High vitamin A intake in early pregnancy and major malformations: a multicenter prospective controlled study

Scientific opinion on the tolerable upper intake level for preformed vitamin A and β-carotene

Following two requests from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver a scientific opinion on the revision of the tolerable upper intake level (UL) for preformed vitamin A and β-carotene. Systematic reviews of the literature were conducted for priority adverse health effects of excess vitamin A intake, namely teratogenicity, hepatotoxicity and endpoints related to bone health. Available data did not allow to address whether β-carotene could potentiate preformed vitamin A toxicity. Teratogenicity was selected as the critical effect on which to base the UL for preformed vitamin A. The Panel proposes to retain the UL for preformed vitamin A of 3000 μg RE/day for adults. This UL applies to men and women, including women of child-bearing age, pregnant and lactating women and post-menopausal women. This value was scaled down to other population groups using allometric scaling (body weight0.75), leading to ULs between 600 μg RE/day (infants 4-11 months) and 2600 μg RE/day (adolescents 15-17 years). Based on available intake data, European populations are unlikely to exceed the UL for preformed vitamin A if consumption of liver, offal and products thereof is limited to once per month or less. Women who are planning to become pregnant or who are pregnant are advised not to consume liver products. Lung cancer risk was selected as the critical effect of excess supplemental β-carotene. The available data were not sufficient and suitable to characterise a dose-response relationship and identify a reference point; therefore, no UL could be established. There is no indication that β-carotene intake from the background diet is associated with adverse health effects. Smokers should avoid consuming food supplements containing β-carotene. The use of supplemental β-carotene by the general population should be limited to the purpose of meeting vitamin A requirements.

Contribution of Different Food Types to Vitamin A Intake in the Chinese Diet

Vitamin A is a fat-soluble micronutrient that is essential for human health. In this study, the daily vitamin A intake of Chinese residents was evaluated by investigating the vitamin A content of various foods. The results show that the dietary intake of vitamin A in common foods was 460.56 ugRAE/day, which is significantly lower than the recommended dietary reference intake of vitamin A (800 ugRAE/day for adult men and 700 ugRAE/day for adult women). Vegetables contributed the most to daily vitamin A dietary intake, accounting for 54.94% of vitamin A intake (253.03 ugRAE/day), followed by eggs, milk, aquatic products, meat, fruit, legumes, coarse cereals, and potatoes. Therefore, an increase in the vitamin A content of vegetables and the fortification of vegetable oils with vitamin A are effective ways to increase vitamin A intake to meet the recommended dietary guidelines in China. The assessment results support the design of fortified foods.

Retinoic acid (all-trans) presents antioxidant properties within human ovary and reduces progesterone production by human granulosa cells

Both vitamin A and E support female reproduction and embryonic development. These vitamins have been associated with decreased fertility or failure to end the pregnancy in animals. An observational study was conducted on follicular fluid (FF) samples to determine the concentrations of fat-soluble vitamins of women undergoing in vitro fertilization and its correlation with assisted reproductive technology characteristics and pregnancy outcomes. Moreover, the effects of all-trans-retinoic acid (atRA) and alpha-tocopherol on granulosa cell viability, apoptosis, autophagy and hormonal production were evaluated. No association was identified between fat-soluble vitamin concentrations in FF and infertility aetiology, body mass index or woman's age. There were differences in follicular antioxidant profiles and ovarian response stimulation. In vitro evaluation of atRA and alpha-tocopherol reveals that, at physiological concentrations, both compounds may affect the viability of granulosa cells. In addition, these compounds are able to protect granulosa cells from oxidative stress, as well as to affect estradiol and progesterone production. Our data suggest that atRA and alpha-tocopherol levels should be well controlled as they may have implications in the function and viability of granulosa cells and highlights retinol as a marker of the oxidative defenses within ovary environment.

