women in the UK, as dietary intake is generally sufficient. The NICE guidelines on antenatal care do not include vitamin K among the standard supplements advised during pregnancy (which are limited to folic acid and vitamin D). However, specific clinical circumstances may warrant consideration of vitamin K status, and these decisions should be made in consultation with healthcare professionals.

Women taking enzyme-inducing anticonvulsant medications (such as carbamazepine, phenytoin, phenobarbital, and primidone) have traditionally been considered at higher risk of vitamin K deficiency. However, current UK guidance, including RCOG Green-top Guideline 68 on epilepsy in pregnancy, does not routinely recommend maternal vitamin K supplementation due to limited evidence. The focus instead is on ensuring all newborns receive vitamin K prophylaxis at birth, preferably as an intramuscular injection.

Women with chronic malabsorption disorders, those who have undergone bariatric surgery, or those with liver disease affecting clotting factor synthesis may require specialist assessment of their vitamin K status. Similarly, pregnant women on anticoagulant therapy may need specialist input regarding vitamin K management.

If supplementation is considered necessary in individual cases, it should be prescribed and monitored by a healthcare professional under specialist supervision. Excessive vitamin K intake, whilst generally considered safe, has not been extensively studied in pregnancy.

When to contact your healthcare provider:

• If you are taking anticonvulsant medications and have questions about vitamin K

• If you have a diagnosed malabsorption condition and are concerned about nutrient deficiencies

• If you experience unusual bruising or bleeding during pregnancy

• If you have questions about your diet and whether it provides adequate vitamin K

Seek urgent medical attention via maternity triage/assessment unit, NHS 111, or 999 as appropriate if you experience heavy vaginal bleeding, persistent nose/gum bleeding, black/bloody stools, or extensive bruising.

For most pregnant women, focusing on a balanced diet rich in green vegetables, alongside the recommended folic acid and vitamin D supplements, provides optimal nutrition without the need for additional vitamin K supplementation. If you experience any suspected side effects from vitamin K medicines (including neonatal prophylaxis), these can be reported via the MHRA Yellow Card scheme.

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