Comparison of Plasma Concentrations of Mercury, Cadmium, and Arsenic among Women in 2005 and 2012 in a Historically Contaminated Area in China.

Mercury (Hg), cadmium (Cd), and arsenic (As) concentrations in women were measured and compared to evaluate the effects of environmental heavy-metal pollution control on internal exposure levels. In 2005 and 2012, 200 and 182 women, respectively, were enrolled in the study. Demographic and diet information were collected using a questionnaire. Fasting venous blood samples were collected, and plasma concentrations of Hg, Cd, and As were measured using inductive coupled plasma mass spectrometry. The median concentrations (P25-P75) of Hg, Cd, and As decreased from 0.56 (0.46-0.75) ng/mL, 0.14 (0.09-0.21) ng/mL, and 0.83 (0.66-1.09) ng/mL in 2005 to 0.39 (0.19-0.66) ng/mL, 0.09 (0.05-0.13) ng/mL, and 0.48 (0.29-0.72) ng/mL in 2012, respectively. The difference in plasma metal concentrations between measurements in 2005 and 2012 remained statistically significant after we adjusted for confounders. The adjusted ORs were 0.31 (0.16-0.60), 0.24 (0.12-0.48), and 0.25 (0.13-0.50) for Hg, Cd, and As concentrations, respectively, in 2012, relative to those in 2005. The levels of Hg, Cd, and As were 30% to 40% lower in 2012 than in 2005, indicative of lower human internal exposure to these contaminants due to the implementation of environmental pollution control. Engagement with agriculture and high-frequency water product consumption were associated with high Hg levels, and a high frequency of consumption of fresh fruit and eggs was negatively associated with lower levels of Cd in plasma.

Relationship of Methylation within Upper Stream Region of Transcription Starts Site of HOXA5 Gene with Neural Tube Defects.

Objective To investigate the relationship between the methylation level of transcription starts site (TSS) upper stream of homeobox gene and the neural tube defects (NTDs). Methods A case-control study of two stages was designed. In the first stage,10 cases and 8 controls were extracted,in whom Illumina Infinium Human Methylation 450 k genome-wide beadchip was used for the quantification of DNA methylation levels of brain and spinal tissue. In the second stage,differentially methylated region within HOXA5 gene was detected with a larger numbers of samples (52 cases and 23 controls). DNA of brain or spinal tissue was extracted,and Matrix-assisted laser desorption ionization time-of-flight mass spectrometry technique of MassARRAY platform was employed for the validation of differentially methylated region of HOXA5 gene. Results In the first stage,27 CpG sites within TSS region of HOXA5 gene were found to be significantly hyper-methylated in case group compared to control group (P<0.05). In the second stage,a total of 10 CpG sites were analyzable within the differentially methylated region in the first stage. In the NTD case group,spinal bifida subgroup,and anencephaly subgroup,there were 7,6,and 2 sites with significantly higher methylation levels than that of control group (P<0.05). The average methylation level of TSS upper stream region within HOXA5 gene was higher in case group than control group [case group:(31.3±13.9)%,control group:(21.4±9.7)%],and the odds ratio after adjusting gender of fetus and pregnant week was 1.09 (1.03-1.16). Conclusion Hypermethylation within TSS upper stream region of HOXA5 gene in fetus is associated with a higher risk of NTDs.

Prevention of neural tube defects with folic acid: The Chinese experience.

Neural tube defects (NTDs) are a group of congenital malformations of the central nervous system that are caused by the closure failure of the embryonic neural tube by the 28(th) day of conception. Anencephaly and spina bifida are the two major subtypes. Fetuses with anencephaly are often stillborn or electively aborted due to prenatal diagnosis, or they die shortly after birth. Most infants with spina bifida are live-born and, with proper surgical treatment, can survive into adulthood. However, these children often have life-long physical disabilities. China has one of the highest prevalence of NTDs in the world. Inadequate dietary folate intake is believed to be the main cause of the cluster. Unlike many other countries that use staple fortification with folic acid as the public health strategy to prevent NTDs, the Chinese government provides all women who have a rural household registration and who plan to become pregnant with folic acid supplements, free of charge, through a nation-wide program started in 2009. Two to three years after the initiation of the program, the folic acid supplementation rate increased to 85% in the areas of the highest NTD prevalence. The mean plasma folate level of women during early and mid-pregnancy doubled the level before the program was introduced. However, most women began taking folic acid supplements when they knew that they were pregnant. This is too late for the protection of the embryonic neural tube. In a post-program survey of the women who reported folic acid supplementation, less than a quarter of the women began taking supplements prior to pregnancy, indicating that the remaining three quarters of the fetuses remained unprotected during the time of neural tube formation. Therefore, staple food fortification with folic acid should be considered as a priority in the prevention of NTDs.

