FOLIC ACID AND VITAMIN B12 LEVELS IN PREGNANCY AND THEIR RELATION TO MEGALOBLASTIC ANAEMIA

Vitamin B12 status in health and disease: a critical review. Diagnosis of deficiency and insufficiency - clinical and laboratory pitfalls

Vitamin B₁₂ (cobalamin) is an essential cofactor for two metabolic pathways. It is obtained principally from food of animal origin. Cobalamin becomes bioavailable through a series of steps pertaining to its release from dietary protein, intrinsic factor-mediated absorption, haptocorrin or transcobalamin-mediated transport, cellular uptake, and two enzymatic conversions (via methionine synthase and methylmalonyl-CoA-mutase) into cofactor forms: methylcobalamin and adenosylcobalamin. Vitamin B₁₂ deficiency can masquerade as a multitude of illnesses, presenting different perspectives from the point of view of the hematologist, neurologist, gastroenterologist, general physician, or dietician. Increased physician vigilance and heightened patient awareness often account for its early presentation, and testing sometimes occurs during a phase of vitamin B₁₂ insufficiency before the main onset of the disease. The chosen test often depends on its availability rather than on the diagnostic performance and sensitivity to irrelevant factors interfering with vitamin B₁₂ markers. Although serum B₁₂ is still the most commonly used and widely available test, diagnostics by holotranscobalamin, serum methylmalonic acid, and plasma homocysteine measurements have grown in the last several years in routine practice. The lack of a robust absorption test, coupled with compromised sensitivity and specificity of other tests (intrinsic factor and gastric parietal cell antibodies), hinders determination of the cause for depleted B₁₂ status. This can lead to incorrect supplementation regimes and uncertainty regarding later treatment. This review discusses currently available knowledge on vitamin B₁₂, informs the reader about the pitfalls of tests for assessing its deficiency, reviews B₁₂ status in various populations at different disease stages, and provides recommendations for interpretation, treatment, and associated risks. Future directions for diagnostics of B₁₂ status and health interventions are also discussed.

Micronutrients in Multiple Pregnancies-The Knowns and Unknowns: A Systematic Review

Maternal diet and nutritional status are of key importance with regard to the short- and long-term health outcomes of both the mother and the fetus. Multiple pregnancies are a special phenomenon in the context of nutrition. The presence of more than one fetus may lead to increased metabolic requirements and a faster depletion of maternal macro- and micro- nutrient reserves than in a singleton pregnancy. The aim of this systematic review was to gather available knowledge on the supply and needs of mothers with multiple pregnancies in terms of micronutrients and the epidemiology of deficiencies in that population. It was constructed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses Statement (PRISMA). The authors conducted a systematic literature search with the use of three databases: PubMed/MEDLINE, Scopus and Embase. The last search was run on the 18 October 2020 and identified 1379 articles. Finally, 12 articles and 1 series of publications met the inclusion criteria. Based on the retrieved studies, it may be concluded that women with multiple pregnancies might be at risk of vitamin D and iron deficiencies. With regard to other microelements, the evidence is either inconsistent, scarce or absent. Further in-depth prospective and population studies are necessary to determine if nutritional recommendations addressed to pregnant women require adjustments in cases of multiple gestations.

How I treat anemia in pregnancy: iron, cobalamin, and folate

Anemia of pregnancy, an important risk factor for fetal and maternal morbidity, is considered a global health problem, affecting almost 50% of pregnant women. In this article, diagnosis and management of iron, cobalamin, and folate deficiencies, the most frequent causes of anemia in pregnancy, are discussed. Three clinical cases are considered. Iron deficiency is the most common cause. Laboratory tests defining iron deficiency, the recognition of developmental delays and cognitive abnormalities in iron-deficient neonates, and literature addressing the efficacy and safety of IV iron in pregnancy are reviewed. An algorithm is proposed to help clinicians diagnose and treat iron deficiency, recommending oral iron in the first trimester and IV iron later. Association of folate deficiency with neural tube defects and impact of fortification programs are discussed. With increased obesity and bariatric surgery rates, prevalence of cobalamin deficiency in pregnancy is rising. Low maternal cobalamin may be associated with fetal growth retardation, fetal insulin resistance, and excess adiposity. The importance of treating cobalamin deficiency in pregnancy is considered. A case of malarial anemia emphasizes the complex relationship between iron deficiency, iron treatment, and malaria infection in endemic areas; the heightened impact of combined etiologies on anemia severity is highlighted.

