Folic acid supplements during early pregnancy and likelihood of multiple births: a population-based cohort study

Maternal folic acid supplementation and more prominent birth weight gain in twin birth compared with singleton birth: a cross-sectional study in northwest China

OBJECTIVE

To investigate the association of folic acid (FA) supplementation with birth weight, the risk of small for gestational age (SGA) and low birth weight (LBW) in singleton and twin pregnancy.

DESIGN

A population-based cross-sectional survey.

SETTING

Twenty counties and ten districts in Shaanxi Province of northwestern China, 2013.

PARTICIPANTS

28 174 pregnant women with their infants, covering 27 818 single live births and 356 twin live births.

RESULTS

The prevalence of FA supplementation in singletons and twins was 63·9 and 66·3 %. The mean birth weight was 3267 (sd 459·1) g, 2525 (sd 534·0) g and 2494 (sd 539·5) g; the prevalence of SGA was 14·3, 51·4 and 53·4 %; the prevalence of LBW was 3·4, 42·4 and 46·6 % among singleton, twin A and twin B, respectively. Compared with non-users, women with FA supplementation were (β 17·3, 95 % CI 6·1, 28·4; β 166·3, 95 % CI 69·1, 263·5) associated with increased birth weight, lower risk of SGA (OR 0·85, 95 % CI 0·80, 0·92; OR 0·45, 95 % CI 0·30, 0·68) and LBW (OR 0·82, 95 % CI 0·71, 0·95; OR 0·50, 95 % CI 0·33, 0·75) in singletons and twins, and more prominent effects in twins. Moreover, there were significant interactions between FA supplementation and plurality on birth weight, SGA and LBW.

CONCLUSIONS

The present study suggests the association of periconceptional 0·4 mg/d FA supplementation with increased birth weight and reduced risk of SGA and LBW in both singletons and twins, and this association may be more prominent in twins.

Maternal periconceptional body mass index and risk for neural tube defects: results from a large cohort study in China

Background: Case-control studies have consistently suggested an association between pre- or periconceptional maternal obesity and an increased risk for neural tube defects (NTDs). Few studies have examined the association between body mass index (BMI) and NTDs using measured weight and height. We examined this association in a large cohort study in China.Methods: We used data from a large population-based cohort study established to evaluate the effectiveness of folic acid supplementation to prevent NTDs in China. BMI was computed using maternal weight and height measured before pregnancy or during early pregnancy. External birth defects were identified through a unique birth defects surveillance system. We estimated the birth prevalence and prevalence odds ratios (POR) for NTDs by Chinese BMI categories, controlling for potential confounders.Results: Our study population included a total of 194,844 women. We observed significantly elevated risk for spina bifida (adjusted POR = 5.4, 95% CI: 1.3-22.5) among children born to obese compared to normal weight women. Among women who took folic acid supplements, the adjusted POR for spina bifida among obese women was 10.0 (95% CI: 2.3-42.6) compared to pill users who were of normal weight. Borderline significantly elevated risk was observed for anencephaly (adjusted POR = 1.8; 95% CI: 1.0-3.2) among children born to underweight compared to normal weight women.Conclusions: Our findings suggest that maternal periconceptional obesity may be associated with an increased risk for spina bifida. Maternal underweight may be associated with increased risk for anencephaly.

Twinning and major birth defects, National Birth Defects Prevention Study, 1997-2007

BACKGROUND

Twinning has been associated with many types of birth defects, although previous studies have had inconsistent findings. Many studies lack information about potential confounders, particularly use of fertility treatment. Our objective was to assess the association between twinning and birth defects in the National Birth Defects Prevention Study (NBDPS).

METHODS

We used data from the NBDPS, a population-based, case-control study of major birth defects in the USA, to evaluate associations between twinning and birth defects. The study population included mothers of twin and singleton controls (live-born infants without major birth defects), and cases (fetuses or infants with a major birth defect) born October 1997-December 2007. Adjusted ORs and 95% CIs were estimated using multivariable logistic regression stratified by use of fertility treatment. Twin sex-pairing data and a simulation approach were used to estimate the zygosity of twins.

RESULTS

In the unassisted conception stratum, we observed significant positive associations between twinning and 29 of 45 defect groups. The largest effect estimates were observed for multiple ventricular septal defects and cloacal exstrophy. Among mothers reporting any use of fertility treatments, we observed a significant association with twinning for 5 of 25 defect groups, with the largest effect estimates for hypoplastic left heart syndrome and omphalocele. OR estimates in the estimated monozygotic stratum were generally further from the null than in the dizygotic stratum.

CONCLUSIONS

Compared with singletons, a wide range of birth defects are significantly more common among twins. Birth defect risk in twins may be differential by use of fertility treatment.

Folic acid supplementation: what is new? Fetal, obstetric, long-term benefits and risks

The association between folic acid supplementation, prior to conception and/or during pregnancy and pregnancy outcomes, has been the subject of numerous studies. The worldwide recommendation of folic acid is at least 0.4 mg daily for all women of reproductive age, and 4–5 mg in high-risk women. In addition, evidence shows that folic acid supplementation could modulate other adverse pregnancy outcomes, specifically, in pregnancies complicated by seizure disorders, preeclampsia, anemia, fetal growth restriction and autism. This review summarizes the available national and international guidelines, concerning the indications and dosage of folic acid supplementation during pregnancy. In addition, it describes the potential preventive benefits of folic acid supplementation on multiple maternal and fetal outcomes, as well as potential risks.

Use of psychotropic drugs during pregnancy and breast-feeding

OBJECTIVE

To write clinical guidelines for the use of psychotropic drugs during pregnancy and breast-feeding for daily practice in psychiatry, obstetrics and paediatrics.

METHOD

As we wanted a guideline with a high degree of consensus among health professionals treating pregnant women with a psychiatric disease, we asked the Danish Psychiatric Society, the Danish Society of Obstetrics and Gynecology, the Danish Paediatric Society and the Danish Society of Clinical Pharmacology to appoint members for the working group. A comprehensive review of the literature was hereafter conducted.

RESULTS

Sertraline and citalopram are first-line treatment among selective serotonin reuptake inhibitor for depression. It is recommended to use lithium for bipolar disorders if an overall assessment finds an indication for mood-stabilizing treatment during pregnancy. Lamotrigine can be used. Valproate and carbamazepin are contraindicated. Olanzapine, risperidone, quetiapine and clozapine can be used for bipolar disorders and schizophrenia.

CONCLUSION

It is important that health professionals treating fertile women with a psychiatric disease discuss whether psychotropic drugs are needed during pregnancy and how it has to be administered.

Birth weight and adult cardiovascular risk factors using multiple birth status as an instrumental variable in the 1958 British Birth Cohort

BACKGROUND

Birth weight is classified as a risk factor for cardiovascular disease by the World Health Organization, but appropriate preventive interventions remain unclear because the observations have not been confirmed in experiments and appear to be contextually specific.

