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American Journal of Epidemiology Advance Access originally published online on May 2, 2007
American Journal of Epidemiology 2007 166(3):304-312; doi:10.1093/aje/kwm078
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American Journal of Epidemiology © The Author 2007. Published by the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org.

ORIGINAL CONTRIBUTIONS

Preconception B-Vitamin and Homocysteine Status, Conception, and Early Pregnancy Loss

Alayne G. Ronnenberg1, Scott A. Venners2, Xiping Xu2, Changzhong Chen3, Lihua Wang4, Wenwei Guang4, Aiqun Huang4 and Xiaobin Wang5,6

1 Department of Nutrition, University of Massachusetts Amherst, Amherst, MA
2 Division of Epidemiology and Biostatistics, School of Public Health, University of Illinois, Chicago, IL
3 Channing Laboratory, Brigham and Women's Hospital, Harvard Medical School, Boston, MA
4 Institute for Biomedicine, Anhui Medical University, Hefei, People's Republic of China
5 Mary Ann and J. Milburn Smith Child Health Research Program, Department of Pediatrics, Feinberg School of Medicine, Northwestern University, Chicago, IL
6 Children's Memorial Hospital and Children's Memorial Research Center, Chicago, IL

Correspondence to Dr. Alayne Ronnenberg, Department of Nutrition, 209 Chenoweth Laboratory, University of Massachusetts, 100 Holdsworth Way, Amherst, MA 01003 (e-mail: ronnenberg{at}comcast.net).

Received for publication April 22, 2004. Accepted for publication February 2, 2007.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Maternal vitamin status contributes to clinical spontaneous abortion, but the role of B-vitamin and homocysteine status in subclinical early pregnancy loss is unknown. Three-hundred sixty-four textile workers from Anqing, China, who conceived at least once during prospective observation (1996–1998), provided daily urine specimens for up to 1 year, and urinary human chorionic gonadatropin was assayed to detect conception and early pregnancy loss. Homocysteine, folate, and vitamins B6 and B12 were measured in preconception plasma. Relative to women in the lowest quartile of vitamin B6, those in the third and fourth quartiles had higher adjusted proportional hazard ratios of conception (hazard ratio (HR) = 2.2, 95% confidence interval (CI): 1.3, 3.4; HR = 1.6, 95% CI: 1.1, 2.3, respectively), and the adjusted odds ratio for early pregnancy loss in conceptive cycles was lower in the fourth quartile (odds ratio = 0.5, 95% CI: 0.3, 1.0). Women with sufficient vitamin B6 had a higher adjusted hazard ratio of conception (HR = 1.4, 95% CI: 1.1, 1.9) and a lower adjusted odds ratio of early pregnancy loss in conceptive cycles (odds ratio = 0.7, 95% CI: 0.4, 1.1) than did women with vitamin B6 deficiency. Poor vitamin B6 status appears to decrease the probability of conception and to contribute to the risk of early pregnancy loss in this population.

China; chorionic gonadatropin; folic acid; homocysteine; nutritional status; pregnancy outcome; vitamin B 6; vitamin B 12

Abbreviations: CI, confidence interval; hCG, human chorionic gonadotropin; HR, hazard ratio; OR, odds ratio; PLP, pyridoxal 5'-phosphate (vitamin B6)


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Several studies indicate that micronutrient deficiencies may be common among some Chinese women (1–4). We previously reported a high prevalence of folate and vitamin B6 deficiencies in a group of young women from Anhui province who were attempting to become pregnant (5). There is growing evidence that maternal micronutrient status contributes to poor pregnancy outcome and pregnancy loss. Poor folate status during pregnancy has been associated with numerous adverse pregnancy outcomes (6, 7), including clinical spontaneous abortion (8–12). Suboptimal vitamin B6 status (11) and elevated plasma concentrations of homocysteine, a marker of poor folate or vitamin B12 status, also have been associated with increased risk of clinical spontaneous abortion (9, 13, 14).