Vitamin A fortification: Recent advances in encapsulation technologies

Vitamin A is an essential micronutrient whose deficiency is still a major health concern in many regions of the world. It plays an essential role in human growth and development, immunity, and vision, but may also help prevent several other chronic diseases. The total amount of vitamin A in the human diet often falls below the recommended dietary allowance of approximately 900-1000 μ $ \umu $ g/day for a healthy adult. Moreover, a significant proportion of vitamin A may be degraded during food processing, storage, and distribution, thereby reducing its bioactivity. Finally, the vitamin A in some foods has a relatively low bioavailability, which further reduces its efficacy. The World Health Organization has recommended fortification of foods and beverages as a safe and cost-effective means of addressing vitamin A deficiency. However, there are several factors that must be overcome before effective fortified foods can be developed, including the low solubility, chemical stability, and bioavailability of this oil-soluble vitamin. Consequently, strategies are required to evenly disperse the vitamin throughout food matrices, to inhibit its chemical degradation, to avoid any adverse interactions with any other food components, to ensure the food is palatable, and to increase its bioavailability. In this review article, we discuss the chemical, physical, and nutritional attributes of vitamin A, its main dietary sources, the factors contributing to its current deficiency, and various strategies to address these deficiencies, including diet diversification, biofortification, and food fortification.

Environmental Risk Factors for Congenital Heart Disease

Congenital heart disease (CHD) has many forms and a wide range of causes. Clinically, it is important to understand the causes. This allows estimation of recurrence rate, guides treatment options, and may also be used to formulate public health advice to reduce the population prevalence of CHD. The recent advent of sophisticated genetic and genomic methods has led to the identification of more than 100 genes associated with CHD. However, despite these great strides, to date only one-third of CHD cases have been shown to have a simple genetic cause. This is because CHD can also be caused by oligogenic factors, environmental factors, and/or gene-environment interaction. Although solid evidence for environmental causes of CHD have been available for almost 80 years, it is only very recently that the molecular mechanisms for these risk factors have begun to be investigated. In this review, we describe the most important environmental CHD risk factors, and what is known about how they cause CHD.

Maternal drug use and the risk of anorectal malformations: systematic review and meta-analysis

Background

Origin of anorectal malformations (ARM) are considered multifactorial. Several genetic and non-genetic risk factors are discussed in literature. Maternal periconceptional medical drug use as possible risk factor, however, has not been reviewed systematically.

Methods

Studies published between 1977 and April 2017 were reviewed through systematic search in PubMed, ISI Web of Knowledge and Scopus databases. Furthermore, related and cross-referencing publications were reviewed. Pooled odds ratios (95% confidence intervals) were determined to quantify associations of maternal periconceptional use of folic acid, multivitamins, anti-asthma medication (separated in any anti-asthma medication, inhaled corticosteroids and salbutamol), thyroid hormone supplements, psychiatric drugs (separated in antidepressants, any selective serotonin reuptake inhibitors [SSRI], sertraline, citalopram, fluoxetine, paroxetine, hypnotics and benzodiazepine) and aspirin with ARM using meta-analyses.

Results

Thirty-seven studies that reported on the association between maternal periconceptional drug intake and infants born with ARM were included in this review. These were conducted in the United States of America (n = 14), Sweden (n = 6), Hungary (n = 5), Germany (n = 3), the Netherlands (n = 3), Denmark (n = 2), France (n = 2), Norway (n = 1) and the UK (n = 1). However, only few of these studies reported on the same risk factors. Studies were heterogeneous with respect to case numbers, period ingestion of medical drug use, control selection and adjustment for covariates. Consistently increased risks were observed for any anti-asthma medication, and hypnotics and benzodiazepine, but not for folic acid, multivitamins, inhaled corticosteroids, salbutamol, thyroid hormone supplements, antidepressants, any SSRI, sertraline, citalopram, fluoxetine, paroxetine and aspirin. In meta-analyses, pooled odds ratios (95% confidence intervals) for any anti-asthma medication, and hypnotics and benzodiazepine were 1.64 (1.22–2.21), and 2.43 (1.03–5.73), respectively.

Conclusion

Evidence on maternal drug use before conception and during pregnancy as risk factor for ARM from epidemiological studies is still very limited. Nevertheless, the few available studies indicate any anti-asthma medication, and hypnotics and benzodiazepine to be associated with increased risks. Further, ideally large-scale multicenter and register-based studies are needed to clarify the role of maternal drug intake for the development of ARM.

