Folic acid supplementation and the occurrence of congenital heart defects, orofacial clefts, multiple births, and miscarriage

Key research findings relative to the question of whether maternal use of folic acid before and during pregnancy reduces the chance that offspring will be born with a congenital heart defect or an orofacial cleft are reviewed in this paper. Observational studies in general support an association between maternal use of multivitamins containing folic acid and a reduction in the occurrence of congenital heart defects and orofacial clefts. Results from one randomized controlled trial (RCT) provide the strongest evidence that multivitamins prevent congenital heart defects, but this RCT did not provide evidence that multivitamins prevent orofacial clefts. In addition, most observational and interventional studies are not designed to detect an independent effect from folic acid. Early studies suggested that periconceptional multivitamin use was associated with an increased occurrence of both miscarriages and multiple births, which has resulted in a great deal of controversy about the safety of folic acid use during pregnancy. We also review reports that were designed to answer these questions with more definitive data. When more substantial evidence about the effect of periconceptional folic acid on the occurrence of congenital heart defects and orofacial clefts is reported, we will have additional support for promoting folic acid intervention programs. All women capable of becoming pregnant should continue to consume 400 mug/d of folic acid in addition to a healthy diet as advised.

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.

A population-based birth defects surveillance system in the People's Republic of China

We describe a unique birth defects surveillance system in the People's Republic of China. The system was instituted in March 1992 as a component of an evaluation of the effectiveness of a public health campaign using periconceptional folic acid supplementation to prevent neural tube defects, and currently surveys birth cohorts of approximately 150 000 infants per year. Local health care providers collect information in the form of detailed written descriptions and photographs of affected infants. The system allows for detection of birth defects at the local level with later definitive classification and coding; however, information is limited to structural anomalies that are visible on physical examination. This birth defects surveillance system provides an extensive database of infants with major and minor external structural anomalies, including the unique feature of a photographic record for most cases. These data can be used for aetiological studies, descriptive epidemiology and identification of unusual trends.

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

BACKGROUND

Folic acid supplements are recommended for women of childbearing age to prevent neural tube defects in their offspring. Results of some studies, however, suggest an increase in multiple births associated with use of vitamin supplements that contain folic acid during pregnancy. Our aim was to assess this association.

METHODS

We used data from a population-based cohort study from which we assessed the occurrence of multiple births in women (n=242015) who had participated in a campaign to prevent neural tube defects with folic acid supplements (400 microg per day) in China. Folic acid use was ascertained before pregnancy outcome was known. We studied the relation between multiple births and any use of folic acid pills before or during early pregnancy; additionally, we investigated mechanisms by which folic acid could potentially affect the occurrence of multiple births by examining pill-taking at three time periods: before ovulation, around the time of fertilisation, and after conception.

FINDINGS

1496 (0.62%) multiple births occurred in a cohort of 242015 women who had registered with the study between October, 1993, and September, 1995, and who had a pregnancy not affected by a birth defect; the rate of multiple births in women who did and did not take folic acid before or during early pregnancy was 0.59% and 0.65%, respectively (rate ratio 0.91; 95% CI 0.82-1.00).

INTERPRETATION

Our findings suggest that consumption of folic acid supplements during pregnancy is not associated with an increased occurrence of multiple births.

Folic acid supplementation and risk for imperforate anus in China

Maternal consumption of folic acid before pregnancy and during early pregnancy is associated with a reduced risk for some birth defects. Whether folic acid can reduce the risk for imperforate anus is unknown. As part of a public health campaign conducted in China from 1993 through 1995, the outcomes of pregnancies of > or =20 weeks' gestation were evaluated among women using folic acid supplements. The women were asked to take one pill containing 400 microg of folic acid (without other vitamins) every day from the time of their premarital examination until the end of their first trimester of pregnancy. Rates of imperforate anus and risk ratios for imperforate anus among the offspring of these women were calculated according to folic acid use. Among the offspring of women who took folic acid and women who did not take folic acid, 20 and 30 infants with imperforate anus were identified, respectively. The rate of imperforate anus was 3.1 per 10,000 among the offspring of women who did not take folic acid and 1.6 per 10,000 among the offspring of women who took folic acid; adjusted for maternal age, the risk ratio was 0.59 (95% confidence interval: 0.33, 1.07). Daily maternal consumption of 400 microg of folic acid before and during early pregnancy may reduce the risk for imperforate anus.