In addition to losses that occur after a pregnancy is clinically recognized, as many as two thirds of losses occur before a woman knows she is pregnant (15, 16). However, no studies to date have examined the role of nutritional status in early pregnancy loss. In the current study, we assessed the associations between preconception B-vitamin and homocysteine status and the risks of conception, early pregnancy loss, and clinical pregnancy in a prospective cohort of young Chinese women. To accurately measure conception and early pregnancy loss, we assayed human chorionic gonadotropin (hCG) in daily urine samples collected from the time a woman stopped using contraception until she became pregnant. We assayed vitamin biomarkers in plasma samples collected at baseline, before women stopped using contraception, to assess micronutrient status during the period when they were attempting to conceive.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 References
 
Study population
This study is part of a large prospective study of reproductive health conducted from 1996 to 1998 in textile mills in Anhui, China. The study protocols were approved by the human subjects committees of the affiliated Chinese institutions and by the Institutional Review Board of the Harvard School of Public Health, and all women provided written informed consent.

A detailed description of the study population and data collection methods has been reported previously (16). Briefly, the eligibility criteria for women were as follows: 1) full-time employment; 2) aged 20–34 years; 3) newly married; and 4) had obtained permission to have a child. All the women were nulliparous. Women were excluded if they were already pregnant before enrollment, had tried unsuccessfully to get pregnant for 1 year or more at any time in the past, or planned to quit/change jobs or move out of the city over the 1-year course of follow-up. None of the women had medical conditions that predisposed them to early pregnancy loss, and the rates of fertility and pregnancy losses in our study population were similar to those in previous studies (15–17).

Of 1,006 newly married women who were screened (more than 90 percent of newly married women employed at the mill), 961 met the eligibility requirements and agreed to enroll. We excluded 386 enrolled women from this analysis because they did not collect daily urine (n = 121), did not begin collecting urine soon after stopping contraception (n = 53), never stopped using contraception (n = 95), became pregnant due to contraceptive failure (n = 78), were lost to follow-up (n = 8), withdrew shortly after enrollment (n = 27), or had inadequate diary data (n = 4). The 386 women excluded for the previous reasons were similar to the remaining enrolled women (16). Of the remaining 575 women, 193 were excluded because they did not have baseline nutritional biomarker data, three because they reported current smoking or alcohol use, and 15 because they never conceived and so were not at risk for pregnancy losses. The current analysis is based on 1,165 menstrual cycles from the remaining 364 women after exclusion of 99 cycles in which there was no intercourse reported in a daily diary. Compared with the 364 women included in this analysis, the 211 women excluded because of missing data on nutrition, smoking, alcohol, or failure to conceive were similar in terms of age, height, weight, and body mass index (weight (kg)/height (m)2) but were more educated (45 percent with a high school education or beyond vs. 30 percent).

Data collection procedures
Women's height and body weight in light clothing were measured to the nearest 0.1 cm and 0.1 kg, respectively. An interviewer administered a baseline questionnaire that collected historical data on reproductive history, sociodemographic characteristics, alcohol use, and environmental and occupational exposures. A follow-up questionnaire was administered trimonthly for women who had not become pregnant and at the end of the first, second, and third trimesters of pregnancy for women who became pregnant. If a woman reported a missed or late period or had early signs/symptoms of pregnancy, she was instructed to have a check-up at the affiliated hospital and to provide a urine sample for hCG assay. Once pregnancy was confirmed, the woman received regular prenatal care, delivery services, and postnatal care and was followed up by staff at the designated hospitals according to standard clinical guidelines.

Beginning with the date that contraceptive use ended, each woman kept a daily diary to record sexual intercourse, vaginal bleeding, medication, and medical conditions. She also collected a daily morning first-urine specimen for hCG assay. Daily diary information and urine specimens were collected for up to 12 months or until a pregnancy was clinically confirmed. The first of two consecutive days of bleeding reported in the daily diary was defined as the first day of a menstrual cycle. Women were monitored during ensuing pregnancies (or up to 1 year after beginning to attempt pregnancy if no pregnancy occurred), and all pregnancy outcomes were recorded.

Major outcomes and method of evaluation
The outcomes in this study were defined as follows.