[Establishment and evaluation of enzyme-linked immunosorbent assay for measuring human IgM autoantibody to folate receptor].

OBJECTIVE: To establish the method of enzyme-linked immunosorbent assay (ELISA) for measuring human IgM autoantibody to folate receptor. METHODS: Folate receptor was extracted and purified from the healthy woman placenta. The protein was coated on 96-well plates with a concentration of 5 ng/Μl. Goat monoclonal antibody was used for detecting antibody. Pooled plasma from healthy donors was used to plot the standard curve and the IgM concentration of pooled plasma was defined as 1. We set up an ELISA procedure to measure human IgM autoantibody to folate receptor. The sensitivity, precision, and stability of the method were evaluated. Further, the folate receptor and bovine folate-binding protein were used as the antigen, respectively, to determine the autoantibody levels in 24 healthy individuals and 20 individuals once gave birth to baby with neural tube defects. RESULTS: The measuring range of the method was from 6.25 × 10⁻4 to 8.00 × 10⁻². The lowest IgM level that can be detected was 3.12 × 10⁻4. The inter-assay coefficients of variations for samples with high, medium, and low IgM levels were 6.61%,3.50%, and 5.12%, respectively. The intra-assay coefficients of variations were 4.54%, 5.49%, and 5.44%, respectively. The stability test results were considered within acceptable limits. The data from folate receptor-ELISA was significantly higher than that from bovine folate binding protein-ELISA, both in the healthy group (t=-11.9, P<0.001) and in the neural tube defect group (t = 7.35, P<0.001). CONCLUSIONS: The folate receptor-ELISA method for measuring human IgM autoantibody to folate receptor was successfully established. The method is sensitive, repeatable, and stable.

[Establishment and evaluation of enzyme-linked immunosorbent assay for measuring human autoantibody IgG to folate receptor].

OBJECTIVE: To establish and evaluate a newly established method of enzyme-linked immunosorbent assay (ELISA) for measuring human autoantibody to folate receptor (FR). METHODS: Folate receptor was extracted and purified from healthy woman placenta tissues. The protein was coated on 96-well plates. Goat monoclonal antibody was used as detecting antibody to set up the indirect ELISA procedure. The sensitivity, precision and linearity of the method were evaluated. Further, the method was compared with the ELISA method with commercialized bovine folate binding protein (FBP) by determining autoantibody levels in 24 individuals. RESULTS: The measuring range of the standard curve was from 6.25 × 10⁻4 to 8 × 10⁻² (the IgG concentration of pooled plasma from healthy donors was defined as 1). The lowest detectable level was 3.13 × 10⁻4. The intra- and inter-assay coefficients of variations were 2.74%-8.07% and 4.16%-8.23%, respectively. Linearity test results were considered within acceptable limits. The data from FBP-ELISA and FR-ELISA were highly correlated (r=0.954, P<0.001); The value from FR-ELISA was higher by 14% than that from FBP-ELISA. CONCLUSION: The ELISA method for measuring human autoantibody IgG to folate receptor was successfully established using human FR as coating protein. The method is sensitive and repeatable and can be used in large-scale population study.

[Infertility rate in married couples of reproductive age in China: a systematic review and meta-analysis].

