Obstetrics & Gynecology:
Impact of Folic Acid Fortification in the United States: Markedly Diminished High Maternal Serum Alpha-Fetoprotein Values
Evans, Mark I. MD*; Llurba, Elisa MD†; Landsberger, Ellen J. MD‡; O’Brien, Joseph E. MD§; Harrison, Harold H. MD¶
From the *Department of Obstetrics and Gynecology, Institute for Genetics and Fetal Medicine, St. Luke′s Roosevelt Hospital Center, Columbia University New York, New York; †Hospital Materno-Infantil Vall d'Hebron, Barcelona, Spain; ‡Institute for Human Nutrition, Columbia University, New York, New York; §Quest Diagnostics Laboratory, Teterboro, New Jersey; and ¶Department of Pathology, University of Arizona, Tucson, Arizona.
Received August 25, 2003. Received in revised form November 17, 2003. Accepted December 4, 2003.
Address reprint requests to: Mark I. Evans, MD, Department of Obstetrics and Gynecology, Institute for Genetics and Fetal Medicine, St. Luke′s Roosevelt Hospital Center, 1000 10th Avenue, Suite 11A, New York, NY 10019; e-mail: firstname.lastname@example.org.
OBJECTIVE: Folic acid fortification of breads and grains was implemented in the United States in 1998 in an attempt to reduce the incidence of neural tube defects. Outcome data from birth registries have shown a 20% drop—less than originally predicted. In this study, we ascertain if the impact of folic acid fortification is better seen at the time of midtrimester prenatal diagnosis by looking at incidence of high maternal serum alpha-fetoprotein (MSAFP) values.
METHODS: Data regarding MSAFP levels in 61,119 patients undergoing maternal serum screening at a large commercial laboratory were categorized by multiples of the median (MoM). The data were compared between 2 groups: before mandatory supplementation in the United States in 1997 and after mandatory supplementation in 2000. High MSAFP values were further categorized as high (2.75–4.00 MoM) or very high (more than 4.00 MoM). Data were analyzed by χ2 analysis.
RESULTS: Comparative data showed a 32% decrease of patients with MoM greater than 2.75 + (2.5% −1.7%). Further categorizations revealed similar decreases.
CONCLUSION: The introduction of folic acid fortification has produced a profound decrease in the number of high MSAFP values, reflective of a decreased incidence of neural tube defects. Our results help to validate the decision to fortify food with folic acid, which represents a highly successful public health policy for primary prevention of birth defects.
LEVEL OF EVIDENCE: II-2
Wide fluctuations in the incidence of neural tube defects (NTDs) in the United States and worldwide have been appreciated for decades. In the 1930s, there was an epidemic of NTDs, and there has since been a gradual decline in incidence even before the implementation of high maternal serum alpha-fetoprotein (MSAFP) screening in the 1970s and 1980s.1–3 During the 1990s, United States data from the Centers for Disease Control showed no significant changes in NTD incidence until after fortification in 1998.
These incidence variations are a function of both genetic background and of nutritional status. Although there was considerable confusion and multiple theories as to the etiology of NTDs including potato blight, infections, and alcohol, a general consensus emerged that NTDs are partially precipitated by functional folic acid deficiencies. These are particularly common in poor diets, especially those lacking in fruits and green leafy vegetables. Beginning in the late 1980s, several European studies were conducted using folic acid supplementation preconceptually and early in pregnancy in an attempt to reduce the recurrence risk of both anencephaly and spina bifida.1 Supplementation was given preconceptually and up to 30 days after conception to women who had previous pregnancies with NTDs. Although supplementation effectively raised serum concentrations through the time that the neural tube closes, there was a reduction in the recurrence risk of such NTDs from about 3% to 1%.1 It became commonplace to suggest folic acid supplementation at 4 mg/d for women who had a previously affected child.
However, the vast majority of NTDs occur in the pregnancies of women with no medical history of such defects. Observational studies, nonrandomized intervention studies, and randomized controlled trials in the past 2 decades were carried out to determine if folic acid taken in the periconceptional period could also effectively reduce the primary incidence of NTDs.2–4 In particular, the Czeizel and Dudas study2 in Hungary showed dramatic reductions in NTD risk with the use of multivitamin supplementation. Pilot studies on primary incidence were more difficult to control and required much larger numbers. The data were always confounded by biases, such as overall health status and likelihood of taking vitamin supplementation. There was always the concern of bias between patients who would pay attention to their health care and who would be willing to take prenatal vitamins versus those who would not. A recent review of the Cochrane database5 of 4 trials involving 6,425 women showed that periconceptional folate supplementation reduced the incidence of NTDs by 72%. There was no increase in miscarriage, ectopic pregnancy, or stillbirth, although there was a nonsignificant trend toward increased incidence of multiple gestation.