  1. Conception: a conception detected by urinary hCG assay. To distinguish normal variation from a true hCG rise due to conception and to address missing hCG values, we used Bayesian methods (18, 19) to model daily conception status among all the female subjects, including female controls who were not at risk of conception. We showed that this model was 100 percent sensitive and specific for those cycles in which the conception status was observable; that is, the probability of conception was 0.0 in all control cycles and 1.0 in all cycles with conception leading to clinical pregnancy (refer to "Laboratory assay of urinary hCG") (16).
  2. Clinical pregnancy: any pregnancy that lasted 6 weeks (42 days) or more after the onset of the last menstrual period and was confirmed by hCG assay.
  3. Early pregnancy loss: pregnancy loss detected by urinary hCG assay (refer to definition of conception above) occurring less than 6 weeks (42 days) after the onset of the last menstrual period.

Nutritional analyses
At the time of the initial interview, nonfasting blood samples were collected via venipuncture into 10-ml ethylenediaminetetraacetic acid-treated tubes. The blood was centrifuged, and plasma was obtained and stored at –20°C until shipped on dry ice to the Harvard School of Public Health, where it was stored at –70°C prior to nutritional analyses. Frozen samples were then transported to the Jean Mayer USDA [US Department of Agriculture] Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts, where plasma concentrations of homocysteine, folate, and vitamins B6 and B12 were measured. The total homocysteine concentration in plasma was determined by use of a method described by Araki and Sako (20). Plasma folate and vitamin B12 were determined by radioimmunoassay using a commercially available kit from the BioRad Diagnostics Group (Hercules, California). Plasma vitamin B6 (as pyridoxal 5'-phosphate (PLP)) was measured by the tyrosine decarboxylase apoenzyme method (21).

Plasma vitamin concentrations were compared with published reference values to determine the proportions of women with biochemical evidence of vitamin deficiency, defined as less than 6.8 nmol/liter (3 ng/ml) for folate (22), less than 30 nmol/liter of PLP for vitamin B6 (23), and less than 258 pmol/liter (350 pg/ml) for vitamin B12 (24, 25). There is no standard definition of elevated homocysteine. For these analyses, we defined elevated homocysteine as a plasma concentration of 12.4 µmol/liter or greater, which is consistent with the cutoff used in a previous analysis in this cohort (22).

Laboratory assay of urinary hCG
Urine specimens were stored at –20°C. Urinary hCG levels were analyzed per batch by the immunoradiometric assay developed by O'Connor et al. (26) using a combination of capture antibodies for the hCG free ß subunit and hCG ß core fragment (i.e., B204) and the intact hCG molecule (i.e., B109). This assay is highly sensitive and specific. The lowest hCG concentration detectable by the assay was 0.01 ng per ml (1 mIU = 0.2 ng). The cross-reaction of the assay with either intact luteinizing hormone or the luteinizing hormone-free ß subunit was less than 1 percent. All urine specimens from each woman were analyzed and tested during a single run of the assay. Each urine specimen during the window from –10 to +5 days of a menstrual cycle was assayed in duplicate. Discrepancies of more than threefold between duplicate assays were presumed to result from technical error, and the assay was repeated. For the remainder, the geometric mean of the replicates was used to summarize the results for each sample. Urinary creatinine was measured by the Jaffe reaction described by Husdan and Rapoport (27). All hCG values were normalized to creatinine values to adjust for urine concentration. For reference values, we determined levels of hCG from 67 nonconception cycles of 37 control women who were married but using contraception (n = 4), not married (n = 23), or married but not cohabitating with their husbands (n = 10) (16).