OBJECTIVE: To estimate the infertility rates and to examine factors that contribute to the variations in infertility rates among studies. METHODS: Wanfang, CQVIP, CNKI, and PubMed Database were searched for infertility relevant population-based prevalence studies between 1980 and 2012. Meta-analysis and meta-regression were used to calculate the pooled size of effect and to identify the sources of variation. RESULTS: A total of 27 articles using data from regional surveys were included in the review. Results showed that the combined prevalence was 5.7% (95% CI: 5.3%-6.1%). Combined prevalence rates of 1-year and 2-year infertility in newly married couples were 12.5% (95% CI: 9.5%-15.4%) and 6.6% (95% CI: 4.9%-8.4%), respectively, while were respectively 6.4% (95% CI: 4.2%-8.6%) and 3.0% (95% CI: 2.6%-3.3%), in women of reproductive age. Results from Meta-regression showed that the prevalence of 2-year infertility was lower than that of 1-year while infertility in regions was seen higher under the poor socioeconomic condition than in the better regions. Infertility in studies using cohort or prospective studies was seen to be higher than in other studies. CONCLUSION: Owing to the inconsistency in determining the numerator and denominator that were used to calculate the prevalence of infertility as well as the inconsistency in criteria used to define the infertility, an agreed definition on infertility needs to be followed, in order to facilitate the comparison among studies.

[Impact of pregnancy terminations before 28 weeks of gestation on the overall prevalence of neural tube defects in two counties of Shanxi province].

OBJECTIVE: To examine the impact of pregnancy termination before 28 weeks of gestation on the overall prevalence of neural tube defects (NTDs). METHODS: Data collected during the period of 2004 and 2010 from a birth defects surveillance system in Pingding county and Taigu county of Shanxi province were used. Number of births≥28 weeks of gestation and number of cases with major birth defects among the births were collected. Terminations of pregnancies before 28 weeks of gestation due to prenatal diagnosis were also collected. The total prevalence of neural tube defects, prevalence before 28 weeks of gestation, and prevalence of ≥28 weeks gestation were calculated using the total number of pregnancies of ≥28 weeks of gestation as denominator. The prevalence data were compared to examine the impact of pregnancy termination on the total prevalence. The proportions of pregnancy terminations before 28 weeks of gestation due to prenatal diagnosis of an NTD against the total number of NTD cases were also calculated. RESULTS: During 2004-2010, 52 366 births were recorded, and 485 NTD cases were ascertained. The overall prevalence of NTDs was 92.6 per 10,000 births, with prevalence of <28 weeks gestation due to pregnancy terminations as 60.9 per 10,000 births, while the prevalence of ≥28 weeks of gestation was 31.7 per 10,000 births. NTD prevalence of ≥28 weeks gestation was 66.0% lower than the total NTD prevalence. In the last two years, the proportion of NTDs ascertained ≥28 weeks gestation accounted for about 40.0% of the total NTD cases. CONCLUSION: A birth-defect-surveillance program that covered only pregnancies≥28 weeks of gestation resulted in a severe underestimation of the total birth prevalence of NTDs, especially for anencephaly. We would recommend that the current national birth defects surveillance system should include pregnancy terminations before 28 weeks of gestation and the calculation of total NTD prevalence should also include these cases into the numerator, so as to better estimate true population NTD prevalence, upon which the related public health policy is based.

Maternal periconceptional consumption of pickled vegetables and risk of neural tube defects in offspring.

BACKGROUND: Maternal exposure to nitrate, nitrite, and N-nitroso compounds from drinking water or diet has been associated with an increased risk of neural tube defects (NTDs) in some studies. Pickled vegetables contain relatively large amounts of nitrite and N-nitroso compounds. We examined the association between maternal periconceptional consumption of pickled vegetables and NTDs in Shanxi Province of northern China. METHODS: Data were derived from a population based case-control study of major external birth defects in four counties of Shanxi Province. Participants included 519 NTDs cases identified between 2003 and 2007 and 694 healthy controls. Exposure information was collected within 1 week after delivery. Multivariable non-conditional Logistic regression model was used to estimate the adjusted odds ratio (OR) controlling for potential confounding variables. RESULTS: The risk of NTDs was positively associated with the frequency of the consumption of pickled vegetables by the mother. Compared with pickled vegetables consumption at < 1 meal/week, the adjusted OR for consumption at 1 - 3, 4 - 6, and > 6 meals/week were 1.3 (95% confidence interval (CI): 1.0, 1.8), 1.9 (1.1, 3.2), and 3.6 (1.9, 6.9), respectively. A protective effect was found for maternal meat consumption at ≥ 1 meal/week (adjusted OR: 0.6, 95%CI: 0.4, 0.7) and egg or milk consumption at ≥ 1 meal/week (adjusted OR: 0.6, 95%CI: 0.4, 0.8). CONCLUSION: Maternal periconceptional consumption of pickled vegetables may increase the risk for NTDs in Shanxi Province.