Prevalence of vitamin B-12 insufficiency during pregnancy and its effect on offspring birth weight: a systematic review and meta-analysis

BACKGROUND

Vitamin B-12 and folate are micronutrients essential for normal embryogenesis. Vitamin B-12 insufficiency in pregnancy is high in certain parts of the world, such as India, and although this has been linked to low birth weight (LBW) in these populations, the relation between vitamin B-12 and birth weight (BW) elsewhere is unknown.

OBJECTIVES

We performed a systematic review to assess 1) the worldwide prevalence of vitamin B-12 insufficiency in pregnancy and 2) its association with BW.

DESIGN

A search of 5 electronic databases was performed to identify eligible articles. Random-effects meta-analysis was conducted according to geographic regions and pregnancy trimesters for the prevalence subreview and by categorical measures of BW.

RESULTS

A total of 57 and 23 articles were included for the prevalence and BW subreviews, respectively. The pooled estimates of vitamin B-12 insufficiency were 21%, 19%, and 29% in the first, second, and third trimesters, respectively, with high rates for the Indian subcontinent and the Eastern Mediterranean. The large heterogeneity between studies was partially addressed by creating a standardized score for each study (mean vitamin B-12 insufficiency ÷ cutoff value), which internally corrected for geographic region, trimester, and assay type. Twelve of the 13 longitudinal studies included showed a decrease in mean or median vitamin B-12 across trimesters. Pooled analysis showed nonsignificantly lower maternal vitamin B-12 concentrations in LBW than in normal-BW infants and higher odds of LBW with lower vitamin B-12 values (adjusted OR: 1.70; 95% CI: 1.16, 2.50), but studies from India largely contributed to the latter.

CONCLUSIONS

Our review indicates that vitamin B-12 insufficiency during pregnancy is common even in nonvegetarian populations and that concentrations of vitamin B-12 decrease from the first to the third trimester. There is no consistent association between vitamin B-12 insufficiency and LBW. However, given the long-term risks of LBW, this observation warrants further cohort studies and randomized controlled trials.

A longitudinal study of maternal folate and vitamin B12 status in pregnancy and postpartum, with the same infant markers at 6 months of age

Folate and vitamin B12 are involved in homocysteine metabolism and are critical to the methylation of DNA. We aimed to assess plasma vitamin B12 (pB12), plasma folate (pFol), and red cell folate (rcFol) in women and their infants during pregnancy and after birth. Maternal biomarkers were tested as predictors of infant biomarkers, including plasma homocysteine (pHcy), at age 6 months. Participants (n = 153) were recruited at the John Hunter Hospital, Australia. Maternal fasting blood samples were collected at 20 and 36 weeks gestation, and at 14 and 27 weeks postpartum. Fifty healthy, term infants provided non-fasting samples at age 6 months. Plasma homocysteine data were available for 16 infants at age 6 months. Maternal pB12 concentrations fell by 16% from 20 to 36 weeks gestation, but had recovered by 14 weeks postpartum. Maternal rcFol concentrations fell by 31% from 20 weeks gestation to 27 weeks postpartum. Infants breastfed at 6 months had lower pB12 (median 159 vs. 402 pmol/L, n = 23 vs. 18, P < 0.01) and folate (median folate z-score -0.58 vs. 0.85, n = 23 vs. 17, P < 0.01), and higher pHcy (median 11.9 vs. 7.3 μmol/L, n = 8 vs. 6, P < 0.01), than those on infant formula. Maternal pregnancy pFol, but not pB12, inversely predicted infant pHcy, after adjustment for the infant's current pB12 (P = 0.04). Changes in maternal B12 and folate occur during pregnancy and after birth. Infant homocysteine metabolism may be regulated through maternal folate concentrations during pregnancy and postnatal feeding.