Folic acid supplements during pregnancy and risk of miscarriage

BACKGROUND

Although taking supplements that contain 400 microg of folic acid before and during early pregnancy reduces a woman's risk for having a baby with a neural-tube defect (NTD), the effects of such supplements on other pregnancy outcomes remain unclear. We examined whether the use of such supplements affects the occurrence of miscarriage.

METHODS

Participants were women in China who had taken part in a recent folic acid campaign to prevent NTDs and who had registered in this campaign before they became pregnant for the first time. We examined the risk for miscarriage among women who had confirmed pregnancies and who had or had not taken pills containing only 400 microg of folic acid before and during early pregnancy.

RESULTS

The overall rate of miscarriage was 9.1% (2155/23806). The rates of miscarriage among women who had and had not taken folic acid pills before and during the first trimester were 9.0% and 9.3%, respectively (risk ratio 0.97 [95% CI 0.84-1.12]). The distributions of gestational age at pregnancy diagnosis and at miscarriage were similar for both groups of women.

INTERPRETATION

In this population-based study of a cohort of women whose use of folic acid supplements while pregnant had been previously documented and who had been pregnant for the first time, we found no evidence that daily consumption of 400 microg of folic acid before and during early pregnancy influenced their risk for miscarriage.

[Preventing neural tube defects with periconceptional folic acid supplementation: a population-based intervention program in the China]

OBJECTIVES

To evaluate the effectiveness of periconceptional use of 400 microgram folic acid only on the prevention of neural tube defects (NTDs).

METHOD

As part of a public health campaign in areas of high (North) and low (South) NTDs prevalence in the China during 1993 and 1995, 130 142 pill takers and 117 689 non-pill takers were recruited. Women were asked to begin taking a pill containing only 400 microgram of folic acid daily from the time of their premarital examination until the end of the first trimester of pregnancy. The outcomes of these pregnancies were ascertained through 1996.

RESULTS

We identified 102 NTDs among offspring of pill takers and 173 NTDs among offspring of non-pill takers. The NTDs rate in offspring of non-pill takers was 4.8 per thousand (16/3 318) and 1.0 per thousand (28/28 625) in the south; while the rate in pill takers was 1.0 per thousand (13/13 012) in the north and 0.6 per thousand in the south. The greatest reduction in risk occurred among the fetuses or infants of a subgroup of women in the northern region with periconceptional use who took pills more than 80 percent of the time (reduction in risk, 85 percent as compared with the fetuses or infants of women who registered before their last menstrual period and who took no folic acid; 95 percent confidence interval, 62 to 94 percent). In the southern region the reduction in risk among the fetuses or infants of women with periconceptional use of folic acid was also significant (reduction in risk, 41 percent; 95% confidence interval, 3 to 64 percent).

CONCLUSION

Periconceptional intake of supplements containing only 400 microgram folic acid can reduce the risk for NTDs in areas of high and low NTDs prevalence.

Prevention of neural-tube defects with folic acid in China. China-U.S. Collaborative Project for Neural Tube Defect Prevention

BACKGROUND AND METHODS

Periconceptional administration of folic acid can reduce a woman's risk of having a fetus or infant with a neural-tube defect. As part of a public health campaign conducted from 1993 to 1995 in an area of China with high rates of neural-tube defects (the northern region) and one with low rates (the southern region), we evaluated the outcomes of pregnancy in women who were asked to take a pill containing 400 microg of folic acid alone daily from the time of their premarital examination until the end of their first trimester of pregnancy.