METHODS

Using 9452 participants of the 1958 British Birth Cohort at age 42years in 2000 (58% follow-up), we examined the credibility of multiple birth status as an instrumental variable (IV) for birth weight and, if appropriate, use it to obtain less confounded estimates of the associations of birth weight with cardiovascular disease risk factors including self-reported height, body mass index and hypertension than conventional regression in 2014.

RESULTS

Multiple birth (203 twins and 6 triplets) was associated with older maternal age, but not with paternal occupation or maternal smoking. Multiple births had lower birth weight-for-gestational age z-score. Multiple birth status was not directly associated with height, BMI or hypertension. Using IV estimates birth weight-for-gestational age z-score was not clearly associated with height (0.99cm, 95% confidence interval (CI) -0.27, 2.25), body mass index (BMI) (0.42kg/m(2), 95% CI -0.17, 1.01) or hypertension (risk ratio 0.82, 95% CI 0.54, 1.23) adjusted for maternal age, with a first-stage F statistic of 145.3 from IV analysis.

CONCLUSIONS

Multiple birth status is a credible IV for obtaining a less confounded estimate of the association of birth weight with height, BMI and blood pressure. Such analysis suggests that birth weight may be spuriously related to height, BMI and blood pressure, and thus not an effective target for intervention.

Periconceptional Multivitamin Supplementation Containing Folic Acid and Sex Ratio at Birth in a Chinese Population: a Prospective Cohort Study

BACKGROUND

To determine whether periconceptional use of multivitamin supplements containing folic acid increases the occurrence of male births in a Chinese population.

METHODS

A prospective cohort study was carried out in 18 counties in four provinces of China. Participants were naturally and voluntarily divided into an intervention group (who took a multivitamin pill containing folic acid, n = 25,418) and a control group (who did not take any multivitamin, n = 26,580). Multivitamin supplements containing folic acid was ascertained before pregnancy. Pregnant women were followed through the first trimester of pregnancy and the outcome of pregnancy (i.e. livebirth, stillbirth, or fetal death; sex at birth) was recorded.

RESULTS

A total of 52,043 pregnancies and 51,998 births were recorded between September 2000 and August 2002. The proportion of males born to women who did and did not take the multivitamin were 54.8% (n = 13,935) and 54.0% (n = 11,483), respectively. The male to female sex ratios at birth among women who did and did not take the multivitamin were 117:100 and 121:100, respectively. The risk ratio was 1.03 [95% confidence interval 0.99, 1.06] after adjusting for confounding factors.

CONCLUSIONS

These findings suggest that periconceptional multivitamin supplementation containing folic acid is not associated with an increased likelihood of male births in a Chinese population. However, these results may have been affected by induced abortion or selective termination of pregnancy, and the findings must therefore be cautiously interpreted.

Women who deliver twins are more likely to smoke and have high frequencies of specific SNPs: Results from a sample of African-American women who delivered preterm, low birth weight babies

OBJECTIVES

We examine if there are genetic and environmental differences between mothers of singleton and multiple pregnancies in a sample of African-American mothers.

METHODS

We focus on genomic areas suggested to increase or decrease the odds of multiple pregnancies. We computed the odds ratio (OR) and the 95% confidence interval (CI) for each SNP unadjusted or adjusted with smoking. SNPs' allelic differences between mothers of multiple pregnancies and singletons were also tested using Fisher's exact test. We considered additive terms for the SNPs' genotypes, smoking, and a multiplicative interaction term of two selected SNPs' genotypes.

RESULTS

We found significant interactions between smoking and SNPs of the CYP19A, MDM4, MTHFR and TP53 genes which correlated with higher odds of twinning. We also found a significant interaction between SNPs at the TP53 (rs8079544) and MTHFR gene (rs4846049), where the interaction between the homozygotes (TT for rs8079544, GG for rs4846049) correlated with lowered odds of multiple pregnancy.

CONCLUSIONS

We provide a mechanistic explanation and preliminary evidence for previous reports that mothers of twins are more likely to have smoked, despite seemingly conflicting evidence for the fertility-reducing effects of nicotine. Nicotine, as an aromatase inhibitor, inhibits estrogen synthesis and may allow for greater production of gonadotropins. While smoking may have deleterious effects on fertility across many genotypes, in women of specific genotypes it may raise their odds of producing twins. TP53 involvement suggests the necessity of future work examining relationships between women who bear multiples and cancer risk.

Neural Tube Defects: The Experience of the Registry of Congenital Malformations of Alsace, France, 1995-2009

Context and Objective: Considering the lack of accurate and up-to-date information available about neural tube defects (NTDs) in France, the purpose of this study was to review clinical and epidemiological data of NTDs and to evaluate the current efficiency of prenatal diagnosis in Alsace (northeastern France). Methods: A population-based retrospective study was performed from data of the Registry of Congenital Malformations of Alsace between 1995 and 2009. Data were analyzed as a whole and according to the anatomical type of the malformation (anencephaly, cephalocele and spina bifida). Statistical analyses were carried out using the Statistical Package for the Social Sciences. Results: 272 NTDs were recorded divided in 113 cases of anencephaly (42%), 35 cases of cephalocele (13%) and 124 cases of spina bifida (45%). The total prevalence at birth of 14/10,000 (95% CI 13-16) was stable throughout the reporting period. A chromosome abnormality was identified in 27 cases (12% of all karyotyped cases). NTDs were prenatally diagnosed by ultrasound in 88% of the cases. The mean age upon prenatal diagnosis slightly declined during the 15-year period, significantly for spina bifida only. The global rate of terminations of pregnancy following prenatal diagnosis was 97% (230/238). Conclusion: This work constitutes a unique population-based study providing accurate and specific up-to-date data from a unique center over a longer period (1995-2009). The most important information concerns the high and stable prevalence, which calls into question the efficiency of the primary prevention by folic acid supplementation and the efficiency of prenatal diagnosis.

Epidemiology of twinning in the National Birth Defects Prevention Study, 1997 to 2007

BACKGROUND

Our objective was to evaluate associations between twinning and maternal demographic factors and periconceptional exposures among infants with and without orofacial clefts.

METHODS

We used data from the National Birth Defects Prevention Study; 228 twins and 8242 singletons without birth defects (controls), and 117 twins and 2859 singletons with orofacial clefts, born 1997 to 2007, were included in the analyses. Because of the occurrence of twinning due to the use of assisted reproductive technologies, logistic regression models were computed to estimate odds ratios and 95% confidence intervals for each exposure, stratified by fertility treatment use. To evaluate factors by zygosity, we used sex-pairing data and a simulation approach to estimate the zygosity of like-sex twin pairs for unassisted conceptions.