Safety and Toxicity of Vitamin A Supplements in Pregnancy

Vitamin A plays an essential role during fetal development; however, if consumed at high doses it can produce teratogenic effects. Synthetic retinoids are potent teratogens and are contraindicated during pregnancy. β-Carotene is free of toxic effects. Intakes of vitamin A less than 10,000 IU per day during pregnancy have not been associated with birth defects. However, there are conflicting results for intakes of 10,000 IU to 30,000 IU per day. Intakes of vitamin A greater than 10,000 IU per day are not recommended for well-nourished pregnant women. Intakes of 30,000 IU per day of vitamin A in nonpregnant women produce only minor increases in the primary teratogen of vitamin A embryopathy. in vitamin A–deficient populations, doses of vitamin A less than 10,000 IU per day or 25,000 IU per week are considered beneficial to pregnant women without risk to the fetus. in these populations, the risks of teratogenicity from high vitamin A intake may need to be balanced against those from a deficiency.

Dietary vitamin A intake below the recommended daily intake during pregnancy and the risk of congenital diaphragmatic hernia in the offspring

BACKGROUND

Vitamin A has been related to the etiology of congenital diaphragmatic hernia (CDH). We performed a case-control study to investigate whether maternal dietary vitamin A intake is related to CDH in the offspring.

METHODS

Thirty-one pregnancies diagnosed with CDH and 46 control pregnancies were included during the study. After CDH diagnosis and inclusion of controls by risk set sampling, maternal vitamin A intake was investigated with a food frequency questionnaire. Serum retinol and retinol-binding protein were determined. Univariable and multivariable logistic regression models were used to calculate risk estimates with adjustment for potential confounders.

RESULTS

We found no significant differences in the overall nutrient and vitamin A intake between case and control mothers. After stratification in body mass index (BMI) categories, case mothers with normal weight showed a lower energy adjusted vitamin A intake (685 vs. 843 μg retinol activity equivalents [RAEs] / day; p = 0.04) and a slightly lower serum retinol (1.58 vs. 1.67 μmol/L; p = 0.08) than control mothers. Vitamin A intake <800 μg retinol activity equivalents (recommended daily intake) in normal weight mothers was associated with a significantly increased CDH risk (odds ratio [OR], 7.2; 95% confidence interval [CI], 1.5-34.4; p = 0.01). Associations were not significantly different in underweight and overweight mothers.

CONCLUSIONS

In normal-weight mothers, dietary vitamin A intake during pregnancy below the recommended daily intake is significantly associated with an increased risk of a child with CDH. This finding supports the retinoid hypothesis in human CDH, but warrants further investigation in larger study populations. Birth Defects Research (Part A), 2013. © 2013 Wiley Periodicals, Inc.

Oral iron prophylaxis in pregnancy: not too little and not too much!

An adequate supply of iron is essential for normal development of the fetus and newborn child. Iron deficiency and iron deficiency anemia (IDA) during pregnancy increase the risk of preterm birth and low birth weight. Iron is important for development of the fetal brain and cognitive abilities of the newborn. Children born to iron-deficient mothers will start their lives suffering from iron deficiency or even IDA. Oral iron prophylaxis to pregnant women improves iron status and prevents development of IDA. The Danish National Board of Health has since 1992 recommended prophylactic oral iron supplements to all pregnant women and the currently advocated dose is 40-50 mg ferrous iron taken between meals from 10 weeks gestation to delivery. However, 30-40 mg ferrous iron is probably an adequate dose in most affluent societies. In developed countries, individual iron prophylaxis guided by iron status (serum ferritin) has physiological advantages compared to general iron prophylaxis. In contrast, in most developing countries, general iron prophylaxis is indicated, and higher doses of oral iron, for example, 60 mg ferrous iron or even more should be recommended, according to the present iron status situation in the specific populations of women of fertile age and pregnant women.

Getting to the heart of the matter: epidemiology of cyanotic heart defects

Congenital heart defects (CHDs) are the most common type of birth defect, making significant contributions to infant morbidity and mortality, but not all CHDs contribute equally to such outcomes. Although cyanotic CHDs constitute some of the most serious CHDs, its epidemiology is poorly understood. We present a comprehensive systematic review of the literature on the epidemiology of cyanotic CHD, with emphasis on the most current knowledge on identified risk/etiologic factors. Literature for this review was identified by searching the PubMed database from the National Center for Biotechnology Information at the US National Library of Medicine as well as bibliographies of identified papers. The 100 reports that contributed to this review describe risk factors such as infant sex, race, and ethnicity, environmental exposures, and maternal and paternal age. Several studies reported differences in prevalence rates by race and ethnicity and elevated sex ratios, and they identified some risk factors, including advanced maternal age. Investigators have made significant progress in the effort to describe the etiology of cyanotic CHDs, but discrepancies, such as the variation in prevalence rates by race and ethnicity and the impact of environmental exposures, still need to be addressed.