RESULTS

Among the fetuses or infants of 130,142 women who took folic acid at any time before or during pregnancy and 117,689 women who had not taken folic acid, we identified 102 and 173, respectively, with neural-tube defects. Among the fetuses or infants of women who registered before their last menstrual period and who did not take any folic acid, the rates of neural-tube defects were 4.8 per 1000 pregnancies of at least 20 weeks' gestation in the northern region and 1.0 per 1000 in the southern region. Among the fetuses or infants of the women with periconceptional use of folic acid, the rates were 1.0 per 1000 in the northern region and 0.6 per 1000 in the southern region. The greatest reduction in risk occurred among the fetuses or infants of a subgroup of women in the northern region with periconceptional use who took folic acid pills more than 80 percent of the time (reduction in risk, 85 percent as compared with the fetuses or infants of women who registered before their last menstrual period and who took no folic acid; 95 percent confidence interval, 62 to 94 percent) [corrected]. In the southern region the reduction in risk among the fetuses or infants of women with periconceptional use of folic acid was also significant (reduction in risk, 41 percent; 95 percent confidence interval, 3 to 64 percent).

CONCLUSIONS

Periconceptional intake of 400 microg of folic acid daily can reduce the risk of neural-tube defects in areas with high rates of these defects and in areas with low rates.

Elevated rates of severe neural tube defects in a high-prevalence area in northern China

In the northern provinces of China, the birth prevalence rate of neural tube defects (NTDs) is among the highest in the world-at about 6 per 1,000 births in rural areas. A unique population-based birth defects surveillance system in which photographs are taken of infants with selected external birth defects was implemented in two provinces in northern China and two provinces in southern China where NTD rates approximate those in the United States. In the period from March 1992 through December 1993, 660 infants with NTDs were identified by the surveillance project from a birth cohort of 251,567. We compared data from the two surveillance areas in China with data from a low-prevalence area in the United States to determine if the pattern of NTD types differs. Based on birth prevalence rates of NTDs from the Metropolitan Atlanta Congenital Defects Program, the observed to expected ratios for two types of NTDs are markedly increased at 80.8 for craniorachischisis and 25.0 for iniencephaly. Rates of these two NTDs in the southern provinces are increased to a lesser degree with observed to expected ratios of 7.1 for craniorachischisis and 2.7 for iniencephaly. The pattern of NTDs in northern China shows an increase in types that are rare in low-prevalence areas such as metropolitan Atlanta. Increased awareness of varying patterns of NTDs in different populations may have important implications for identifying etiologic and pathogenetic mechanisms of NTDs.

Small mammal differentiation on islands

The reason for the distinctiveness of small mammals on islands has traditionally attracted some imaginative story-telling, usually invoking isolation (as a relict) followed by adaptation and/or random genetic changes. Studies of voles on Orkney, long-tailed field mice on the Hebrides and Shetland, and house mice on the Faroe archipelago show that the main factor in differentiating island races from their mainland ancestors is the chance genetic composition of the founding animals. Subsequent change has necessarily to be based on the genes and frequencies carried by this colonizing group. Probably most post-colonization change is adaptive, although possibly limited in extent both by the initial paucity of variation and by the conservative effect of intragenomic interactions. It is probably helpful to recognize that the 'founder effect' or principle commonly invoked in discussions about evolution on islands involves a founder 'event', followed by founder 'selection'. Island differentiation is not necessarily a precursor to speciation, although the wide occurrence of island endemics suggests that founder effects should not be rejected as a driving force initiating speciation. Notwithstanding, island forms provide a valuable 'laboratory' for testing new genetic combinations, a small proportion of which may prove evolutionarily exciting. Only more empirical studies will uncover their evolutionary importance.