RESULTS

Among control mothers who did not use fertility treatments, predictors of twinning included non-Hispanic black maternal race (adjusted odds ratio, 1.6; 95% confidence interval, 1.0-2.4), and tobacco smoking (adjusted odds ratio, 1.6; 95% confidence interval, 1.1-2.4). Among control mothers who used fertility treatments, older maternal age, higher income, and state of residence were associated with twinning. Associations were generally stronger among mothers of dizygotic (estimated) twins than monozygotic (estimated) twins. Results for mothers of infants with isolated orofacial clefts were similar to those of controls.

CONCLUSION

We observed an increased twinning frequency with increasing maternal age, but factors such as maternal race/ethnicity and socioeconomic status may also contribute. Among women receiving fertility treatments, factors associated with twinning suggested a relation with treatment specifics (e.g., treatment type and number of embryos implanted) and availability of insurance coverage.

Preconception care: nutritional risks and interventions

INTRODUCTION

There is increasingly a double burden of under-nutrition and obesity in women of reproductive age. Preconception underweight or overweight, short stature and micronutrient deficiencies all contribute to excess maternal and fetal complications during pregnancy.

METHODS

A systematic review and meta-analysis of the evidence was conducted to ascertain the possible impact of preconception care for adolescents, women and couples of reproductive age on maternal, newborn and child health (MNCH) outcomes. A comprehensive strategy was used to search electronic reference libraries, and both observational and clinical controlled trials were included. Cross-referencing and a separate search strategy for each preconception risk and intervention ensured wider study capture.

RESULTS

Maternal pre-pregnancy weight is a significant factor in the preconception period with underweight contributing to a 32% higher risk of preterm birth, and obesity more than doubling the risk for preeclampsia, gestational diabetes. Overweight women are more likely to undergo a Cesarean delivery, and their newborns have higher chances of being born with a neural tube or congenital heart defect. Among nutrition-specific interventions, preconception folic acid supplementation has the strongest evidence of effect, preventing 69% of recurrent neural tube defects. Multiple micronutrient supplementation shows promise to reduce the rates of congenital anomalies and risk of preeclampsia. Although over 40% of women worldwide are anemic in the preconception period, only one study has shown a risk for low birth weight.

CONCLUSION

All women, but especially those who become pregnant in adolescence or have closely-spaced pregnancies (inter-pregnancy interval less than six months), require nutritional assessment and appropriate intervention in the preconception period with an emphasis on optimizing maternal body mass index and micronutrient reserves. Increasing coverage of nutrition-specific and nutrition-sensitive strategies (such as food fortification; integration of nutrition initiatives with other maternal and child health interventions; and community based platforms) is necessary among adolescent girls and women of reproductive age. The effectiveness of interventions will need to be simultaneously monitored, and form the basis for the development of improved delivery strategies and new nutritional interventions.

Mandatory fortification of flour with folic acid to prevent neural-tube defects

Firm evidence from randomized, controlled trials that maternal periconceptional folic acid reduced the risk of neural-tube defects was published in the early 1990s. Despite promotion of periconceptional folic acid supplement use, no more than 50% of women take them and so mandatory fortification of a staple food has been considered by many countries as an important adjunct to any public-health approach for the prevention of neural-tube defects. Even 15 years after the confirming evidence, some countries have yet to commit to mandatory fortification and, in those that have, there is limited and poorly coordinated monitoring and evaluation of its effectiveness and safety.

Do assisted conception twins have an increased risk for anencephaly?

BACKGROUND

The incidence rates of anterior neural tube defects, anencephaly and encephalocele appear increased among twins compared with singletons. The current study aimed to evaluate whether the etiology of this phenomenon is related to twinning, assisted reproductive technology (ART), or both.

METHODS

The study cohort consisted of parturient women who were referred to our ultrasonography unit between January 1998 and December 2009 due to suspicion of severe fetal abnormality. The study cohort was divided into two subgroups based on mode of conception: spontaneous and ART (including IVF and ICSI). The subgroups were further subdivided into singleton and multiple pregnancies. We also compared pregnancies diagnosed with anencephaly in the study group to all live births in the Department of Obstetrics and Gynecology.

RESULTS

Anencephaly was diagnosed in 43 fetuses out of 1154 (3.7%) pregnancies diagnosed with severe fetal anomaly. Anencephaly was diagnosed in 9 out of 78 twin pregnancies (11.5%); of these, 8 of 45 (17.8%) were ART conceived and 1 of 33 (3%) spontaneously conceived. A significant correlation was found between twinning and anencephaly, with an odds ratio (OR) of 3.4 [confidence interval (CI) = 1.3-8.9, P= 0.011], while no significant correlation was found between ART and anencephaly. A significant correlation was found between anencephaly and the combination of ART conception and twinning (OR of 6.6, CI = 2.8-15.3, P< 0.01). Analyzing the distribution of pregnancies diagnosed with anencephaly in the study group compared with the total number of live births in the department revealed a significant correlation between twinning and anencephaly, with an OR of 11.4 (CI = 4.9-26.5, P< 0.01), with no significant correlation between ART and anencephaly. Among all live births, a significant correlation was found between anencephaly and the combination of ART conception and twinning (OR of 24.6, CI = 11.4-53.2, P< 0.01).

CONCLUSIONS

Our data suggest that twin pregnancies conceived by ART constitute a high-risk group for anencephaly, due to a possible synergistic effect of twinning and ART.

Twin Town in South Brazil: a Nazi's experiment or a genetic founder effect?

Cândido Godói (CG) is a small municipality in South Brazil with approximately 6,000 inhabitants. It is known as the “Twins' Town” due to its high rate of twin births. Recently it was claimed that such high frequency of twinning would be connected to experiments performed by the German Nazi doctor Joseph Mengele. It is known, however, that this town was founded by a small number of families and therefore a genetic founder effect may represent an alternatively explanation for the high twinning prevalence in CG. In this study, we tested specific predictions of the “Nazi's experiment” and of the “founder effect” hypotheses. We surveyed a total of 6,262 baptism records from 1959–2008 in CG catholic churches, and identified 91 twin pairs and one triplet. Contrary to the “Nazi's experiment hypothesis”, there is no spurt in twinning between the years (1964–1968) when Mengele allegedly was in CG (P = 0.482). Moreover, there is no temporal trend for a declining rate of twinning since the 1960s (P = 0.351), and no difference in twinning among CG districts considering two different periods: 1927–1958 and 1959–2008 (P = 0.638). On the other hand, the “founder effect hypothesis” is supported by an isonymy analysis that shows that women who gave birth to twins have a higher inbreeding coefficient when compared to women who never had twins (0.0148, 0.0081, respectively, P = 0.019). In summary, our results show no evidence for the “Nazi's experiment hypothesis” and strongly suggest that the “founder effect hypothesis” is a much more likely alternative for explaining the high prevalence of twinning in CG. If this hypothesis is correct, then this community represents a valuable population where genetic factors linked to twinning may be identified.