Effects of Folate and Vitamin B12 Deficiencies During Pregnancy on Fetal, Infant, and Child Development

The importance of folate in reproduction can be appreciated by considering that the existence of the vitamin was first suspected from efforts to explain a potentially fatal megaloblastic anemia in young pregnant women in India. Today, low maternal folate status during pregnancy and lactation remains a significant cause of maternal morbidity in some communities. The folate status of the neonate tends to be protected at the expense of maternal stores; nevertheless, there is mounting evidence that inadequate maternal folate status during pregnancy may lead to low infant birthweight, thereby conferring risk of developmental and long-term adverse health outcomes. Moreover, folate-related anemia during childhood and adolescence might predispose children to further infections and disease. The role of folic acid in prevention of neural tube defects (NTD) is now established, and several studies suggest that this protection may extend to some other birth defects. In terms of maternal health, clinical vitamin B12 deficiency may be a cause of infertility or recurrent spontaneous abortion. Starting pregnancy with an inadequate vitamin B12 status may increase risk of birth defects such as NTD, and may contribute to preterm delivery, although this needs further evaluation. Furthermore, inadequate vitamin B12 status in the mother may lead to frank deficiency in the infant if sufficient fetal stores of vitamin B12 are not laid down during pregnancy or are not available in breastmilk. However, the implications of starting pregnancy and lactation with low vitamin B12 status have not been sufficiently researched.

Folate and human reproduction

The influence of folate nutritional status on various pregnancy outcomes has long been recognized. Studies conducted in the 1950s and 1960s led to the recognition of prenatal folic acid supplementation as a means to prevent pregnancy-induced megaloblastic anemia. In the 1990s, the utility of periconceptional folic acid supplementation and folic acid food fortification emerged when they were proven to prevent the occurrence of neural tube defects. These distinctively different uses of folic acid may well be ranked among the most significant public health measures for the prevention of pregnancy-related disorders. Folate is now viewed not only as a nutrient needed to prevent megaloblastic anemia in pregnancy but also as a vitamin essential for reproductive health. This review focuses on the relation between various outcomes of human reproduction (ie, pregnancy, lactation, and male reproduction) and folate nutrition and metabolism, homocysteine metabolism, and polymorphisms of genes that encode folate-related enzymes or proteins, and we identify issues for future research.

Folate and vitamin B12 status of women in Newfoundland at their first prenatal visit

BACKGROUND

Newfoundland has one of the highest rates of neural tube defects in North America. Given the association between low maternal folic acid levels and neural tube defects, a cross-sectional study was conducted to obtain base-line data on the folate and vitamin B12 status of a sample of women in Newfoundland who were pregnant.

METHODS

Blood samples were collected between August 1996 and July 1997 from 1424 pregnant women in Newfoundland during the first prenatal visit (at approximately 16 weeks' gestation); this represented approximately 25% of the women in Newfoundland who were pregnant during this period. The samples were analysed for serum folate, vitamin B12, red blood cell folate and homocysteine.

RESULTS

Median values for serum folate, red blood cell folate and serum vitamin B12 were 25 nmol/L, 650 nmol/L and 180 pmol/L, respectively. On the basis of the interpretive criteria used for red blood cell folate status, 157 (11.0%) of the 1424 women were deficient (< 340 nmol/L) and a further 180 (12.6%) were classified as indeterminate (340-420 nmol/L). Serum homocysteine levels, measured in subsets of the red blood cell folate status groups, supported the inadequate folate status. Serum vitamin B12 levels of 621 (43.6%) women were classified as deficient or marginal; however, the validity of the interpretive criteria for pregnant women is questionable.

INTERPRETATION

A large proportion of pregnant women surveyed in Newfoundland in 1997 had low red blood cell folate levels.

Evaluation of low serum vitamin B(12) in the non-anaemic pregnant patient

Low serum vitamin B(12) concentrations in pregnancy may not indicate true megaloblastic anaemia. In the present study we compared biochemical indices of vitamin B(12) deficiency (serum homocysteine and urine methylmalonic acid) in non-anaemic pregnant women with and without low serum vitamin B(12) concentrations. The groups were matched for age, parity and gestational age. No differences were found, and all values were within normal range. These results suggest that the measurement of low serum B(12) concentrations in pregnant women should be followed by analysis at the biochemical level before vitamin B(12) injections are started.