Nuclear energy facilities and cancers

Workers employed in the nuclear energy industry and members of the general public living near nuclear facilities are exposed to low levels of ionising radiation as a result of the routine operation of these facilities. For the purposes of radiological protection, it is assumed that low doses of radiation confer a small increased risk of cancer upon the exposed individual and this is a major consideration in setting dose limits for workers and the general public. Quantitative estimates of radiation risk have been derived from epidemiological studies of groups exposed, on average, to high or moderate doses of radiation (such as the Japanese atomic bomb survivors), and appropriate assumptions are made for the application of such estimates to low dose conditions. There have been claims that the risks of cancer in nuclear industry workers, in their children, and in populations living around nuclear facilities have been grossly underestimated. Substantial evidence is now available from the epidemiological study of these groups. Studies of nuclear industry workforces demonstrate that currently accepted risk estimates are at about the right level, although a positive trend of leukaemia mortality with radiation dose, of a magnitude which is compatible with predictions, can be detected in the most statistically powerful workforce studies. The hypothesis that irradiation of fathers before the conception of their children materially increases the risk of childhood leukaemia has been largely discounted since it is biologically implausible and has found no support in studies using data independent of the study which generated the hypothesis. Increased levels of childhood leukaemia have occurred near certain nuclear facilities in the United Kingdom, but it is most unlikely that these are related to exposure to ionising radiation. Recent evidence suggests that these excesses are caused by a rare response to an infectious agent, which is enhanced under the unusual conditions of population mixing found in these communities. Similar excesses of childhood leukaemia have been found in other communities which have experienced unusual population mixing, but are not near nuclear facilities.

Differential male genetic success determines gene flow in an experimentally manipulated mouse population

Sexual selection arises when genetically different males show heritable differences in reproductive success. Mouse mating behaviour involves both male competition and female choice. In this paper we show that introduced Y-linked DNA markers spread more extensively through a natural population than do genes inherited matrilineally. Differences in mating success between the sexes and among individual males may alter the pattern and rate of gene flow in natural populations. Another interesting possibility is that the success of the introduced Y chromosome may be attributable to so-called 'selfish' traits, such as sex-linked meiotic drive or intra-uterine competition. However, this study provides little unequivocal evidence to support this view. Differential success of introduced versus resident males may have implications for the reintroduction of endangered mammals into residual wild populations.

Life history and bioeconomy of the house mouse

1. More is known about the western European house mouse, Mus (musculus) domesticus than any other non-human mammal. If laboratory and field information is combined, an extremely valuable understanding of the species' bioeconomy could be obtained. 2. The seven stages of mouse life-history are surveyed (up to birth, nest life, sex life, social structure, population statics and stability, senescence, and death), and the interactions between the changing phenotype and the environment are described. 3. These interactions can be used to build up a model of the opportunities and compromises which result in the fitness of individual mice. It is not yet possible to quantify such a model, but this should in principle be achievable.

The changing epidemiology of neural tube defects. United States, 1968-1989

OBJECTIVE

To describe the recent trends and epidemiologic characteristics of neural tube defects in the United States.

RESEARCH DESIGN

Ongoing surveillance data.

SETTING

Two birth defect surveillance systems: the nationwide Birth Defects Monitoring Program and the Metropolitan Atlanta (Ga) Congenital Defects Program for 1970 through 1989 and 1968 through 1989, respectively.

PARTICIPANTS

Between 1970 and 1989, using discharge diagnoses of approximately 1 million live-born and stillborn infants per year, the Birth Defects Monitoring Program identified 15,503 cases of spina bifida and anencephaly. Between 1968 and 1989, using discharge diagnoses and clinical records until age 1 year of 38,000 infants per year, the Metropolitan Atlanta Congenital Defects Program identified 800 cases of spina bifida and anencephaly.

INTERVENTIONS

None.

MEASUREMENTS/MAIN RESULTS

Nationwide, neural tube defect rates have declined from 1.3 per 1000 births in 1970 to 0.6 per 1000 births in 1989. In Atlanta, neural tube defect rates have declined from 2.0 per 1000 births in 1968 to 0.6 per 1000 births in 1989. Several changes in the epidemiologic characteristics of neural tube defects were observed: (1) the proportion of spina bifida cases has increased; (2) the proportion of neural tube defect cases compared with the proportion of other unrelated defects has increased; (3) the race ratio of whites to other races for isolated neural tube defect cases has declined in Atlanta; and (4) the rate of isolated neural tube defects in females has also decreased.

CONCLUSIONS

The declining rates of neural tube defects can be partially explained by increased widespread prenatal diagnostic techniques, strongly suggesting the role of environmental factors in neural tube defects. In particular, the use of multivitamins and folic acid to prevent the occurrence of neural tube defects needs further evaluation. Nevertheless, the changing clinical and epidemiologic characteristics of cases over time points to the etiologic heterogeneity of these conditions.