Noninherited risk factors and congenital cardiovascular defects: current knowledge: a scientific statement from the American Heart Association Council on Cardiovascular Disease in the Young: endorsed by the American Academy of Pediatrics

Prevention of congenital cardiovascular defects has been hampered by a lack of information about modifiable risk factors for abnormalities in cardiac development. Over the past decade, there have been major breakthroughs in the understanding of inherited causes of congenital heart disease, including the identification of specific genetic abnormalities for some types of malformations. Although relatively less information has been available on noninherited modifiable factors that may have an adverse effect on the fetal heart, there is a growing body of epidemiological literature on this topic. This statement summarizes the currently available literature on potential fetal exposures that might alter risk for cardiovascular defects. Information is summarized for periconceptional multivitamin or folic acid intake, which may reduce the risk of cardiac disease in the fetus, and for additional types of potential exposures that may increase the risk, including maternal illnesses, maternal therapeutic and nontherapeutic drug exposures, environmental exposures, and paternal exposures. Information is highlighted regarding definitive risk factors such as maternal rubella; phenylketonuria; pregestational diabetes; exposure to thalidomide, vitamin A cogeners, or retinoids; and indomethacin tocolysis. Caveats regarding interpretation of possible exposure-outcome relationships from case-control studies are given because this type of study has provided most of the available information. Guidelines for prospective parents that could reduce the likelihood that their child will have a major cardiac malformation are given. Issues related to pregnancy monitoring are discussed. Knowledge gaps and future sources of new information on risk factors are described.

Repeated topical treatment, in contrast to single oral doses, with Vitamin A-containing preparations does not affect plasma concentrations of retinol, retinyl esters or retinoic acids in female subjects of child-bearing age

BACKGROUND

Vitamin A is widely used in cosmetic preparations. Given that oral Vitamin A and its metabolites present a potential reproductive risk, the present study investigated the effect of topical Vitamin A on human endogenous plasma levels of Vitamin A and its metabolites.

METHODS

Two groups of 14 female volunteers of child-bearing age were kept on a Vitamin A-poor diet and treated topically for 21 days with creams containing 0.30% retinol or 0.55% retinyl palmitate on approximately 3000 cm2 of their body surface area, amounting to a total of approximately 30,000 IU Vitamin A/subject/day. After a 12-day wash-out period, the study groups received single oral doses of 10,000 IU or 30,000 IU retinyl palmitate (RP), corresponding to the maximal EU allowance during pregnancy or three-times higher, respectively. Blood samples were collected over 24h on study days -3 (pre-study), 1, 21 (first and last days of topical treatment) and 34 (oral administration) at 0, 1, 2, 4, 6, 8, 12, 14-16 h and 24 h after treatment for determination of plasma concentrations of retinol (REL), retinyl palmitate (RP), oleate (RO) and stearate (RS), 9-cis-, 13-cis-, all-trans- (AT), 13-cis-4-oxo- or AT-4-oxo-retinoic acids (RAs).

RESULTS

With the exception of transient mild (RP-group) to moderate (REL-group) local irritation on the treatment sites, no adverse local or systemic effects were noted. On days 1 or 21 of topical treatment, no changes were measured in individual or group mean plasma Cmax, AUC0-24 h or other pharmacokinetic parameters of REL, retinyl esters or RAs relative to pre-study data. In contrast, single oral doses of RP at 10,000 IU or 30,000 IU produced dose-related and sustained increases in Cmax and AUC0-24 h values of plasma RP, RO, RS, 13-cis- and 13-cis-4-oxo-RAs, as well as a transient increase in AT-RA. In conclusion, our results provide evidence that human topical exposure to retinol- or retinyl ester-containing cosmetic creams at 30,000 IU/day and maximal use concentrations do not affect plasma levels of retinol, retinyl esters or RAs, whereas single oral doses at 10,000 IU or 30,000 IU produce significant increases in plasma retinyl esters and RAs.

