A Newborn Blood Test That Can Also Help the Mother: What Families Should Know About Vitamin B12

What three European studies — from Milan, from Austria and Switzerland, and from Prague — tell parents about low vitamin B12 in babies, what the heel-prick test can and cannot find, and why the mother's health is part of the answer

Why a vitamin in the mother's body matters so much to a new baby

Vitamin B12 is a nutrient that babies need to build healthy blood and a growing brain. Before birth, a baby stores the B12 it receives from its mother, and after birth a breastfed baby continues to get B12 through breast milk. When a mother is low in B12 — because of her diet, a pregnancy illness, or a stomach or bowel condition that stops her body absorbing it — her baby can be born with low stores and slowly run short over the first months of life. Low B12 is treatable, and some newborn blood-spot programmes can now pick it up in the first days of life, but the test does not catch every baby, and the story almost always leads back to the mother.

Three studies, one question

This article brings together three studies published within about a year of each other. The first comes from Vittore Buzzi Children's Hospital in Milan, Italy, where Tosi and colleagues looked at the diets of 107 mothers whose babies had been flagged by the regional newborn blood test as having low B12 passed on from the mother [1]. The second, led from the University Children's Hospital Zurich and the Medical University of Innsbruck, looked in the opposite direction: of 48 babies in Austria and Switzerland who actually became ill with low B12 in their first year, how many would the newborn test have found at birth [2]? The third, a trial run at four university hospitals in Prague, Czech Republic, added a purpose-built B12 check to the routine newborn blood test for three years and also examined the mothers of the babies it found [3]. Read together, the three studies agree that a baby's B12 reflects the mother's, but they paint different pictures of how much the newborn test can do on its own.

How families and doctors used to meet this problem

For most of the last half-century, low B12 in babies was discovered only after a child became unwell. The condition was first described in detail in 1978, in a breastfed baby whose mother followed a strict vegetarian diet; the baby had anaemia (too few healthy red blood cells), abnormal acids building up in the blood and urine, and problems with the nervous system [4]. Doctors following such children later found that some nervous-system problems could last well beyond the illness itself [5], and researchers came to understand that breastfed babies depend heavily on the B12 they stored before birth and on the B12 in breast milk [6].

One reason the diagnosis was often late is that the most obvious sign doctors look for — a particular kind of anaemia — is frequently missing. In an earlier study of 40 breastfed babies with low B12, carried out by the same Prague team behind the new pilot, only 28% had that telltale anaemia [7]. Families might instead notice a baby who was unusually floppy, feeding poorly, sleepy, or not gaining weight, often around the middle of the first year.

Things began to change when newborn screening laboratories adopted a technology called tandem mass spectrometry, which measures many substances in the single drop of blood taken from a baby's heel in the first days of life. It was introduced to find rare inherited conditions, but laboratories in the United States [8] and Italy [9] noticed that it sometimes flagged babies who simply had low B12 inherited from a low-B12 mother. Germany then began looking for low B12 on purpose and linked earlier treatment to better outcomes [10]; German data also showed that babies were diagnosed with low B12 about four times more often in populations without screening than in those with it [11]. In Catalonia, Spain, laboratories showed that a second, more specific test on the same drop of blood could cut down on false alarms [12]. Even so, countries today do very different things: some screen for B12, some find it only by accident, and some, such as Switzerland, do not look for it at all [2].

Who the mothers were: the Milan study

The Milan study helps answer a question many parents ask first: "Was it something I ate?" [1]. Specially trained dietitians asked each of the 107 mothers what she had eaten during pregnancy and what supplements she had taken. A common assumption is that low B12 happens mainly to mothers who avoid all animal foods. That was not what the study found. Seventy-one per cent of the mothers ate meat and fish, and only one mother was vegan.

Yet very few were getting enough B12. European experts suggest an adequate intake of 4.5 micrograms of B12 a day in pregnancy; these mothers averaged 2.6 micrograms, and only about one in five reached the recommended amount even when supplements were counted. Almost all the mothers took some kind of pregnancy supplement, but only 15% took one containing B12, and always as part of a multivitamin. For about three-quarters of mothers, low intake from food was the main explanation. Around one in ten had suffered severe, prolonged vomiting in pregnancy (a condition called hyperemesis gravidarum), and a smaller number had signs of an immune condition affecting the stomach. The reassuring news is that the babies in this study, once treated, showed no significant problems with growth or development at their check-ups up to 12 months of age.