Cesarean delivery on maternal request and childhood intelligence: a cohort study.

BACKGROUND: Cesarean section births have been steadily increasing over the past decade and have become an epidemic in China. Cesarean delivery on maternal request is a major contributor to this upward trend, and there has been of much concern about its impact on maternal and child health. Most of mothers believe that cesarean delivery on maternal request can improve the child's intelligence, but direct evidence is sparse. In this cohort study, we aimed to directly assess the impact of cesarean delivery on maternal request on childhood intelligence. METHODS: Intelligence quotient (IQ) of 4144 preschool children from 21 cities/counties of Zhejiang and Jiangsu province whose mothers were registered in a population-based perinatal surveillance program during 1993-1996 was assessed with Chinese Wechsler Young Children Scale of Intelligence (C-WYCSI) in 2000. The outcomes were full-scale IQ, verbal IQ, and performance IQ of C-WYCSI. Mode of delivery and covariates were obtained from the surveillance program. We estimated unadjusted and adjusted effects of cesarean delivery on maternal request and assisted vaginal delivery on IQ scores compared with spontaneous vaginal delivery using regression analysis. RESULTS: The mean full-scale, verbal, and performance IQ for all children was 99.3 ± 16.1, 93.6 ± 17.7, and 105.3 ± 14.3. In crude analysis, cesarean delivery on maternal request versus spontaneous vaginal delivery was associated with an increase of 3.9 (95% confidence interval, 0.6 to 7.2) points in full-scale IQ, 4.8 (1.2 to 8.4) points in verbal IQ, and 2.4 (-0.6 to 5.3) points in performance IQ. After adjusting for maternal education, occupation, and IQ, the advantage was reduced to 1.6 (-1.3 to 4.5), 2.3 (-0.8 to 5.5), and 0.6 (-2.0 to 3.3) points for full-scale, verbal, and performance IQ, respectively. Assisted vaginal delivery versus spontaneous vaginal delivery was not associated with IQ scores in any analysis. CONCLUSION: Neither cesarean delivery on maternal request nor assisted vaginal delivery affected children's IQ.

[Extent and relative changes of equities in using the prenatal care services among premature delivery women with different educational levels].

OBJECTIVE: To understand the extent and relative changes of equities in using the prenatal care services among premature delivery women from 4 counties/cities in Jiangsu and Zhejiang provinces, from 1995 to 2000. METHODS: The study population consisted of 97 537 women who delivered singleton live birth of 28 to 41 gestational weeks in 4 counties/cities of Jiangsu and Zhejiang provinces, from 1995 to 2000. The proportions of women with early prenatal visit, of those with at least five prenatal visits and the hospital delivery rates between premature and term delivery groups were calculated. Inequalities in the above indictors by comparing rate difference (RD), rate ratio (RR) and concentration index (CI) among women with different educational levels, were examined. Chi-square and One-way ANOVA were used to compare the differences. RESULTS: The proportions of having received early prenatal among those women with premature delivery in different education levels were 82.89%, 91.06%, 93.96%, 93.11% respectively, which were less than that of those with full term delivery (86.36%, 93.95%, 95.65%, 96.41%, P = 0.008). The proportions of having received early prenatal among the women with high educational levels were higher (RD = -10.05, RR = 0.90, CI = 0.0104) than those with low educational attainment (RD = -10.22, RR = 0.89, CI = 0.0131); The proportions of having received at least five prenatal visits among those women with premature delivery in different education levels were 86.54%, 93.17%, 92.99%, 96.49%, respectively, which were less than those with full term delivery (94.60%, 96.65%, 96.15%, 96.66%, P = 0.005). The proportions of having had at least five prenatal visits among the women with high educational attainment were higher (RD = -2.06, RR = 0.98, CI = 0.0006) than those with lower educational attainment (RD = -9.95, RR = 0.90, CI = 0.0077); The proportions of hospital delivery among the women with full term delivery in different education levels were significantly higher (99.45%, 99.75%, 99.83%, 99.77%) than those with premature deliveries (98.42%, 99.54%, 99.61%, 100.00%, P = 0.005). The proportions of hospital delivery among women with high educational attainment was higher (RD = -0.32, CI = 0.0003) than those with lower educational attainment (RD = -1.58, CI = 0.0013). CONCLUSION: Education related inequities in prenatal care utilization had not been improved among the Chinese women under our study. Inequities were seen in those women with full-term delivery the preterm delivery ones.