Risk and benefit of drug use during pregnancy

Environmental teratogenic factors (e.g. alcohol) are preventable. We focus our analysis on human teratogenic drugs which are not used frequently during pregnancy. The previous human teratogenic studies had serious methodological problems, e.g. the first trimester concept is outdated because environmental teratogens cannot induce congenital abnormalities in the first month of gestation. In addition, teratogens usually cause specific congenital abnormalities or syndromes. Finally, the importance of chemical structures, administrative routes and reasons for treatment at the evaluation of medicinal products was not considered. On the other hand, in the so-called case-control epidemiological studies in general recall bias was not limited. These biases explain that the teratogenic risk of drugs is exaggerated, while the benefit of medicine use during pregnancy is underestimated. Thus, a better balance is needed between the risk and benefit of drug treatments during pregnancy. Of course, we have to do our best to reduce the risk of teratogenic drugs as much as possible, however, it is worth stressing the preventive effect of drugs for maternal diseases (e.g. diabetes mellitus and hyperthermia) related congenital abnormalities.

How useful is the Helen Keller food frequency chart in the determination of the vitamin A status in pregnancy?

Vitamin A deficiency sub clinical or overt, is associated with adverse maternal, fetal and neonatal outcome. This is also true for an excess of vitamin A. The challenge in pregnancy is to detect sub clinical vitamin A deficiency in patients for whom supplements or dietary manipulation will be of benefit. This was a cross sectional case controlled study at the University of Benin Teaching Hospital to compare the Helen Keller Food Frequency Chart with biochemical methods in the determination of vitamin A status in pregnancy. Data was collected from Antenatal patients (142). Using serum Biochemistry three categories of patient were recognized. Patients with normal vitamin A levels (N=100 women with blood vitamin A within two standard deviation of the mean) Twenty-four women (24) had low vitamin A levels (N=24, patients with blood vitamin A level at less than 2 standard deviation below the mean). Eighteen patients (18) had high vitamin A levels (patients with blood vitamin A levels at greater than two standard deviation above the mean). All recruited patients had a dietary assessment using the Helen Keller Food Frequency Chart. The Helen Keller Food Frequency Chart (HKFFC) was found to have a high degree of sensitivity (74.5%) and a high specificity (75%) in detection of patients with vitamin A deficiency. The positive predictive value was 93.62%. The low negative predictive rate of 37.5% however implies that a positive test is more important than a negative test. The HKFFC was unable to differentiate patients with normal or high vitamin A levels. Dietary assessment with the HKFFC is a cheap effective method to detect sub clinical vitamin A deficiency in pregnancy. It is an easy cost effective screening tool to select patients for whom dietary manipulation and or vitamin A supplementation may be beneficial.

Risk of drug-induced congenital defects

Defects attributable to drug therapy represent about 1% of congenital defects of known aetiology. This means that a precautionary attitude and correct use of drugs in fertile, and especially pregnant, women is a feasible form of prevention. Drugs currently in use with proven teratogenic effect number approximately 25, but new pharmaceutical drugs are constantly in preparation. Recognition of a drug-induced teratogenic effect is a complex procedure taking into account not only experimental animal data but also experience in humans. Considering that 40% of pregnancies are not planned, it follows that any drug with known or suspected teratogenic potential must be used only under strict medical control. Also, adequate knowledge on potential teratogenicity of a drug permits modification of therapy before conception. It goes without saying that any drug should be used during pregnancy only if it is essential, and it would be prudent to use only those where adequate information is provided and prior clinical experience is available. Teratology Information Services can assist both physicians and patients when any doubt exists.

Vitamin A and infancy. Biochemical, functional, and clinical aspects

Vitamin A is a very intriguing natural compound. The molecule not only has a complex array of physiological functions, but also represents the precursor of promising and powerful new pharmacological agents. Although several aspects of human retinol metabolism, including absorption and tissue delivery, have been clarified, the type and amounts of vitamin A derivatives that are intracellularly produced remain quite elusive. In addition, their precise function and targets still need to be identified. Retinoic acids, undoubtedly, play a major role in explaining activities of retinol, but, recently, a large number of physiological functions have been attributed to different retinoids and to vitamin A itself. One of the primary roles this vitamin plays is in embryogenesis. Almost all steps in organogenesis are controlled by retinoic acids, thus suggesting that retinol is necessary for proper development of embryonic tissues. These considerations point to the dramatic importance of a sufficient intake of vitamin A and explain the consequences if intake of retinol is deficient. However, hypervitaminosis A also has a number of remarkable negative consequences, which, in same cases, could be fatal. Thus, the use of large doses of retinol in the treatment of some human diseases and the use of megavitamin therapy for certain chronic disorders as well as the growing tendency toward vitamin faddism should alert physicians to the possibility of vitamin overdose.