Micronutrients and women of reproductive potential: required dietary intake and consequences of dietary deficiency or excess. Part I--Folate, Vitamin B12, Vitamin B6

This two-part review highlights micronutrients for which either public health policy has been established or for which new evidence provides guidance as to recommended intakes during pregnancy. One pivotal micronutrient is folate, the generic name for different forms of a water-soluble vitamin essential for the synthesis of thymidylate and purines and, hence, DNA. For non-pregnant adult women the recommended intake is 400 μg/day dietary folate equivalent. For women capable of becoming pregnant an additional 400 μg/day of synthetic folic acid from supplements or fortified foods is recommended to reduce the risk of neural tube defects (NTD). The average amount of folic acid received through food fortification (grains) in the US is only 128 μg/day, emphasising the need for the supplemental vitamin for women of reproductive age. Vitamin B12 (cobalamin) is a cofactor required for enzyme reactions, including generation of methionine and tetrahydrofolate. B12 is found almost exclusively in foods of animal origin (meats, dairy products); therefore, vegetarians are at greatest risk for dietary vitamin B12 deficiency and should be supplemented. Vitamin B6 is required for many reactions, primarily in amino acid metabolism. Meat, fish and poultry are good dietary sources. Supplementation beyond routine prenatal vitamins is not recommended.

Fortification of Flour with Folic Acid

Background

After randomized, controlled trials established that consumption of folic acid before pregnancy and during the early weeks of gestation reduces the risk of a neural tube defect (NTD)-affected pregnancy, the United States Public Health Service recommended in 1992 that all women capable of becoming pregnant consume 400 μg folic acid daily. In 1998, folic acid fortification of all enriched cereal grain product flour was fully implemented in the United States and Canada.

Objective

To provide guidance on national fortification of wheat and maize flours to prevent 50 to 70% of the estimated 300,000 NTD-affected pregnancies worldwide.

Methods

An expert workgroup reviewed the latest evidence of effectiveness of folic acid flour fortification and the safety of folic acid.

Results

Recent estimates show that in the United States and Canada, the additional intake of about 100 to 150 μg/day of folic acid through food fortification has been effective in reducing the prevalence of NTDs at birth and increasing blood folate concentrations in both countries. Most potential adverse effects associated with folic acid are associated with extra supplement use not mandatory fortification. Fortification of wheat flour has a proven record of prevention in other developed countries. In 2009, 51 countries had regulations written for mandatory wheat flour fortification programs that included folic acid.

Conclusions

NTDs remain an important cause of perinatal mortality and infantile paralysis worldwide. Mandatory fortification of flour with folic acid has proved to be one of the most successful public health interventions in reducing the prevalence of NTD-affected pregnancies. Most developing countries have few, if any, common sources of folic acid, unlike many developed countries, which have folic acid available from ready-to-eat cereals and supplements. Expanding the number of developed and developing countries with folic acid flour fortification has tremendous potential to safely eliminate most folic acid-preventable NTDs.

A cost-effectiveness analysis of folic acid fortification policy in the United States

OBJECTIVE

To quantify the health and economic outcomes associated with changes in folic acid consumption following the fortification of enriched grain products in the USA.

DESIGN

Cost-effectiveness analysis.

SETTING

Annual burden of disease, quality-adjusted life years (QALY) and costs were projected for four steady-state strategies: no fortification, or fortifying with 140, 350 or 700 microg folic acid per 100 g enriched grain. The analysis considered four health outcomes: neural tube defects (NTD), myocardial infarctions (MI), colon cancers and B12 deficiency maskings.

SUBJECTS

The US adult population subgroups defined by age, gender and race/ethnicity, with folate intake distributions from the National Health and Nutrition Examination Surveys (1988-1992 and 1999-2000), and reference sources for disease incidence, utility and economic estimates.

RESULTS

The greatest benefits from fortification were predicted in MI prevention, with 16 862 and 88 172 cases averted per year in steady state for the 140 and 700 microg fortification levels, respectively. These projections were between 6261 and 38 805 for colon cancer and 182 and 1423 for NTD, while 15-820 additional B12 cases were predicted. Compared with no fortification, all post-fortification strategies provided QALY gains and cost savings for all subgroups, with predicted population benefits of 266 649 QALY gained and $3.6 billion saved in the long run by changing the fortification level from 140 microg/100 g enriched grain to 700 microg/100 g.

CONCLUSIONS

The present study indicates that the health and economic gains of folic acid fortification far outweigh the losses for the US population, and that increasing the level of fortification deserves further consideration to maximise net gains.

National Neural Tube Defects Prevention Program in China

Neural tube defects (NTD) are among the most common and devastating birth defects. Annually, in China, between 80,000 and 100,000 pregnancies result in children born with NTD. Northern China has the highest known rate of NTD in the world. Birth defects are becoming the leading cause of infant mortality in the urban and developed areas in China. The results of studies conducted in the early 1990s and early 2000s showed significant geographic and seasonal variations of folate status among Chinese women of childbearing age, with lower serum and red blood cell folate levels in northern China. In the north, 32% to 35% of women had low plasma folate and low red blood cell folate, and folate levels were significantly lower in spring than in fall. Since 1993, Peking University Health Science Center (formerly Beijing Medical University), collaborating with the US Centers for Disease Control and Prevention (CDC), has conducted a large-scale study to evaluate a public health campaign in China among women preparing for marriage in order to determine the effectiveness of daily supplementation of 400 microg of folic acid alone in preventing NTD in both the north and the south of China. The results showed that among the fetuses or infants of the women who took periconceptional folic acid, the reduction in risk of NTD was 85% in the northern region and 40% in the southern region. Daily intake of 400 microg of folic acid may also reduce the risk of nonsyndromic orofacial clefts. We found no evidence that daily consumption of folic acid before and during early pregnancy influenced the risk of miscarriage or twinning. In 2001, the Chinese Ministry of Health and the Chinese Disabled Person Federation released a National Action Plan for Reducing Birth Defects and Disabilities in China for 2002-2010. The Action Plan aims to improve birth outcomes, to reduce infant mortality by reducing the risk of birth defects and disabilities, and to ensure that every baby is born healthy.

Will increasing folic acid in fortified grain products further reduce neural tube defects without causing harm?: consideration of the evidence

To reduce neural tube defects (NTDs), the U.S. Food and Drug Administration (FDA) mandated that by January 1998 all enriched grain products should contain 140 microg of folic acid (FA)/100 g of flour. Groups concerned with optimal prevention of NTDs had argued that the level should be 350 microg/100 g. However, when it appeared that the debate might delay implementation of any fortification, these groups petitioned the FDA to implement fortification at the originally proposed level of 140 microg/100 g, anticipating that the FDA might consider increasing the level at a later time. Mandated FA fortification (FAF) has now been in place in the United States for 9 y. The impact of this important public health intervention on NTD rates, the possible benefit to other disease conditions, and potential harms have been evaluated. As background for a possible request that the FDA consider increasing FAF, evidence bearing on the question of whether an increase can further reduce NTD births without causing harm is reviewed here. The published data indicate that it is appropriate that the FDA conduct or commission a balanced analysis of the evidence by scientists who will act on that evidence to decide this important question.