[Study on the current status of spontaneous abortion of primigravid women in Jiaxing of Zhejiang province, China].

OBJECTIVE: To study the current status of spontaneous abortion of primigravid women in Jiaxing areas of Zhejiang province of China. METHODS: We analyzed the data from both perinatal healthcare surveillance program and spontaneous abortion, collected in Jiaxing areas by the Institute of Reproductive and Child Health, Peking University. The study population consisted of 14 769 primigravid women (excluding induced abortion, ectopic pregnancy and molar pregnancy as outcomes) attempting to become pregnant who registered between 1993 and 1995. RESULTS: 1454 spontaneous abortion cases were identified, with the spontaneous abortion rate as 9.8% (95%CI: 9.3% - 10.3%). The mean gestational weeks at pregnancy diagnosis were 7.6 ± 2.1 weeks, the mean gestational weeks at miscarriage were (10.1 ± 3.1) weeks and the incidence of first-trimester (≤ 12 weeks) spontaneous abortion was 7.3% (95%CI: 6.8% - 7.7%), accounting for 73.7% of all the spontaneous abortion cases. A peak for risk of miscarriage was around 8 - 13 weeks, accounting for 37.7% of all spontaneous abortion. The observed multiple Cox regression model showed that increased spontaneous abortion rates were observed in women with age at pregnancy ≥ 30, being peasants and with higher education level. CONCLUSION: The spontaneous abortion rate of primigravid women in Jiaxing areas was higher than in other areas of China. The maximum occurrence of spontaneous abortions was during period of 8-13 gestation weeks.

[Analysis on influencing factors for stunting and underweight among children aged 3 - 6 years in 15 counties of Jiangsu and Zhejiang provinces].

OBJECTIVE: To analyze the influencing factors for stunting and underweight among children aged 3 - 6 years in 15 counties of Jiangsu and Zhejiang provinces so as to provide reference for enhancing growth level among preschool children. METHODS: Data was from the 183 295 records of Children Follow-up Study Project carried out by the Institute of Reproductive and Child Heath of Peking University and the records of related perinatal health care surveillance system in rural areas of 15 counties/cities of Jiangsu and Zhejiang provinces. WHO-NCHS standard was used to assess the childhood physical level of growth. Data of children's birth and their mothers' perinatal health were correlated to determine influencing factors for childhood stunting and underweight. RESULTS: The average stunting rate was 7.95% and underweight rate was 1.55%. Sex, birth weight, preterm birth as well as maternal height, maternal BMI at the first prenatal visit, maternal education and occupation were significantly related to childhood stunting and underweight. Birth weight was the most important influencing factor for childhood underweight. For the groups whose birth weights were < 2500 g and ≥ 2500 g, the rates of underweight were 7.77% and 1.46% respectively. Children with low birth weight were at higher risk for underweight (OR = 3.68, 95%CI: 3.11 - 4.37). Maternal height was the most important influencing factor for childhood stunting. For the groups whose mothers' heights were < 155 cm, 155 - 160 cm, 160 - 165 cm and ≥ 165 cm, the stunting rates were 13.01%, 8.76%, 6.21% and 4.14% respectively. Compared with the ≥ 165 cm group, the < 155 cm group was at higher risk for stunting (OR = 3.08, 95%CI: 2.82 - 3.37). CONCLUSION: Birth weight and maternal height were key factors influencing the growth of children. Perinatal health care and the nutrition status of pregnant mothers should be improved to promote the growth level of preschool children.

[Correlation on hemoglobin concentration and the development of cognition among pre-school children].