Effect of co-administration of retinoids on rat embryo development in vitro

BACKGROUND

Excess retinyl palmitate (vitamin A) induces a variety of malformations in many mammalian species, yet retinyl palmitate is not thought to be the proximate teratogen. Many metabolites are generated after oral dosing several of which are, individually teratogenic. It is not known whether these metabolites when present simultaneously interact in an additive or synergistic manner.

METHODS

Whole rat embryos were cultured with retinol, all-trans retinoic acid (tRA), 4-oxo all-trans retinoic acid (4otRA) or 9-cis retinoic acid (9cRA). Retinoids were added singly or in paired combinations at the start of culture and embryos were examined for evidence of dysmorphogenesis at the end of culture. Retinoids were added at both subthreshold and supra-threshold concentrations.

RESULTS

Co-administration of subthreshold concentrations of tRA and 4otRA, retinol and tRA or 4otRA and 4otRA and 9cRA resulted in a greater frequency of abnormal embryos compared to single administration of each retinoid.

CONCLUSIONS

Knowledge of the way in which retinyl palmitate metabolites interact should refine our ability to predict risk from a potentially teratogenic event e.g., accidental overdose with RP during human pregnancy.

Drug-induced congenital defects: strategies to reduce the incidence

Approximately 1% of congenital anomalies relate to pharmacological exposure and are. in theory, preventable. Prevention consists of controlled administration of drugs known to have teratogenic properties (e.g. retinoids, thalidomide). When possible, prevention could take the form of the use of alternative pharmacological therapies during the pre-conception period for certain specific pathologies, selecting the most appropriate agent for use during pregnancy [e.g. haloperidol or a tricyclic antidepressant instead of lithium; anticonvulsant drug monotherapy in place of multitherapy; propylthiouracil instead of thiamazole (methimazole)], and substitution with the most suitable therapy during pregnancy (e.g. insulin in place of oral antidiabetics; heparin in place of oral anticoagulants; alpha-methyldopa instead of ACE inhibitors). Another strategy is the administration of drugs during pregnancy taking into account the pharmacological effects in relation to the gestation period (e.g. avoidance of chemotherapy during the first trimester, avoidance of nonsteroidal anti-inflammatory drugs in the third trimester, and avoidance of high doses of benzodiazepines in the period imminent to prepartum).

Teratology Information Services in Europe and Their Contribution to the Prevention of Congenital Anomalies

OBJECTIVES

To inform on Teratology Information Services (TIS) in Europe, their history, function and activity in preventing congenital malformations.

CONCLUSIONS

Clinical teratology tries to identify human teratogens. TIS play an important role in public health by providing counsel on known reproductive risks and conducting specific research. This has led to a reduction in unnecessary fears of pregnant women and pregnancy terminations, as well as to better, more appropriate drug selection to treat acute or chronic disease. In addition, TIS units also conduct prospective studies and inform the public and physicians of the possible effects of environmental agents on the developing embryo and fetus.

Vitamin A and cardiac outflow tract defects

To assess the relationship between maternal intake of vitamin A and cardiac outflow tract defects, we examined data from a population-based case-control study among liveborn infants born from 1987 through 1989 to mothers residing in the Baltimore-Washington area. Case infants (126) had a nonsyndromic cardiac outflow tract defect. Control infants (679) did not have birth defects and were a stratified random sample of liveborn infants from the same area. The main exposure was average daily maternal intake of retinol and provitamin A carotenoids from foods and supplements during the year before conception. Compared with an average intake of less than 10,000 IU, retinol intake of 10,000 IU or more from supplements was associated with a ninefold increased risk for transposition of the great arteries (odds ratio = 9.2; 95% confidence interval = 4.0-21.2), but not for outflow tract defects with normally related arteries (odds ratio = 0.8; 95% confidence interval = 0.1-6.6). Similar intakes of carotenoids and dietary retinol were not associated with an increased risk for either type of outflow tract defect.