Statistical analysis
We described important epidemiologic characteristics of subjects using means and frequencies. We then grouped plasma concentrations of homocysteine and each B vitamin (B6, B12, and folate) in two ways: 1) ordinal quartiles of equal sample sizes and 2) binary categories of normal and abnormal (refer to definitions of elevated homocysteine and deficient B vitamins in "Nutritional analyses"). We used Cox proportional hazards methods (28) to estimate the hazards of conception and clinical pregnancy 1) in the upper three quartiles of homocysteine and B vitamins relative to the lowest quartile and 2) in normal relative to abnormal binary categories (B vitamins) or abnormal relative to normal binary categories (homocysteine). Because we prospectively observed study women for up to 1 year until they achieved a clinical pregnancy, women who had early pregnancy losses prior to clinical pregnancy remained in our cohort and might have had more than one observed conception. We considered the cycles after early pregnancy losses to be the first cycles of new attempted conceptions. We used robust variance estimates (29) to accommodate nonindependence of hazards in multiple attempted conceptions from the same woman. Parameter estimates were similar when we modeled all attempted conceptions versus only the first observed conception from each woman. There were nine right-censored attempted conceptions in which conception did not occur before the end of follow-up and 17 right-censored clinical pregnancy attempts. Each woman had a maximum of one observed clinical pregnancy, and the time to clinical pregnancy was calculated from the beginning of the first conception attempt. We presented these models with and without adjustment for woman's age, body mass index, history of pregnancy, self-reported stress, working shifts, occupational noise and dust exposures, education, and husband's age, smoking, and alcohol drinking. In addition, adjusted models for each B vitamin included the other two remaining B vitamins.

We next limited our analysis to conception cycles and used logistic regression to investigate the relative odds of early pregnancy losses using the same quartile and binary plasma concentration categories as above for homocysteine and B vitamins. We first examined early pregnancy losses by use of only the first observed conception. We then repeated the analyses using all observed conceptions and estimated standard errors using generalized estimating equations to accommodate correlations in pregnancy losses among conceptions from the same women (30). Each model was analyzed with and without adjustment for the same covariates as used in the proportional hazards models.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 References
 
This report includes 364 women who conceived at least once during prospective observation, had adequate daily diary and hCG data, and for whom preconception vitamin and homocysteine concentrations were available (table 1). This was a young, generally lean cohort of newly married women who had obtained permission to have a baby. Most women had no more than a middle-school education, and nearly all worked rotating shifts. Only about 2 percent of women reported using vitamin supplements of any kind. Although women in this group did not smoke or drink alcohol, 57 percent were exposed to passive smoking, and 42 percent reported moderate to high life stress. Overall, 486 (42 percent) of 1,165 cycles resulted in conception; 139 (29 percent) of the 486 conceptions ended in early pregnancy loss.


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  		TABLE 1. Characteristics of 364 nulliparous female textile workers in Anhui, China, who conceived at least once during prospective observation, 1996–1998

 
In general, B-vitamin deficiencies were common in this cohort. Plasma concentrations of PLP indicative of vitamin B6 deficiency were detected in 23 percent of the women, folate deficiency was observed in 20 percent, 18 percent had biochemical evidence of vitamin B12 deficiency, and 10 percent had elevated homocysteine. Overall, 43 percent of the women were deficient in at least one vitamin, although just 9 percent were deficient in both folate and vitamin B6, 7 percent were deficient in both vitamins B6 and B12, and 5 percent were deficient in folate and vitamin B12. Only 3 percent of women were deficient in all three vitamins. The total homocysteine concentration was significantly inversely correlated with both folate (r = –0.17; p = 0.001) and vitamin B12 (r = –0.14; p = 0.009) and positively correlated with vitamin B6 (r = 0.17; p = 0.001). Significant positive correlations (r = 0.22–0.29; p < 0.001) also were observed among the three vitamins.

Table 2 shows the relative hazards of conception for women within different plasma concentrations of B vitamins and homocysteine. Relative to women in the first quartile of plasma vitamin B6, the relative hazards of conception were higher for women in the third (adjusted hazard ratio (HR) = 2.2, 95 percent confidence interval (CI): 1.3, 3.4) and fourth (adjusted HR = 1.6, 95 percent CI: 1.1, 2.3) quartiles. Women with a normal concentration of plasma vitamin B6 had a higher hazard of conception (adjusted HR = 1.4, 95 percent CI: 1.1, 1.9) than did those with vitamin B6 deficiency.