Dizygotic twinning

The tendency to conceive spontaneous dizygotic (DZ) twins is a complex trait with important contributions from both environmental factors and genetic disposition. Twins are relatively common and occur on average 13 times per 1000 maternities, though the twinning frequency varies over time and geographic location. This variation is mostly attributed to the differences in DZ twinning rate, since the monozygotic twinning rate is relatively constant. DZ twinning is in part under genetic control, with mothers of DZ twins reporting significantly more female family members with DZ twins than mothers of monozygotic twins. Maternal factors such as genetic history, advanced age and increased parity are known to increase the risk of DZ twins. Recent research confirmed that taller mothers and mothers with a high body mass index (30>) are at greater risk of DZ twinning. Seasonality, smoking, oral contraceptive use and folic acid show less convincing associations with twinning. Genetic analysis is beginning to identify genes contributing to the variation in twinning. Mutations in one of these genes (growth differentiation factor 9) are significantly more frequent in mothers of DZ twins. However, the mutations are rare and only account for a small part of the genetic contribution for twinning.

Folic acid metabolism in human subjects revisited: potential implications for proposed mandatory folic acid fortification in the UK

Following an introduction of the importance of folates and the rationale for seeking to estimate fractional folate absorption from foods (especially for countries not having a mandatory folic acid fortification policy), scientific papers covering the mechanisms of folate absorption and initial biotransformation are discussed. There appears (post-1983) to be a consensus that physiological doses of folic acid undergo biotransformation in the absorptive cells of the upper small intestine to 5-methyltetrahydrofolic acid (as happens for all naturally-occurring reduced 1-carbon-substituted folates). This 'validates' short-term experimental protocols assessing 'relative' folate absorption in human subjects that use folic acid as the 'reference' dose. The underlying scientific premise on which this consensus is based is challenged on three grounds: (i) the apparent absence of a 5-methyltetrahydrofolic acid response in the human hepatic portal vein following absorption of folic acid, (ii) the low dihydrofolate reductase activity peculiar to man and (iii) the implications derived from recent stable-isotope studies of folate absorption. It is concluded that the historically accepted case for folic acid being a suitable 'reference folate' for studies of the 'relative absorption' of reduced folates in human subjects is invalid. It is hypothesised that the liver, and not the absorptive cells of the upper small intestine, is the initial site of folic acid metabolism in man and that this may have important implications for its use as a supplement or fortificant since human liver's low capacity for reduction may eventually give rise to saturation, resulting in significant (and potentially deleterious) unmetabolised folic acid entering the systemic circulation.

Folic acid and risk of twinning: a systematic review of the recent literature, July 1994 to July 2006

OBJECTIVE

To assess the evidence of an association between periconceptional folic acid (FA) supplementation or fortification of foods with FA and the risk of twinning, using the Food Standards Australia New Zealand (FSANZ) framework for assessing evidence when substantiating nutrition, health and related claims on foods.

DATA SOURCES

The Cochrane Library Database, MEDLINE, MEDLINE in Process, EMBASE, PubMed National Library of Medicine, and CINAHL were searched to identify systematic reviews and primary intervention and observational studies published from 1 July 1994 to 7 July 2006.

STUDY SELECTION

One prospective and five retrospective cohort studies that assessed the rate of twinning in populations exposed to FA through supplementation, and six retrospective registry-based cohort studies examining twinning rates after fortification of foods with FA.

DATA EXTRACTION

Two reviewers appraised eligible studies and evaluated data independently.

DATA SYNTHESIS

The best maximal risk estimates of twinning after FA supplementation were an adjusted odds ratio (adjOR) of 1.26 (95% CI, 0.91-1.73) for preconceptional supplementation and dizygotic twinning and an adjOR of 1.02 (95% CI, 0.85-1.24) for overall twinning. Data from four FA fortification studies in the United States that allowed for calculation of an annual percentage increase showed a maximal annual increase in twinning rates of 4.6%.

CONCLUSIONS

Overall, under the FSANZ framework, there is possible evidence for a relationship between periconceptional FA intake and increased twinning. To support this tentative relationship, more well designed, long-term follow-up studies are needed in places where fortification with FA has been introduced, focusing on dose-response and obtaining accurate data on infertility treatments.

Impact of folate and homocysteine metabolism on human reproductive health

Folates belong to the vitamin B group and are involved in a large number of biochemical processes, particularly in the metabolism of homocysteine. Dietary or genetically determined folate deficiency leads to mild hyperhomocysteinemia, which has been associated with various pathologies. Molecular mechanisms of homocysteine-induced cellular dysfunction include increased inflammatory cytokine expression, altered nitric oxide bioavailability, induction of oxidative stress, activation of apoptosis and defective methylation. Whereas the involvement of folate metabolism and homocysteine in ageing-related diseases, in several developmental abnormalities and in pregnancy complications has given rise to a large amount of scientific work, the role of these biochemical factors in the earlier stages of mammalian reproduction and the possible preventive effects of folate supplementation on fertility have, until recently, been much less investigated. In the present article, the possible roles of folates and homocysteine in male and female subfertility and related diseases are systematically reviewed, with regard to the epidemiological, pathological, pharmacological and experimental data of the literature from the last 25 years.