Risk classification systems for drug use during pregnancy: are they a reliable source of information?

BACKGROUND

In several countries, risk classification systems have been set up to summarise the sparse data on drug safety during pregnancy. However, these have resulted in ambiguous statements that are often difficult to interpret and use with accuracy when counselling patients on drug use in pregnancy.

OBJECTIVES

The objective of this study was to compare and analyse the consistency between and the criteria for risk classification for medications used during pregnancy included in 3 widely used international risk classification systems. All 3 systems use categories based on risk factors to summarise the degree to which available clinical information has ruled out the risk to unborn offspring, balanced against the drug's potential benefit to the patient.

METHODS

Drugs included in the risk classification systems from the US Food and Drug Administration (FDA), the Australian Drug Evaluation Committee (ADEC) and the Swedish Catalogue of Approved Drugs (FASS), were reviewed and compared on basis of the risk factor category to which they had been assigned. Agreement between the systems was calculated as the number of drugs common to all 3 and assigned to the same risk factor category. In addition, evidence on teratogenicity and adverse effects during pregnancy was retrieved using a MEDLINE search (from 1966 up to 1998) for common drugs classified as teratogenic.

RESULTS

Differences in the allocation of drugs to different risk factor categories were found. Risk factor category allocation for 645 drugs classified by the FDA, 446 classified by ADEC and 527 classified by FASS was compared. Only 61 (26%) of the 236 drugs common to all 3 systems were placed in the same risk factor category. Analysis of studies on the safety of common drugs during pregnancy of drugs classified as X by the FDA indicated that the variability in category allocation was not only attributable to the different definitions for the categories, but also depended on how the available scientific literature was handled.

CONCLUSIONS

Differences in category allocation for the same drug can be a source of great confusion among users of the classification systems as well as for those who require information regarding risk for drug use during pregnancy, and may limit the usefulness and reliability of risk classification systems.

Vitamin A teratogenicity and risk assessment in the macaque retinoid model

Studies were performed in the cynomolgus monkey (Macaca fascicularis) to provide risk assessment information on safe dose levels of Vitamin A during human pregnancy. Vitamin A palmitate was orally administered at 7500 IU/kg (2.25 mg/kg) to 80 000 IU/kg (24 mg/kg) body weight during early pregnancy (gestation day [GD] 16-27). The results indicated a dose-related increase in exposure (AUC) to retinyl esters and retinoic acids (RA) (all-trans-RA, all-trans-4-oxo-RA, 13-cis-RA, 13-cis-4-oxo-RA). There was also a dose-related increase in abortion and malformation that affected typical retinoid target tissues in the embryo, including the craniofacial region, heart, and thymus. The NOAEL and LOAEL for structural malformations were 7500 IU/kg and 20 000 IU/kg (6 mg/kg), respectively. A companion study involving oral administration of 13-cis-RA during the same gestational period established the NOAEL for malformations at 0.5 mg/kg/day, which is close to the human therapeutic dose range (0.5 to 1.5 mg/kg/day) associated with retinoid embryopathy. Based on the known similarities in teratogenic susceptibility to 13-cis-RA, the monkey NOAEL for Vitamin A (7500 IU/kg) was used to estimate safe levels of this nutrient in humans applying a safety factor of 10. This approach yielded safe levels of Vitamin A during human pregnancy in the range of approximately 25 000 to 37 000 IU/day.

Retinoids in embryonal development

The key role of vitamin A in embryonal development is reviewed. Special emphasis is given to the physiological action of retinoids, as evident from the retinoid ligand knockout models. Retinoid metabolism in embryonic tissues and teratogenic consequences of retinoid administration at high doses are presented. Physiological and pharmacological actions of retinoids are outlined and explained on the basis of their interactions as ligands of the nuclear retinoid receptors. Immediate target genes and the retinoid response elements of their promoters are summarized. The fundamental role of homeobox genes in embryonal development and the actions of retinoids on their expression are discussed. The similarity of the effects of retinoid ligand knockouts to effects of compound retinoid receptor knockouts on embryogenesis is presented. Although much remains to be clarified, the emerging landscape offers exciting views for future research.