PRACTICAL EVALUATION OF THE FIGLU TEST IN PREGNANCY WITH SPECIAL REFERENCE TO THE WHITE CELL CHANGES

Using slight modifications to the method of Kohn, Mollin, and Rosenbach (1961) the histidine loading test has been carried out in 210 pregnant women. Seventy per cent. of the cases showed complete haematological correlation and this rose to 87% when marrow puncture was performed. False positive results occurred in some cases showing active erythropoiesis in response to iron therapy. False negative results were noted when other complications in addition to anaemia were present, and it was felt that these might interfere with the metabolism of histidine. In some cases the histidine test anticipated the haematological change.Seventy-seven per cent. of women with multiple pregnancies showed evidence of folic acid deficiency. Only in a few cases was the test positive before the 25th week of pregnancy. These were either cases of multiple pregnancy, haemolytic anaemia, malabsorption syndrome, or women with a recent history of megaloblastic anaemia of pregnancy. The test appears to confirm the significance of white cell changes as an indication of folic acid deficiency in pregnancy.

Serum ferritin, folate and cobalamin levels and their correlation with anemia in normal full-term pregnant women

Serum ferritin, folate, cobalamin and hemoglobin concentrations were determined by radioimmunoassay, radioisotopic assay, radioassay and an automated hematology analyser respectively, and then analysed in 221 normal full-term pregnant women in order to evaluate the incidence and the prevalence of nutritional anemia in pregnancy. None of them had received any hematonic during their pregnancy. Their mean age was 27.68 years and the mean duration of pregnancy was 39.51 weeks. Twenty-three (10.41%) of these previously non-anemic pregnant women had clinical anemia after full-term pregnancy. Of the 23 women, 11 (47.83%) had iron-deficiency anemia, with serum ferritin less than 12 micrograms/l; another 11 women had some degree of iron depletion, with serum ferritin less than 20 micrograms/l. So in 22 of the 23 anemic women (95.65%) the cause of anemia may correlate to iron depletion. The remaining one had folate-deficiency anemia. No pure cobalamin deficiency anemia was found in this study. Among the 198 non-anemic normal full-term pregnant women, 92 (46.46%) had iron depletion (serum ferritin less than 20 micrograms/l), of whom 35 (17.68%) had severe iron deficiency, with serum ferritin less than 12 micrograms/l. Another 3 had folate deficiency and 3 had cobalamin deficiency. By including all the anemic and non-anemic pregnant women, 114 (51.58%) of them had some degree of iron depletion. In other words, pregnancy can produce a considerable degree of iron depletion in more than half of the previously non-anemic women.

Anticonvulsants, folate levels, and pregnancy outcome: a prospective study

Folate levels in serum and red cells, as determined by a microbiological assay using Lactobacillus casei, and plasma anticonvulsant concentrations were monitored concurrently in nonpregnant (50 subjects) and pregnant (49 pregnancies in 46 subjects) epileptic women. Twenty-three (46%) nonpregnant women had subnormal serum folate levels and 4 nonpregnant women (8%) showed subnormal red cell folate levels. In pregnant women not taking folate supplements, the incidence of folate deficiency increased as the pregnancy advanced. Pregnant women taking folate supplements achieved normal or supranormal blood folate concentrations. In both nonpregnant and pregnant women, serum and red cell folate levels were inversely correlated with plasma concentrations of phenytoin and of phenobarbital, and with the number of anticonvulsants. In 49 pregnancies, there were 10 abnormal outcomes (20.4%): 4 spontaneous abortions (8.2%) and 6 children with major congenital malformations (12.2%). Blood folate levels were significantly lower in pregnancies with an abnormal outcome than in those with a normal outcome. The results suggest a dose-response relationship among anticonvulsants, folate, and adverse pregnancy outcome.

Disorders of cobalamin metabolism

Recent developments in our knowledge of the biochemistry and metabolism of cobalamin have given us some insight into clinical disorders. N2O, which easily induces cobalamin deficiency, both in vivo and in vitro, has greatly contributed to the investigation of the cobalamin deficient state, especially in relation to folate and amino acid metabolism. Demonstration of the cobalamin analog in human serum and a new enzyme which requires cobalamin as a coenzyme has led to recent increased interest in this field. The disorders of cobalamin metabolism will be summarized briefly as well as those areas currently of particular interest.

Iron, folate, and vitamin B 12 nutrition in pregnancy: a study of 1000 women from southern India

As part of a WHO collaborative programme the prevalence of anaemia was studied and the serum concentrations of iron, folate, and vitamin B(12) were measured in 1 000 pregnant women from southern India. The results of the study show a high prevalence of anaemia, resulting from iron and folate deficiency with iron deficiency predominating. Interrelationships between these nutrients and their effect on pregnancy and the fetus were investigated. The results indicate that, in comparison with populations in developed countries, there was a high prevalence of iron and vitamin B(12) deficiency in the community, but the state of folate nutrition was similar to that found elsewhere.