Etiology, pathogenesis and prevention of neural tube defects

Spina bifida, anencephaly, and encephalocele are commonly grouped together and termed neural tube defects (NTD). Failure of closure of the neural tube during development results in anencephaly or spina bifida aperta but encephaloceles are possibly post-closure defects. NTD are associated with a number of other central nervous system (CNS) and non-neural malformations. Racial, geographic and seasonal variations seem to affect their incidence. Etiology of NTD is unknown. Most of the non-syndromic NTD are of multifactorial origin. Recent in vitro and in vivo studies have highlighted the molecular mechanisms of neurulation in vertebrates but the morphologic development of human neural tube is poorly understood. A multisite closure theory, extrapolated directly from mouse experiments highlighted the clinical relevance of closure mechanisms to human NTD. Animal models, such as circle tail, curly tail, loop tail, shrm and numerous knockouts provide some insight into the mechanisms of NTD. Also available in the literature are a plethora of chemically induced preclosure and a few post-closure models of NTD, which highlight the fact that CNS malformations are of hetergeneitic nature. No Mendelian pattern of inheritance has been reported. Association with single gene defects, enhanced recurrence risk among siblings, and a higher frequency in twins than in singletons indicate the presence of a strong genetic contribution to the etiology of NTD. Non-availability of families with a significant number of NTD cases makes research into genetic causation of NTD difficult. Case reports and epidemiologic studies have implicated a number of chemicals, widely differing therapeutic drugs, environmental contaminants, pollutants, infectious agents, and solvents. Maternal hyperthermia, use of valproate by epileptic women during pregnancy, deficiency and excess of certain nutrients and chronic maternal diseases (e.g. diabetes mellitus) are reported to cause a manifold increase in the incidence of NTD. A host of suspected teratogens are also available in the literature. The UK and Hungarian studies showed that periconceptional supplementation of women with folate (FA) reduces significantly both the first occurrence and recurrence of NTD in the offspring. This led to mandatory periconceptional FA supplementation in a number of countries. Encouraged by the results of clinical studies, numerous laboratory investigations focused on the genes involved in the FA, vitamin B12 and homocysteine metabolism during neural tube development. As of today no clinical or experimental study has provided unequivocal evidence for a definitive role for any of these genes in the causation of NTD suggesting that a multitude of genes, growth factors and receptors interact in controlling neural tube development by yet unknown mechanisms. Future studies must address issues of gene-gene, gene-nutrient and gene-environment interactions in the pathogenesis of NTD.

Folic acid: a public-health challenge

Despite worldwide public-health campaigns recommending periconceptional daily supplementation of synthetic folic acid to reduce the risk of neural tube defects, many women are not following these recommendations. At the same time, in most European countries no decline in defects has been recorded in recent years. Vulnerable groups are those with a low standard of education, young people, and women with unplanned pregnancies. Furthermore, in most countries without mandatory fortification, the general population is not consuming the recommended 0.4 mg of food folate per day. Voluntary fortification improves the situation, but does not reach all parts of the population. In the USA, Canada, and Chile, mandatory fortification of flour substantially improved folate and homocysteine status, and neural tube defects rates fell by between 31% and 78%. Nevertheless, many countries do not choose mandatory folic acid fortification, in part because expected additional health benefits are not yet scientifically proven in clinical trials, in part because of feared health risks, and because of the issue of freedom of choice. Thus, additional creative public-health approaches need to be developed to prevent neural tube defects and improve the folate status of the general population.

Folate supplementation and twinning in patients with sickle cell disease

Patients with sickle cell disease routinely take folic acid daily as a supplement to maintain effective erythropoiesis. One of the controversial effects of folic acid is its effect on twin gestation rates. In this report, we present our experience in patients with sickle cell disease and twin pregnancy. Our data show that twin pregnancies seem to be associated with folate supplementation.

Use of periconceptional folic acid supplements in Victoria and New South Wales, Australia

OBJECTIVES

To determine the proportion of women who took folate supplementation prior to conception and in the first three months of pregnancy and/or increased folate dietary intake; to determine how folate supplementation varied with socio-demographic factors; and to describe the ways women had seen or heard about folate prior to pregnancy.

METHODS

Two population-based surveys were used: the Victorian Survey of Recent Mothers 2000 and the 2001 NSW Child Health Survey.

RESULTS

Thirty-six per cent of women in Victoria reported taking periconceptional folate supplements compared with 46% in NSW. In Victoria, 8%, and in NSW, 28% of women had increased dietary folate intake. In both surveys younger women, women with less education, less income, of non-English speaking background and women who were not married were less likely to take folate supplements in the recommended period. In Victoria, multiparous women were significantly less likely to take supplements. In NSW, women with an unplanned pregnancy and those living in rural areas were significantly less likely to take periconceptional folate supplements. Fifty-three per cent of women cited a general practitioner or obstetrician as a source of folate information and 45% cited family or friends; both of these sources were significantly associated with periconceptional folate supplementation.

CONCLUSIONS

Less than 50% of women took periconceptional folate supplements. Among socially disadvantaged groups, the proportion was significantly lower.

IMPLICATIONS

Since women are unlikely to achieve adequate folate intake periconceptionally without deliberate action, there remains the need for a multifaceted approach to providing women with information about folate. Future surveys are needed to monitor usage and knowledge.

Comparison of evidence on harms of medical interventions in randomized and nonrandomized studies

BACKGROUND

Information on major harms of medical interventions comes primarily from epidemiologic studies performed after licensing and marketing. Comparison with data from large-scale randomized trials is occasionally feasible. We compared evidence from randomized trials with that from epidemiologic studies to determine whether they give different estimates of risk for important harms of medical interventions.

METHODS

We targeted well-defined, specific harms of various medical interventions for which data were already available from large-scale randomized trials (> 4000 subjects). Nonrandomized studies involving at least 4000 subjects addressing these same harms were retrieved through a search of MEDLINE. We compared the relative risks and absolute risk differences for specific harms in the randomized and nonrandomized studies.

RESULTS

Eligible nonrandomized studies were found for 15 harms for which data were available from randomized trials addressing the same harms. Comparisons of relative risks between the study types were feasible for 13 of the 15 topics, and of absolute risk differences for 8 topics. The estimated increase in relative risk differed more than 2-fold between the randomized and nonrandomized studies for 7 (54%) of the 13 topics; the estimated increase in absolute risk differed more than 2-fold for 5 (62%) of the 8 topics. There was no clear predilection for randomized or nonrandomized studies to estimate greater relative risks, but usually (75% [6/8]) the randomized trials estimated larger absolute excess risks of harm than the nonrandomized studies did.

INTERPRETATION

Nonrandomized studies are often conservative in estimating absolute risks of harms. It would be useful to compare and scrutinize the evidence on harms obtained from both randomized and nonrandomized studies.

Neurulation in the cranial region--normal and abnormal

Cranial neurulation is the embryonic process responsible for formation of the brain primordium. In the mouse embryo, cranial neurulation is a piecemeal process with several initiation sites and two neuropores. Variation in the pattern of cranial neurulation occurs in different mouse strains, and a simpler version of this morphogenetic scheme has been described in human embryos. Exencephaly is more common in females than in males, an unexplained phenomenon seen in both mice and humans. As the cranial neural tube closes, a critical morphogenetic event is the formation of dorsolateral bending points near the neural fold tips, which enables subsequent midline fusion of the neural folds. Many mutant and gene-targeted mouse strains develop cranial neural tube defects, and analysis of the underlying molecular defects identifies several requirements for normal dorsolateral bending. These include a functional actin cytoskeleton, emigration of the cranial neural crest, spatio-temporally regulated apoptosis, and a balance between cell proliferation and the onset of neuronal differentiation. A small number of mouse mutants exhibit craniorachischisis, a combined brain and spine neurulation defect. Recent studies show that disturbance of a single molecular signalling cascade, the planar cell polarity pathway, is implicated in mutants with this defect.