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  		TABLE 2. Relative hazards of conception by preconception plasma B-vitamin and homocysteine concentrations in 364 nulliparous female textile workers in Anhui, China, who conceived at least once during prospective observation, 1996–1998

 
We assessed the relative odds of early pregnancy loss in conception cycles of women within different plasma concentrations of B vitamins and homocysteine (table 3). Compared with women in the lowest quartile of plasma vitamin B6 (PLP: ≤30.4 nmol/liter), those in the fourth quartile (PLP: ≥46.4 nmol/liter) had lower adjusted relative odds of early pregnancy loss (odds ratio (OR) = 0.5, 95 percent CI: 0.3, 1.0). Relative to those with vitamin B6 deficiency (PLP: <30 nmol/liter), women with normal vitamin B6 status had an adjusted odds of early pregnancy loss of 0.7 (95 percent CI: 0.4, 1.1). Compared with women in the lowest quartile of plasma folate (folate: ≤7.2 nmol/liter), those in the fourth quartile of plasma folate (folate: ≥11.8 nmol/liter) had adjusted relative odds of early pregnancy loss that tended toward being lower (adjusted OR = 0.6, 95 percent CI: 0.3, 1.2).


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  		TABLE 3. Adjusted* relative odds of early pregnancy loss in conceptions by preconception plasma B-vitamin and homocysteine concentrations in 364 nulliparous female textile workers in Anhui, China, who conceived at least once during prospective observation, 1996–1998

 
Table 4 shows that, relative to women in the lowest quartile of vitamin B6 (PLP: ≤30.4 nmol/liter), women in the third (38.3–46.3 nmol/liter: HR = 2.0, 95 percent CI: 1.3, 3.0) and fourth (46.4–89.0 nmol/liter: HR = 1.8, 95 percent CI: 1.2, 2.7) quartiles had higher adjusted hazards of clinical pregnancy. Relative to those with vitamin B6 deficiency (PLP: <30 nmol/liter), women with normal vitamin B6 status had an adjusted hazard ratio of clinical pregnancy of 1.6 (95 percent CI: 1.1, 2.2). Compared with women in the lowest quartile of plasma folate (folate: ≤7.2 nmol/liter), those in the fourth quartile (folate: ≥11.8 nmol/liter) tended to have a higher adjusted relative hazard of clinical pregnancy (adjusted HR = 1.3, 95 percent CI: 0.9, 2.0).


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  		TABLE 4. Relative hazards of clinical pregnancy by preconception plasma B-vitamin and homocysteine concentrations in 364 nulliparous female textile workers in Anhui, China, who conceived at least once during prospective observation, 1996–1998

 
We were unable to assess whether specific combinations of B-vitamin deficiencies were associated with conception, early pregnancy loss, or clinical pregnancy because of our limited sample size. However, we did assess whether multiple deficiencies in general were associated with these outcomes. Being deficient in any one or two vitamins was not significantly associated with conception, early pregnancy loss, or clinical pregnancy. However, compared with women who were not deficient in any of the three vitamins, women who were deficient in all three vitamins (n = 10) had adjusted hazard ratios for conception of 0.3 (95 percent CI: 0.2, 0.5) and for clinical pregnancy of 0.2 (95 percent CI: 0.1, 0.6). We did not have sufficient statistical power to test the odds of early pregnancy loss in those with three vitamin deficiencies relative to those with none.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
References
 
Our study examined the relations between preconception B-vitamin status and conception, early pregnancy loss, and clinical pregnancy in a prospective cohort of young Chinese women who were attempting to become pregnant. We found that higher preconception plasma vitamin B6 concentrations were associated with reduced odds of early pregnancy losses and higher probabilities of achieving conception and clinical pregnancy. In a previous report based on women from this same cohort, we reported that the mean prepregnancy plasma vitamin B6 concentration was significantly lower in women whose pregnancies ended in a clinically recognized spontaneous abortion than in those with livebirths (11). The risk of clinical spontaneous abortion was more than twice as high among women in the lowest vitamin B6 quintile compared with those in the highest. In a subsequent analysis of livebirth outcomes (22), we also found that the risk of preterm birth appeared to be about 50 percent lower among women with adequate prepregnancy vitamin B6 status (OR = 0.5, 95 percent CI: 0.2, 1.1) compared with women whose vitamin B6 status was deficient. Previous studies have also reported associations between maternal vitamin B6 status and pregnancy outcome. In a case-control study, Wouters et al. (14) found lower plasma concentrations of vitamin B6 (46 vs. 51 nmol/liter, p < 0.05) in women with histories of recurrent spontaneous abortion compared with control women. Goddijn-Wessel et al. (13) similarly reported lower plasma vitamin B6 (42 vs. 53 nmol/liter, p < 0.05) among women with placental abruption or infarction compared with control women. Taken in their entirety, these observations suggest that maternal vitamin B6 status may influence reproductive events throughout the entire course of pregnancy, from the time of conception through delivery.