Smoking in pregnancy and vitamin B 12 metabolism

In pregnancy the level of serum vitamin B(12) is lower in women who smoke than in non-smokers. This finding occurs independently of social class, parity, or level of haemoglobin. In addition, the mean serum B(12) level tends to be less in women who are anaemic and is less in those women who have smaller babies. These findings may be an effect of the cyanide content of tobacco smoke, since cyanide may be detoxified by a mechanism which depletes the stores of vitamin B(12) in the body.

Relation between maternal and infant blood folate activities

The relation between maternal and cord blood folate activity was investigated in a group of 110 primigravidae and their infants. Approximately half of these mothers had received folic acid supplements during their pregnancy, and the effects of this on infant blood folate levels at birth and at 6 weeks were also studied. In unsupplemented pregnancies there was a significant relation between infant and maternal blood folate levels at delivery. The results of folic acid supplementation during pregnancy were reflected by higher cord blood values, but 6 weeks after delivery infant plasma folate levels were essentially the same in both groups and independent of maternal supplies before delivery.

Cobalamins in human pregnancy and lactation

Samples of maternal and foetal blood and of human milk, cow's milk, and dried cow's milk have been analysed for cobalamins by chromatography and bioautography. Plasma cobalamins in late pregnancy and after delivery differed quantitatively from those in healthy non-pregnant women. Differences in the proportions of plasma cobalamins were also observed between mothers and their newborn infants. The findings suggest that methylcobalamin may be a more labile plasma form of the vitamin than 5-deoxyadenosyl cobalamin. Breast milk from healthy mothers contained more deoxyadenosylcobalamin and proportionately less methylcobalamin than their plasma. Cyanocobalamin given parenterally to lactating women was detected in the plasma, and high concentrations appeared unchanged in the milk. The B(12) in fresh cow's milk was found to be largely 5-deoxyadenosyl cobalamin whereas dried milk contained only hydroxocobalamin and a little cyanocobalamin. The nutritional implications of the findings, and their bearing on problems of cobalamin transport, are discussed.

Megaloblastic anaemia of pregnancy: a clinical and laboratory study with particular reference to the total and labile serum folate levels

It has been shown that the incidence of megaloblastic anaemia in a group of 463 randomly selected pregnant women receiving iron was 12 times as high as in a control group of 235 pregnant women receiving iron and folic acid. The incidence of all types of anaemia in the women receiving iron alone was more than three times the incidence in those having iron and folic acid. Some women who were not anaemic or who had normoblastic anaemia had serum folate levels in the same range as the women with megaloblastic anaemia, but none of the women with megaloblastic anaemia had high serum folate levels. The labile fraction of the serum folate was no more reliable than the total serum folate as a diagnostic criterion of megaloblastic erythropoiesis in the individual case. The blood group distribution in the women with megaloblastic anaemia was the same as in the general population. Babies born to mothers with megaloblastic anaemia tended to be smaller than the rest, although there was no difference in the placental weights. The significance of these findings is discussed.

Nutritional anemia and megaloblastosis in pregnancy

Macrogranulocytic and/or erythroid megaloblastic bone marrow changes which could not be accurately predicted from the hematologic findings in the blood were present in 25% of 305 mildly to moderately anemic pregnant women attending a public antepartum clinic in Montreal. Iron deficiency was the primary cause of anemia in most instances. Serum folate activity of less than 4.1 ng./ml. and/or serum vitamin B(12) levels of less than 100 pg./ml. were present in 90% of the 77 patients having these bone marrow changes, whereas approximately one-third of 228 patients with normoblastic marrow had these low values. Red cell folate did not correlate as well as serum folate activity with bone marrow changes. After treatment with oral folic acid in the range of 0.2 mg. to 0.8 mg., daily, for seven to 14 days, the megaloblastic and macrogranulocytic changes in patients with low serum folate activity and normal serum vitamin B(12) values disappeared in 15 of 21 patients. Of five women having both low folate and vitamin B(12) values, three failed to respond and two showed only partial improvement after 0.4 mg. of folic acid daily, per os, for 10 days. The average diet of these anemic women was suboptimal in folate and in iron.