Case for mandatory fortification of food with folate in Australia, for the prevention of neural tube defects

BACKGROUND

Since the publication of randomized controlled trials demonstrating the prevention of neural tube defects (NTDs) with periconceptional folate, several Australian states have promoted an increase in periconceptional use of folic acid supplements. Since 1996, voluntary fortification of food with folate has been allowed in Australia and New Zealand for the purpose of preventing NTDs.

METHODS

For this report, we synthesized published and unpublished data on folic acid supplement use, voluntary fortification, and trends in NTDs.

RESULTS

There has been an increase in the proportion of women (up to 30-40%) taking periconceptional folic acid supplements in Australia, and many foods (mainly breakfast cereals) are fortified. Supplement use is strongly correlated with educational and socioeconomic status; consumption of voluntarily fortified foods is not. There has been a fall in NTDs of about 30% in the non-Aboriginal population, but no change has been seen in the Aboriginal population.

CONCLUSIONS

These data support mandatory fortification of food as a more equitable approach to achieving sufficient folate intake in the periconceptional period for all women in Australia and New Zealand to prevent the majority of NTDs in their offspring. In May 2004, based on these and other considerations, the Australia and New Zealand Food Regulation Ministerial Council agreed that mandatory fortification of food with folate should be considered as a priority.

Impact of misclassification of in vitro fertilisation in studies of folic acid and twinning: modelling using population based Swedish vital records

OBJECTIVE

To determine whether failure to adequately adjust for a reported 40% misclassification of use of in vitro fertilisation (IVF) as reported in a Swedish study could have led to a false finding that folic acid increases dizygotic twinning.

DESIGN

Modelling with population based data.

SETTING

Swedish vital records for 1995-9.

MAIN OUTCOME MEASURES

Rates of twinning calculated according to whether women used IVF to become pregnant. Estimated unadjusted and adjusted odds ratios of the association between use of folic acid and twinning by use of IVF.

RESULTS

In 1995-9, Swedish women who used IVF had an almost 20 times the chance of having twins than women who did not use IVF (rate ratio 19.7, 95% confidence interval 18.7 to 20.6). In the absence of a true effect of folic acid, the use of a 40% misclassified surrogate variable to adjust for use of IVF would have resulted in a false finding that folic acid was associated with a more than twofold increase in twinning.

CONCLUSION

Use of IVF is a strong confounder because it is associated with both use of folic acid and twinning. Even when misclassification of IVF was reduced to 5%, this bias persisted in the adjusted model. Using a 40% misclassified surrogate to adjust for IVF, as reported in the Swedish study, probably led to a false finding that folic acid increased dizygotic twinning.

Effects of Folic Acid Fortification on Twin Gestation Rates

OBJECTIVE

Previous studies have reported an increase in twinning of as much as 40% associated with folic acid-containing supplements, and folic acid fortification of enriched cereal grains was authorized in 1996. The purpose of this study was to investigate whether twinning rates have increased since that time.

METHODS

We used United States birth and fetal death records to calculate twin gestation rates from 1990 through 2000. To eliminate the influence of fertility treatments, our analysis was limited to nulliparous women aged 16-19. We compared time trends in twin gestation rates before and after folic acid fortification in 1996.

RESULTS

A total of 25,065 twin and 3,362,245 singleton pregnancies were included. Twin gestation rates were stable from January 1990 through December 1996, at 7.2 per 1,000, and then began a steady increase, averaging 2.4% (95% confidence interval 0.1-4.2%, P = .006) per year, which continued through 2000 and reached 8.2 per 1,000. This translates to 2 additional twin pregnancies per 10,000 gestations per year. Twin rates continued to increase well beyond 1998, when the maximal fortification effect on folate status had been reached.

CONCLUSION

Although twin gestation rates in women not using fertility treatments increased after food fortification with folic acid, they rose by much less than the 40% rate previously reported; the observed pattern of increase in twin gestation rates is not consistent with a folic acid fortification effect.

LEVEL OF EVIDENCE

II-2.

Folate Supplementation and Twin Pregnancies

BACKGROUND

Women in many countries are advised to increase their folate intake to lower the risk of neural tube defects. For this purpose several countries add folate to the flour. Therefore, it is important to monitor possible adverse effects of this B vitamin. We have assessed the effect of folate on twin pregnancies.

METHODS

We conducted a retrospective, population-register based study of 176,042 women who gave birth from December 1998 through the end of 2001. Use of folate and multivitamin supplements was recorded on the mandatory birth notification form of the Medical Birth Registry of Norway. Pregnancies after in vitro fertilization (IVF) were reported separately.

RESULTS

With adjustment for maternal age and parity, we observed an increased risk of twin pregnancies associated with preconceptional use of folate (odds ratio = 1.59; 95% confidence interval = 1.41-1.78). This association was largely explained by confounding with IVF pregnancies, which were strongly associated both with twin pregnancies and folate use. After exclusion of known IVF pregnancies, and accounting for underreporting of both IVF pregnancies and folate use, the risk was no longer elevated (1.02; 0.85-1.24). Weak associations with twin pregnancies were observed for use of multivitamins and folate during pregnancy, but could be due to increased use of vitamins after a recognized twin pregnancy.

CONCLUSIONS

The association between preconceptional folate use and twin pregnancies was strongly confounded by IVF. After accounting for IVF pregnancies and underreporting, we found no evidence for an association between preconceptional folate supplements and twinning.

An Exploration of Health Effects of Folic Acid in Pregnancy Beyond Reducing Neural Tube Defects

OBJECTIVES

First, to examine the biological basis of why folic acid may have health effects beyond its proven effect of reducing neural tube defects; and second, to explore current controversial policies of folic acid supplementation and food fortification.

METHODS

We searched MEDLINE for English-language papers published from 1991 to 2003, using the key words "folic acid" and "folate." The literature search was restricted to human studies. Of 8986 publications identified, 65 were relevant to the objectives of this paper.

RESULTS

Analysis of the literature revealed that a major mechanism of folic acid in improving infant health may be related to its effect in correcting maternal folate-homocysteine-methylenetetrahydrofolate reductase metabolic defects. Conversely, exposure to high levels of folic acid may have such adverse health effects as increased risk of neurologic disorders in the general population.

CONCLUSIONS

Randomized trials or well-designed prospective cohort studies are needed to assess the effects of folic acid on various pregnancy outcomes. To enable an examination of the association between folic acid and rare outcomes, such as a specific category of birth defects and fetal and neonatal deaths, it is necessary to recruit a large number of pregnant women to participate in such studies.

Food fortification with folic acid and rate of multiple births, 1994-2000

BACKGROUND

Since fortification of cereal grain products with synthetic folic acid (FA) became mandatory in January 1998, women in the United States who have become pregnant have been exposed to a higher level of FA than women who became pregnant previously. Some studies have suggested that increased FA consumption might increase the risk of multiple gestation pregnancies.