The physiology underlying the relation between low vitamin B6 status and early pregnancy loss is unknown, although several biologically plausible mechanisms are possible. Vitamin B6-dependent coenzymes participate in over 100 reactions involved in the metabolism of amino acids, lipids, nucleic acids, and glycogen (31). Vitamin B6 deficiency has also been associated with impairment of enzymes involved in the structural integrity of arterial walls (32), which could affect implantation and early placental development. Low maternal prepregnancy vitamin B6 status could influence early gestational events through these well-known functional roles of the vitamin. In addition, numerous studies have documented associations between low vitamin B6 status and inflammatory responses (33–36), and inflammation has been linked to early pregnancy loss (37, 38). Although we did not assess biomarkers of inflammation in our study, previous studies in Chinese textile workers have shown that exposure to cotton dust initiates both acute and chronic lung inflammation (39). Work-related inflammatory exposures coupled with low vitamin B6 status may have affected the risk of early pregnancy loss in the female textile workers in our cohort. The potential relation between vitamin B6 and inflammation might also help to explain our unexpected positive correlation between plasma concentrations of vitamin B6 and homocysteine, since vitamin B6 levels appear to be lower in inflammatory states independent of homocysteine levels (34). Additional studies that include an independent marker of inflammation, such as C-reactive protein (34), will be needed, however, to help clarify a potential interrelation among vitamin B6 status, inflammation, and early pregnancy loss.

A strength of the current study was that we collected consecutive daily urine samples throughout the entire study period, which allowed us to assay hCG and accurately detect conception and early pregnancy losses. We also assessed vitamin status using plasma samples collected prior to when women began attempting to become pregnant. A limitation was that we based micronutrient status assessment on a single blood sample taken at enrollment. Because some women continued to use contraception after enrolling, some pregnancy outcomes occurred quite distal to micronutrient status assessment. It is possible, therefore, that the women's nutritional status changed between assessment and pregnancy outcome, leading to potential misclassification. For example, although vitamin supplement use in this rural area of China was very low, health-conscious women still might have been more likely to begin vitamin supplementation when they stopped contraception. Misclassification of micronutrient status might explain why the association of vitamin B6 with the hazard of conception appeared to be nonlinear. Another limitation was that, out of 961 enrolled women, we excluded 597 from this analysis. Compared with the excluded women, those included had similar age, height, weight, and body mass index, but less education. Thus, our sample might not be representative of the entire enrolled cohort.

In conclusion, we found that poor preconception vitamin B6 status was associated with increased risk of early pregnancy loss and reduced probabilities of conception and clinical pregnancy in a prospective cohort of young Chinese women. This study underscores the potential importance of micronutrient status at the time of conception on pregnancy outcome.


   ACKNOWLEDGMENTS
 
This study is supported in part by grants R01 HD32505 and R01 HD41702 from the National Institute of Child Health and Human Development; grants R01 ES08337, P01 ES06198, and R01 ES11682 from the National Institute of Environmental Health Sciences; and grants 20-FY98-0701 and 20-FY02-56 from the US March of Dimes Birth Defects Foundation. S. A. V. was supported by grant K01 ES12052 from the National Institute of Environmental Health Sciences.