The babies the test did not catch: the Austria–Switzerland study

The second study is a reminder that a normal newborn test is not a guarantee [2]. The researchers gathered 48 babies from Austrian and Swiss hospitals who became ill with low B12 in their first year, between 2012 and 2022. Their first symptoms appeared, on average, at about six months of age. The team then took each baby's original newborn test results and asked whether Austria's current screening method would have flagged them.

For 43 babies the results were available, and only four of the 43 — about one in eleven — would have been flagged at birth. Most of the babies who later became ill had passed their newborn test. The good news is that most of them recovered well: 38 recovered fully, although four had lasting developmental difficulties. Looking at the mothers, most ate a mixed diet, six were vegan, and some had stomach or bowel conditions, such as inflammation of the stomach lining or inflammatory bowel disease, that make B12 harder to absorb. The authors concluded that newborn testing alone cannot prevent most serious cases, and that pregnant women themselves should be checked for low B12. A similar study from Norway had earlier reached much the same conclusion [13].

A test designed with both baby and mother in mind: the Prague pilot

The Prague team built its approach with these limits in mind [3]. Parents at four hospitals were offered an extra B12 check on the heel-prick sample their baby was already having, with no additional needle. Parents of 34,302 babies agreed. The laboratory used a first set of markers to spot possible cases, then ran a second, more precise test for a substance called methylmalonic acid on the same blood spot before calling any family back, using a method adapted from the Catalonian approach [12].

This two-step design mattered for families. Out of more than 34,000 babies, only nine families received a call-back, and eight of those nine babies really did have low B12 — about one baby in every 4,200. Put another way, a family who got a call-back from this programme could be fairly confident it was not a false alarm. All eight babies were treated with vitamin B12 drops given by mouth, and the extra laboratory test cost about €1.61 per baby screened.

The most striking part of the Prague study concerns the mothers. When they were tested, half turned out to be low in B12 themselves. A special absorption test showed that some mothers could not properly absorb B12 from food, while all the babies absorbed it normally. Three mothers were found to have long-standing inflammation of the stomach lining that nobody had known about, and two had early changes in the stomach that needed regular monitoring; in one of them, an early-stage cancer was later found. In other words, a routine test on a newborn baby led doctors to an important diagnosis in the mother.

What this means for families

If your baby's newborn screen shows low B12, the three studies suggest this is usually a sign that the mother is low too, and that it is treatable. It is worth asking whether the mother should also be tested, especially if she has had severe vomiting in pregnancy, stomach or bowel problems, weight-loss surgery, or a diet low in animal foods. Being called back is stressful — the Austria–Switzerland researchers cite an Italian study in which most parents described high levels of distress after such a call [2] — so it may help to know that, in a well-designed programme like Prague's, a call-back usually leads to simple treatment and to care for the mother as well.

If your baby's newborn test was normal, the Austria–Switzerland study is a reminder that low B12 can still develop later, particularly in breastfed babies whose mothers have low stores. A baby around the middle of the first year who seems unusually floppy, pale, sleepy, or is falling off their growth curve deserves a check-up, and it is reasonable to mention the mother's diet and health history to the baby's doctor.

For mothers, the Milan study shows that eating meat and fish does not guarantee enough B12 in pregnancy. Its authors recommend that nutritional advice and, where needed, supplements begin before conception. It is honest to add that research has not yet firmly shown whether routine B12 supplements in pregnancy improve outcomes for babies [14], so decisions are best made with a doctor, midwife or dietitian.

What researchers are working on next

Several questions remain open. Researchers do not yet know how many babies with low B12 a test like Prague's misses, because babies with a normal result were not followed up. They also want to learn whether checking and treating mothers during pregnancy prevents illness in babies, and whether B12 screening pays for itself: an Italian estimate put the cost of caring for one affected newborn at about €3,579 [15], far more than the Prague test cost per baby. Taken together, these three studies suggest that the best protection for babies may come from treating the newborn test and the mother's pregnancy care as partners — the blood spot as a safety net, and good B12 care in pregnancy as the first line of defence.

References

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  2. Kaufman C, Margreitter J, Herle M, et al. Newborn Screening Alone Cannot Prevent Most Cases of Severe Vitamin B12 Deficiency in the First Year of Life. Nutrients. 2025;17(22):3583. doi:10.3390/nu17223583 ↩
  3. Stanovský S, Bártl J, Chrastina P, et al. Pilot Newborn Screening for Vitamin B12 Deficiency in the Czech Republic: Results and Detailed Studies on Identified Babies and Their Mothers. Int J Neonatal Screen. 2026;12(2):30. doi:10.3390/ijns12020030 ↩
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