Effect of ascorbic acid on the serum folic acid estimation

Ascorbic acid added to the basal medium increased the growth response of Lactobacillus casei in folic acid standards. The effect in the serum extracts was not marked, resulting in lowered serum folic acid estimations. However, results obtained on prolonged incubation were similar whether ascorbic acid was added or not. The presence or absence of ascorbic acid and variation of the incubation period may account for differences in reported normal ranges of serum folic acid levels.

An account of 335 cases of megaloblastic anaemia of pregnancy and the puerperium

The incidence of megaloblastic anaemia in pregnancy and the puerperium in north Staffordshire has steadily declined as a result of prophylaxis with folic acid. In the presence of advanced folic acid deficiency and with a florid megaloblastic marrow, the anaemia is usually severe, but in many patients the disease is relatively mild and the degree of anaemia is determined more by blood loss or associated iron deficiency than by the megaloblastosis. Microscopic examination of marrow films is still the most reliable method of diagnosis, although estimation of the labile serum folate has produced a 95% correlation with the marrow findings. There are three main factors which operate in the pathogenesis of megaloblastic anaemia in pregnancy and the puerperium. First, the maternal stores of folic acid are used up by the growing foetus, and this process is accelerated in multiple pregnancies, after haemorrhage, or in women with haemolytic anaemia. Secondly, an insufficient intake of folic acid, due to poor diet in pregnancy, plays a part in many cases. The third, and possibly the most important, factor is an absorption defect. Folic acid absorption is usually impaired in established cases, and this can still be demonstrated years later in a majority of patients, when they are neither pregnant nor anaemic. More than 20% of all cases also show abnormal fat absorption. An inherited defect in folic acid absorption may also explain why certain women appear to be constitutionally predisposed to megaloblastic anaemia of pregnancy and the puerperium, as shown by the abnormal blood group distribution in these patients and by the tendency of megaloblastic anaemia to recur not only in subsequent pregnancies, but, as in six of our cases, following other kinds of stress. The significance of commonly associated conditions like pre-eclampsia and infection is still incompletely understood. Although the treatment of megaloblastic anaemia is simple and effective, the main emphasis should be placed on prophylaxis by administering folic acid to all pregnant women.

Folate Activity in Malignant Blood Diseases

Basal serum folate activity, serum folate clearance and folate output in the urine after folic acid loading, urocanic acid and formiminoglutamic acid output in the urine after histidine loading were determined on 27 patients with malignant blood diseases in therapeutic remission. The mean values for basal serum folate activity and for serum folate activity and urinary folate output after folic acid loading were significantly lower than normal, both in chronic myeloid leukemia and in Hodgkin's disease. On the contrary, in chronic lymphatic leukemia only after folic acid loading urinary folate output was significantly lower than normal. The median values for urinary excretion of histidine derivatives after histidine loading was higher than normal in Hodgkin's disease and in chronic lymphatic leukemia. Folate deficiency was observed in 16 out of the 27 patients under study. Comparative analysis of multiple test results showed different response patterns which can be attributed to different types of deficiency, namely tetrahydrofolate deficiency from primary folate deficiency and possibly tetrahydrofolate deficiency from folate metabolic abnormalities. Folate deficiency appeared to correlate with the activity of disease when expressed by such parameters as performance status and erythrocyte sedimentation rate. This applies to all patients as a group, and, as far as performance status is concerned, to the chronic lymphatic leukemia patients as a subgroup. Folate deficiency did not appear to correlate with other parameters of disease nor to induce, in the majority of patients, the typical hematologic features. Folate deficiency in malignant blood diseases is likely to be somehow related to the abnormal cell proliferation, through several possible mechanisms which are analysed and discussed.

Enzymatic release of folate activity from the red cells in megaloblastic anaemia of pregnancy

The content of folate activity precursors in washed red cells and the enzymatic plasma factor activity, necessary for the release of folate from the precursors, were studied in normal subjects and in patients with megaloblastic anaemia of pregnancy. Subjects with megaloblastic anaemia of pregnancy had a significantly reduced folate activity precursor content, and 14 subjects (58%) had significantly low plasma factor activity, which in at least four subjects may have been due to the presence of inhibitors. This study indicates that impaired activity of the plasma factor may play a part in the aetiology of megaloblastic anaemia of pregnancy.