Conflict of interest: none declared.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 

  1. Zhang ZW, Qu JB, Moon CS, et al. Nutritional evaluation of women in urban areas in continental China. Tohoku J Exp Med (1997) 182:41–59.[CrossRef][ISI][Medline]
  2. Zhan S, Hu Y, Li L. A correlation study on homocysteine metabolism in pregnant women and neural tube defects in urban and rural areas. (In Chinese). Zhonghua Yu Fang Yi Xue Za Zhi (1997) 31:221–4.[Medline]
  3. Ge KY, Chang SY. Dietary intake of some essential micronutrients in China. Biomed Environ Sci (2001) 14:318–24.[ISI][Medline]
  4. Gao X, Yao M, McCrory MA, et al. Dietary pattern is associated with homocysteine and B vitamin status in an urban Chinese population. J Nutr (2003) 133:3636–42.[Abstract/Free Full Text]
  5. Ronnenberg AG, Goldman MB, Aitken IW, et al. Anemia and deficiencies of folate and vitamin B-6 are common and vary with season in Chinese women of childbearing age. J Nutr (2000) 130:2703–10.[Abstract/Free Full Text]
  6. Scholl TO, Hediger ML, Schall JI, et al. Dietary and serum folate: their influence on the outcome of pregnancy. Am J Clin Nutr (1996) 63:520–5.[Abstract/Free Full Text]
  7. Scholl TO, Johnson WG. Folic acid: influence on the outcome of pregnancy. Am J Clin Nutr (2000) 71(suppl):1295S–303S.[Abstract/Free Full Text]
  8. Nelen WL, Blom HJ, Steegers EA, et al. Hyperhomocysteinemia and recurrent early pregnancy loss: a meta-analysis. Fertil Steril (2000) 74:1196–9.[CrossRef][ISI][Medline]
  9. Nelen WL, Blom HJ, Steegers EA, et al. Homocysteine and folate levels as risk factors for recurrent early pregnancy loss. Obstet Gynecol (2000) 95:519–24.[Abstract/Free Full Text]
  10. Hibbard BM. Folates and the fetus. S Afr Med J (1975) 49:1223–6.[ISI][Medline]
  11. Ronnenberg AG, Goldman MB, Chen D, et al. Preconception folate and vitamin B(6) status and clinical spontaneous abortion in Chinese women. Obstet Gynecol (2002) 100:107–13.[Abstract/Free Full Text]
  12. George L, Mills JL, Johansson AL, et al. Plasma folate levels and risk of spontaneous abortion. JAMA (2002) 288:1867–73.[Abstract/Free Full Text]
  13. Goddijn-Wessel TA, Wouters MG, van de Molen EF, et al. Hyperhomocysteinemia: a risk factor for placental abruption or infarction. Eur J Obstet Gynecol Reprod Biol (1996) 66:23–9.[CrossRef][ISI][Medline]
  14. Wouters MG, Boers GH, Blom HJ, et al. Hyperhomocysteinemia: a risk factor in women with unexplained recurrent early pregnancy loss. Fertil Steril (1993) 60:820–5.[ISI][Medline]
  15. Wilcox AJ, Weinberg CR, O'Connor JF, et al. Incidence of early loss of pregnancy. N Engl J Med (1988) 319:189–94.[Abstract]
  16. Wang X, Chen C, Wang L, et al. Conception, early pregnancy loss, and time to clinical pregnancy: a population-based prospective study. Fertil Steril (2003) 79:577–84.[CrossRef][ISI][Medline]
  17. Zinaman MJ, Clegg ED, Brown CC, et al. Estimates of human fertility and pregnancy loss. Fertil Steril (1996) 65:503–9.[ISI][Medline]
  18. Dunson DB, Zhou H. A. Bayesian model of fecundability and sterility. J Am Stat Assoc (2000) 95:1054–62.[CrossRef][ISI]
  19. Gelman A, Carlin J, Stern H, et al. Bayesian data analysis (1997) London, United Kingdom: Chapman and Hall.
  20. Araki A, Sako Y. Determination of free and total homocysteine in human plasma by high-performance liquid chromatography with fluorescence detection. J Chromatogr (1987) 422:43–52.[ISI][Medline]
  21. Shin YS, Rasshofer R, Friedrich B, et al. Pyridoxal-5'-phosphate determination by a sensitive micromethod in human blood, urine and tissues; its relation to cystathioninuria in neuroblastoma and biliary atresia. Clin Chim Acta (1983) 127:77–85.[CrossRef][ISI][Medline]