OBJECTIVE: Our purpose was to evaluate the association between hemoglobin concentration (Hb) and cognitive ability of children at 4 - 6 years of age in 21 counties/cities in China. METHODS: A total number of 7331 children born during 1993 - 1996 were randomly selected from 21 counties or cities in Hebei, Jiangsu and Zhejiang provinces. Hb concentration of children were measured followed by three tests including full-scale, verbal and performance intelligence quotient (IQ) test performed by Chinese-Wechsler Intelligence Scale for Children, one year later. RESULTS: There were a 0.7 point difference in mean verbal scale IQ (P = 0.144) and a 0.9 point difference in both mean performance and full-scale IQ (P = 0.055 and 0.079, respectively) between anemia and non-anemia groups. Compared with children with non-anemia, children with anemia were 1.3-fold more likely to score poorly in verbal IQ and operational IQ (95%CI: 1.1 - 1.6, 1.1 - 1.5, respectively) and 1.4-fold more likely to have had poor scores in full-scale IQ (95%CI: 1.2 - 1.6) after controlled for children's gender, age at intelligence test, region, parity and mother's IQ, education level, occupation. Participants were divided into 5 sub-groups according to Hb concentration of every 20 percentile. Verbal IQ scores of the lowest (Hb < 110 g/L), moderate (117 g/L /= 130 g/L) were 90.6 +/- 18.1, 94.0 +/- 17.6 and 91.0 +/- 16.4, respectively. Performance IQ scores were 102.2 +/- 15.7, 104.6 +/- 14.8 and 100.5 +/- 14.9, respectively. Full-scale IQ scores were 95.9 +/- 17.3, 99.0 +/- 16.4 and 95.2 +/- 15.6, respectively. Children with both low and high hemoglobin levels did poorly in all intelligence tests than children with moderate Hb concentration (P < 0.001). After controlling for confounding factors, children with the lowest concentration were 1.4-fold more likely to have had poor verbal and performance scores than children with moderate Hb concentration (95%CI: 1.1 - 1.7, 1.1 - 1.8, respectively) and 1.5-fold (95%CI: 1.2 - 1.8) more likely to have had poor full-scale scores than those with moderate Hb concentration. The association between high Hb concentration and low IQ scores disappeared in the multivariate model. CONCLUSION: Low Hb concentration might have adversely affected children's cognitive development.

[Prospective cohort study of pregnancy-induced hypertension and risk of preterm delivery and low birth weight].

OBJECTIVE: To determine the association between pregnancy-induced hypertension(PIH) and risk of preterm delivery (PD) and low birth weight (LBW). METHODS: A prospective cohort was established based on 131 867 women who delivered a singleton baby in seven cities or counties in Zhejiang province, China, during the period of 1995 - 2000. The exposure group included 14 278 women who were diagnosed as PIH, and the non-exposure group included 117 589 women. The exposure group was divided into mild, moderate, and severe subgroups based on the severity of PIH, and further divided into early, medium and late onset subgroups based on the time of onset of PIH (occurred in second trimester, third trimester, or during delivery). The primary outcome measures were the incidence of PD and LBW. Multiple logistic regression was used to estimate relative risk and 95% confidence intervals after adjustment by maternal age, occupation, education, parity, number of prenatal visits, gestational disease, caesarean delivery, pregnant body mass index, fetal sex, and gestational age (only for LBW). RESULTS: The incidence rates of PD and LBW in exposure group were 4.9% (701/14 278) and 3.6% (507/14 278), and both rates were higher than those of the non-exposure group (3.4% (4031/117 589), 1.8% (2110/117 589)) (chi(2) values were 80.8 and 202.0, P < 0.001). The incidence rates of PD in mild, moderate, and severe subgroups were 3.9% (404/10 358), 5.8% (181/3099), and 14.1% (116/821), and corresponding incidence rates of LBW were 2.5% (258/10 358), 4.9% (151/3099), and 11.9% (98/821). Both rates were increased with the severity of PIH (chi(2) values were 196.4 and 426.1, P-value for trend < 0.001). The incidence rates of PD in early, medium, and late onset subgroup were 8.4% (50/598), 5.7% (278/4867), and 4.2% (373/8813), and corresponding incidence rates of LBW were 5.7% (34/598), 4.2% (206/4867), and 3.0% (267/8813). Both rates were decreased by the time of PIH onset (chi(2) values were 115.4 and 239.8, P-value for trend < 0.001). CONCLUSION: PIH could increase the incidence of PD and LBW.

[Introduction to an individual-based standardization method -- propensity score weighting].

In this article, we presented the rationale and calculation procedures of a propensity score weighting method, with its application in epidemiological studies. The rationale for propensity score weighting method is similar to those for traditional standardization methods. Propensity score is used to estimate the weight for each individual. As the propensity score serves the function of observed covariates, the propensity score weighting can balance the distribution of the observed covariates between the comparison groups. There are two weighting methods according to the target standard populations: the Inverse probability of treatment weighting (IPTW) and the Standardized mortality ratio weighting (SMRW). Results of the example show that the distribution of the covariates tended to be consistent after weighting, and the IPTW and SMRW methods showed similar effect estimates. Propensity score weighting method can effectively balance the distribution of the confounding factors between the compared groups in non-randomized controlled trials.