METHODS

Women who had a live birth in Kaiser Foundation Health Plan hospitals from January 1, 1994 through December 31, 2000; all multiple births; and the use of ovulation-inducing drugs were ascertained from electronic databases. Medical records of a sample of women with multiple births who did not use ovulation-inducing drugs were reviewed to determine whether they used assisted reproductive technology. Exposure to FA-fortified foods was based on date of delivery.

RESULTS

The rate of multiple births increased from 13.6 to 14.8 per 1000 live births from 1994 through 2000. The percentage of women who had a multiple birth and who filled a prescription for an ovulation-inducing drug in the 12 months before delivery increased from a low of 6.6% in 1994 to a high of 14.9% in 2000. After excluding women using ovulation-inducing drugs, the increased rate of multiple births was no longer observed.

CONCLUSIONS

While the rates of multiple births have increased since FA fortification became mandatory, this increase can be explained by the increased use of ovulation-inducing drugs. Our findings show no relationship between food fortification with FA and the rates of multiple births in this large, managed health care population.

Use of folic acid supplementation and risk for dizygotic twinning

BACKGROUND

An increase in dizygotic twinning rate after folic acid supplementation has previously been described, but in a recent study from China, no such effect was seen.

AIMS

To further investigate the association between use of folic acid supplement and dizygotic twinning.

STUDY DESIGN

Using the Swedish Medical Birth Registry, the rate of dizygotic twinning among infants of women who reported the use of folic acid was studied, taking a number of confounders into consideration. Comparisons were made with all women recorded in the register.

OUTCOME MEASURE

Unlike-sexed twin pairs were used as representatives of dizygotic twinning.

RESULTS

A number of confounders for the association between folic acid use and twinning were identified and taken into consideration. Women who were immigrants (who used less folic acid and had slightly lower twinning rates than women born in Sweden) and women who reported subfertility problems or treatment for subfertility (who had a high use of folic acid and a high twinning rate) were excluded, and adjustment was then made for year of birth, maternal age, parity, and smoking in early pregnancy. Folic acid use and twinning risk increased with maternal age and decreased with parity. Smokers used less folic acid than nonsmokers. Concomitant use of other drugs was no important confounder except for those used at subfertility. The odds ratio (OR) for dizygotic twinning after folic acid supplementation was then 1.71 (95%CI=1.21-2.42) and for the years 2000-2001 even 2.09 (95%CI=1.39-3.12).

CONCLUSION

There is an increase in twinning rate after folic acid supplementation in a Western population which should be taken into consideration when folic acid supplementation or food fortification is recommended.

Periconceptional folic acid/multivitamin supplementation and twin pregnancy

OBJECTIVE

Results of our previous randomized controlled trial suggested an increase of twin pregnancies that was associated with the use of a multivitamin that contained folic acid during the periconceptional period. These findings were confirmed by US and Swedish studies, but not in the Chinese population. The aim of this analysis is to evaluate this possible association in a population-based data set.

STUDY DESIGN

The population-based large control data set of the Hungarian Case-Control Surveillance of Congenital Abnormalities (1980-1996) was evaluated. Control pregnant women were differentiated according to pre- and postconceptional supplementation of folic acid (in general 6 mg), multivitamins that contained 0.1 to 1.0 mg folic acid, folic acid plus multivitamin, and the prevalence of twin pregnancies was compared with the prevalence of twin pregnancies in the women who did not received supplements as referent.

RESULTS

Of 38,151 women, 395 women gave birth to twins. The prevalence of twin births was 0.78% in the unsupplemented group; the rate of twin pregnancies was 1.52% after the preconceptional supplementation (adjusted odds ratio, 1.80; 95% CI, 1.14-2.85). The proportions of twin pregnancies were 1.14%, 1.45%, and 2.00% after the postconceptional folic acid, multivitamin, and folic acid plus multivitamin supplementation, respectively.

CONCLUSION

Our findings suggest that both pre- and postconceptional supplementation of a high dose of folic acid and multivitamins are associated with a slight increase of the incidence of twin pregnancies.

Solution structure of folic acid. Molecular mechanics and NMR investigation

The structure of folic acid in solution was investigated by nuclear magnetic resonance (NMR) and theoretical calculations. Dynamical information and geometrical constraints were obtained by carbon-13 relaxation study, homo-nuclear NOESY spectra and hetero-nuclear 1H-13C NOE experiments. This set of experimental data was used for the molecular mechanics and molecular dynamic calculations. The accuracy of the final structure was established by the R(NMR) factor, which was calculated comparing the experimental NOESY cross-peaks intensities and the corresponding values simulated by using the complete relaxation matrix analysis (CORMA) approach.

Methylenetetrahydrofolate reductase and transcobalamin genetic polymorphisms in human spontaneous abortion: biological and clinical implications

The pathogenesis of human spontaneous abortion involves a complex interaction of several genetic and environmental factors. The firm association between increased homocysteine concentration and neural tube defects (NTD) has led to the hypothesis that high concentrations of homocysteine might be embryotoxic and lead to decreased fetal viability. There are several genetic polymorphisms that are associated with defects in folate- and vitamin B12-dependent homocysteine metabolism. The methylenetetrahydrofolate reductase (MTHFR) 677C>T and 1298A>C polymorphisms cause elevated homocysteine concentration and are associated with an increased risk of NTD. Additionally, low concentration of vitamin B12 (cobalamin) or transcobalamin that delivers vitamin B12 to the cells of the body leads to hyperhomocysteinemia and is associated with NTD. This effect involves the transcobalamin (TC) 776C>G polymorphism. Importantly, the biochemical consequences of these polymorphisms can be modified by folate and vitamin B12 supplementation. In this review, I focus on recent studies on the role of hyperhomocysteinemia-associated polymorphisms in the pathogenesis of human spontaneous abortion and discuss the possibility that periconceptional supplementation with folate and vitamin B12 might lower the incidence of miscarriage in women planning a pregnancy.

Twinning

Twinning has fascinated human beings over the centuries. New technologies and large study groups have led to improved documentation of frequency and complications in twin pregnancies and long-term outcomes. Artificial reproductive technologies have led to a pronounced rise in numbers of dizygotic and monozygotic twins. Although spontaneous dizygotic twinning is clearly associated with increased concentration of follicle-stimulating hormone and ovulation of more than one egg, causes of monozygotic twinning remain illusive. Twin studies are used increasingly to study complex traits and disorders: however, caution is suggested, since twins might not be representative of a typical singleton pregnancy. Monozygotic twinning seems to represent an anomaly in itself, with an increased number of spontaneous abortions and structural congenital anomalies. Both monozygotic and dizygotic twins have growth rates that slow at 30 weeks in utero and might be programmed both developmentally and biochemically earlier in pregnancy to have different responses at birth and after birth compared with singletons.