While these studies were being conducted, organizations such as the U.S. Public Health Service and the American Public Health Association6 were suggesting that doctors who cared for pregnant patients had an “obligation” to ensure that anyone considering pregnancy be taking folic acid supplements before they actually conceived. By 1998, however, less than 30% of women were following this recommendation.7
In view of the suggestive evidence that folic acid supplementation could reduce the incidence of both recurrences and primary occurrences, in 1996 the U.S. Food and Drug Administration mandated that by January 1998, all breads and grains sold in the United States be fortified with folic acid.8 One study to date has evaluated the efficacy of this program based on the number of children with NTDs at birth and showed a decrease,9 but not the 50–60% decrease predicted by the U.S. Public Health Service in 1992.6 The purpose of this study was to ascertain if the impact of folic acid fortification is more apparent at the time of prenatal diagnosis rather than from birth-certificate data.
MATERIALS AND METHODS
Maternal serum alpha-fetoprotein data from 61,119 patients undergoing screening at a large commercial laboratory were categorized by multiples of the median (MoM). The data were compared between 2 groups: before mandatory supplementation in the United States (in 1997) and after mandatory supplementation (in 2000). High MSAFP values were further categorized as high (2.75–4.00 MoM) or very high (more than 4.00 MoM).
Three-month cohorts of 27,020 pregnancies (first quarter) in 1997 and 34,099 pregnancies in 2000 were used for comparison. A competitive radioimmunoassay technique was used for alpha-fetoprotein assays. Reagents were obtained from Sanofi Diagnostics Pasteur Inc. (Marnes-la-Coquette, France). Values were assessed for the in-house MoM. Alpha-fetoprotein data were reported in international units per milliliter (coefficient of variation 6.6–7.7% for values from 25–147 IU/mL). Alpha-fetoprotein values were adjusted clinically for maternal weight, age, race, and gestational age. All data were stratified by MoM to eliminate variability from interassay variation, though this was minimized by using the same laboratory. Although the clinical laboratory cutoff value for high alpha-fetoprotein is 2.5 MoM, there was better segregation of the data by using the breakdowns of less than 2.75 MoM, 2.75–4.00 MoM, and more than 4 MoM. Individual outcome data were not available. Differences were analyzed by χ2 analysis. (SPSS Inc, Chicago, IL). The study was approved by the St. Luke's Roosevelt Hospital Center Institutional Review Board.
The MoM values were determined by using the standard adjustments of gestational age, maternal weight, race and ethnic groups, diabetes status, and multiple gestation.10–14 Of the 61,119 patients who underwent screening with MSAFP as a constituent, 1,278 patients had values of 2.75 MoM or greater. By comparing data from 1997 with 2000, a significant decrease of patients with MoM of 2.75 or greater was seen (χ2 = 50.8, P < .001). The decrease from 2.55% of the population to 1.77% is 32%. Values of more than 4.00 MoM were decreased from 0.75% to 0.52% (χ2 = 43.3, P < .001) (Table 1, Figure 1).
The relationship between MSAFP and NTDs has been known for more than 3 decades. Routine prenatal screening has been conducted in the United States since the mid-1980s. About 2–10% of the patients with an elevated MSAFP will have a fetus with an NTD or another significant congenital anomaly. The positive predictive value of an MSAFP level between 2.5 and 2.9 MoM for NTDs is about 1.45%, with the predictive value as high as 13.4% if the MSAFP level is above 7 MoM; overall, the risk of having an affected fetus is about 4.5% for an MSAFP value above 2.5 MoM.15 In a low-risk population, MSAFP screening for NTDs can detect 71–75% of all defects.16 Birth prevalence of NTDs in the United States has fallen steadily since the epidemic of the 1930s. During the 1990s, before supplementation, there were no significant changes in incidence nor were there any dramatic changes in prenatal diagnosis. Techniques that could give an alternative explanation, such as ultrasonography, did not change significantly between 1997 and 2000.
In this study, we used high MSAFP values as a surrogate for the likelihood of NTDs. The rationale for the surrogate is that birth-registry data do not include data from prenatal diagnosis and terminations. Our thesis is that the incidence of NTDs and subsequent terminations have decreased because of folic acid fortification, perhaps by more than the 20% decrement reflected in the birth-certificate data.
These data, obtained from Quest Diagnostic's database, reflect results from both urban and suburban populations and are generally reflective of the general population of the United States. The laboratories in the system are distributed all over the United States and resemble the population distribution. However, we did not have access to a state-by-state or county-by-county analysis. Such microanalyses have been done for the Atlanta area by the Centers for Disease Control and Prevention and confirm birth prevalence decreases.9
U.S. birth certificate data have shown a 19% decline in NTD incidence in 2001 compared with 1996, before mandatory fortification was instituted.9 Although these results are positive and statistically significant, the decrease in NTDs was less than the decline predicted on the basis of observational studies.12,13 It had been estimated that if 100 μg/d of folic acid were added to the average daily diet of reproductive-aged women, this fortification would result in a 23% decrease in NTDs. However, recent data14 suggest that fortification of cereal-grain food products in the United States has increased typical folic acid consumption by more than 200 μg/d, approximately twice the 70–130-μg/d increment predicted by the Food and Drug Administration.15,16 The prediction for this level should lead to a 41% reduction in NTDs.12 Another predictive study showed 18% and 35% reductions at 100 μg/d and 200 μg/d, respectively.13 These predictions are close to the decrease in the MSAFP levels found in our study.