  22. Ronnenberg AG, Goldman MB, Chen D, et al. Preconception homocysteine and B vitamin status and birth outcomes in Chinese women. Am J Clin Nutr (2002) 76:1385–91.[Abstract/Free Full Text]
  23. Leklem JE. Vitamin B-6: a status report. J Nutr (1990) 120(suppl 11):1503–7.[Abstract/Free Full Text]
  24. Lindenbaum J, Rosenberg IH, Wilson PW, et al. Prevalence of cobalamin deficiency in the Framingham elderly population. Am J Clin Nutr (1994) 60:2–11.[Abstract/Free Full Text]
  25. Allen LH, Casterline J. Vitamin B-12 deficiency in elderly individuals: diagnosis and requirements. Am J Clin Nutr (1994) 60:12–14.[Free Full Text]
  26. O'Connor JF, Schlatterer JP, Birken S, et al. Development of highly sensitive immunoassays to measure human chorionic gonadotropin, its beta-subunit, and beta core fragment in the urine: application to malignancies. Cancer Res (1988) 48:1361–6.[Abstract/Free Full Text]
  27. Husdan H, Rapoport A. Estimation of creatinine by the Jaffe reaction. A comparison of three methods. Clin Chem (1968) 14:222–38.[Abstract]
  28. Cox DR. Regression models and life tables (with discussion). J R Stat Soc (B) (1972) 34:187–220.
  29. Lin DY, Wei LJ. The robust inference for the proportional hazards model. J Am Stat Assoc (1989) 84:1074–8.[CrossRef][ISI]
  30. Liang KY, Zeger S. Longitudinal data analysis using generalized linear models. Biometrica (1986) 73:13–22.[CrossRef]
  31. Leklem JE, Reynolds RE. Challenges and direction in the search for clinical applications of vitamin B6. In: Current topics in nutrition and disease—Leklem JE, Reynolds RE, eds. (1988) New York, NY: Alan R Liss.
  32. Levene CI, Murray JC. The aetiological role of maternal vitamin-B6 deficiency in the development of atherosclerosis. Lancet (1977) 1:628–30.[CrossRef][ISI][Medline]
  33. Kelly PJ, Kistler JP, Shih VE, et al. Inflammation, homocysteine, and vitamin B6 status after ischemic stroke. Stroke (2004) 35:12–15.[Abstract/Free Full Text]
  34. Friso S, Jacques PF, Wilson PW, et al. Low circulating vitamin B(6) is associated with elevation of the inflammation marker C-reactive protein independently of plasma homocysteine levels. Circulation (2001) 103:2788–91.[Abstract/Free Full Text]
  35. Saibeni S, Cattaneo M, Vecchi M, et al. Low vitamin B(6) plasma levels, a risk factor for thrombosis, in inflammatory bowel disease: role of inflammation and correlation with acute phase reactants. Am J Gastroenterol (2003) 98:112–17.[CrossRef][ISI][Medline]
  36. Chiang EP, Bagley PJ, Selhub J, et al. Abnormal vitamin B(6) status is associated with severity of symptoms in patients with rheumatoid arthritis. Am J Med (2003) 114:283–7.[CrossRef][ISI][Medline]
  37. Thellin O, Heinen E. Pregnancy and the immune system: between tolerance and rejection. Toxicology (2003) 185:179–84.[CrossRef][ISI][Medline]
  38. Kwak JY, Beer AE, Kim SH, et al. Immunopathology of the implantation site utilizing monoclonal antibodies to natural killer cells in women with recurrent pregnancy losses. Am J Reprod Immunol (1999) 41:91–8.[ISI][Medline]
  39. Li D, Zhong YN, Rylander R, et al. Longitudinal study of the health of cotton workers. Occup Environ Med (1995) 52:328–31.[Abstract]

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J.G. Ray, J. Goodman, P.R.A. O'Mahoney, M.M. Mamdani, and D. Jiang
High rate of maternal vitamin B12 deficiency nearly a decade after Canadian folic acid flour fortification
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