Even still, our results and all the U.S. data show less improvement than the Hungarian Center randomized trials. There are many possible reasons for these differences. One of the possible explanations for the discrepancy in findings is that many of these studies collected data from birth certificates. An evaluation of birth-certificate data on birth defects showed that birth data had only a 67–86% sensitivity to detect anencephaly and 40% for spina bifida.17,18 Moreover, about 71% of women carrying a fetus with these defects decide to terminate their pregnancy,19 and therefore these would be lost in birth-certificate studies. Another limitation is that national birth certificates do not include fetal deaths or stillbirths, which are common occurrences in fetuses with NTDs.20 Therefore, completed data regarding number of fetuses affected with NTDs are difficult to obtain and probably underestimate the overall incidence. This would decrease the apparent impact of folic acid fortification. If all these limitations are taken into account, it is possible that the decrease would be near that initially predicted. A recent study conducted in Canada after the fortification of grain products in 1998 showed a more than 50% reduction in NTDs when data from live births, stillbirths, and terminations of pregnancies were studied.21
However, during the last 10 years, there has been an overall decrease in the incidence of NTDs. This decline began before fortification was mandatory and may be due to several reasons.22 Since the 1980s, there has been an expansion of second-trimester screening programs for Down syndrome and NTDs, together with an overall improvement in ultrasound detection of fetal anomalies.23,24 The increase in prenatal diagnoses results in an increase in terminations, which decreases birth rates of infants with these anomalies. In addition, it can be assumed that some NTDs were primarily prevented in those women who followed the 1992 recommendation for folic acid supplementation by women who are planning to become pregnant.6 All these efforts in prevention and in prenatal diagnosis had already decreased the incidence of NTDs at birth.25 Therefore, the decrease of these defects at birth after fortification has not been as spectacular as was originally predicted.
In a previous study of MSAFP levels from 1991 to 1995,26 we found that 2.66% of women had an alpha-fetoprotein level above 2.5 MoM. In the current study, we found in 1997 that 2.5% of women had a positive screening test result greater than 2.75 MoM. This represents only a 6% decrease in positive screening results between 1991–1995 and 1997, supporting the idea that the decreased incidence in NTD at birth was more likely due to early detection and termination of pregnancies than to supplementation. This study further shows a decreased incidence of elevated MSAFP to 1.7% in 2000, representing a 32% decrease from 1997 and a 36% decrease from 1991 to 1995. This significant decrease in MSAFP likely reflects primary prevention of NTDs through folic acid fortification.
Before mandatory fortification, less than 30% of women were using folic acid supplements with 400 μg/d in the preconceptional period,7 although 70% of them were aware of the preventive role of folic acid.7,27 This low compliance is partially explained by the fact that more that 50% of pregnancies in United States are unplanned. A study conducted in Germany in 1995 concluded that important factors affecting awareness and use of folic acid were socioeconomic status and level of education.28 Mandatory fortification makes uniform primary prevention possible and is not social-class dependent.29 This expands primary prevention to all women of childbearing age.
More studies are required to determine the optimal level of fortification for the U.S. population.30 The daily upper limit of intake set by the Food and Drug Administration is 1 mg.15 However, it has been suggested that between 0.5% and 5% of adults consume more than 1 mg/d of folic acid.31 With high doses of folic acid, there is a risk of masking the diagnosis of pernicious anemia by delaying the recognition of an underlying vitamin B12 or cobalamin deficiency, even beyond the point of irreversible neurologic damage.32
As first-trimester screening with nuchal translucency and serum biochemical markers becomes more common,33 the incidence of anomalies diagnosed in the second trimester will further decrease. The move toward first-trimester screening will accelerate the phenomenon of diminishing incidence of elevated MSAFPs. Therefore, as the incidence decreases, the cost-effectiveness of screening will decrease, and the positive predictive value of second-trimester MSAFP levels will also decrease. We should then consider higher cutoff values of abnormal MSAFPs to decrease the false-positive rate. This will improve cost-effectiveness and alleviate maternal anxiety arising from false-positive results and the subsequent evaluation with possibly unnecessary invasive procedures.
Overall, the introduction of folic acid fortification of breads and grains in the United States has proven to be a profoundly successful public health experiment, achieving a diminution of the rate of screening positive for MSAFP by approximately 32%. Our results are consistent with observational studies of NTDs at birth in our population and help to validate the decision to fortify food with folic acid. This represents the biggest single step in the reduction of birth defects to date.
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