[Influence of hemoglobin level during early gestation on the development of cognition of pre-school children].

OBJECTIVE: The purpose of this study was to evaluate the effect of hemoglobin (Hb) level during early gestation on the cognitive development of children at 4 - 6 years of age. METHODS: A total number of 3609 children were randomly selected from all the live birth infants whose mothers participated in a community intervention trial during 1993 - 1996 in 13 counties or cities in Jiangsu and Zhejiang provinces. Hb concentration during early gestation was measured at first prenatal examination and intelligence quotients (IQ), including full-scale, verbal and performance were assessed using Chinese-Wechsler Intelligence Scale for Children in 2000 - 2001 when these children had a mean age of 68 months. RESULTS: Compared with children whose mothers were non-anemic during early gestation, children whose mothers were anemic had a 0.6 point higher mean verbal scale IQ, a 0.9 point higher mean performance IQ and a 0.8 point higher mean full-scale IQ. These differences were not statistically significant when children's gender, age at intelligence test, region, parity and mother's IQ, education level and occupation were adjusted for. When mother-child pairs were divided into 5 sub-groups of every 20 percentiles according to Hb concentration during early gestation, verbal IQ scores of the lowest (Hb < 103 g/L), the moderate (110 g/L ≤ Hb < 116 g/L) and the highest Hb concentration group (Hb ≥ 124 g/L) were 91.6 ± 18.9, 92.8 ± 18.2 and 90.3 ± 18.6, respectively. The performance IQ scores were 104.7 ± 15.2, 104.5 ± 14.3 and 103.5 ± 15.1, and full-scale IQ scores were 97.8 ± 17.3, 98.4 ± 16.3 and 96.4 ± 17.4, respectively. After controlling for confounding factors, children whose mothers had highest Hb concentration were 54% (OR = 1.54, 95%CI: 1.13 - 2.11) more likely to have poor verbal scores and 53% (OR = 1.53, 95%CI: 1.10 - 2.12) more likely to have poor full-scale scores than children whose mothers had moderate Hb concentration. No statistical associations were noticed between high Hb concentration and performance scores, or between low Hb concentration during early gestation and verbal, performance as well as full-scale score of pre-school children. CONCLUSION: High maternal Hb concentration during early gestation might adversely affect children's cognitive development.

[Post-term pregnancy and associated social factors among pregnant women in Jiaxing city, China, 1993 to 2000].

OBJECTIVE: To understand the status of post-term pregnancy and associated social factors among pregnant women in Jiaxing city, from 1993 to 2000. METHODS: The study population consisted of 16 033 women who had delivered singleton live births in Jiaxing city,Zhejiang province, from 1993 to 2000. Chi-square test was employed to test the difference of proportions between respective groups. Multivariate logistic regression was conducted to examine the factors associated with post-term pregnancy. RESULTS: The incidence rates of post-term pregnancy were 8.7%, 10.6%, 9.4%, 7.4%, 4.3%, 2.6%, 3.3% and 4.0% from 1993 to 2000, respectively. Women who received premarital health care services had lower (5.6%) post-term incidence than those who did not (7.8%). Women who received county or above level health care services had lower (4.3%) post-term incidence than women who receive township level service (8.5%). Women who had primary school education had higher (11.5%) post-term incidence than women who received junior higher school education (6.8%), senior high school education (3.8%), or college education (2.9%), (P<0.001). Farmers had higher (9.5%) post-term incidence than workers in the rural areas (8.9%), in urban areas (4.3%) or women with other professions (4.2%). Women whose husbands were rural workers had higher (9.8%) post-term incidence than farmers (9.4%), urban workers (5.0%) or with other professions (3.6%, P<0.001). Data from multivariate logistic regression showed that the risk of post-term pregnancy was associated with the length and the level of using health care services together with schooling and occupation. CONCLUSION: The incidence of post-term pregnancy was decreasing in Jiaxing city during the period from 1993 to 2000 and the risk was associated with the length and level of health care service as well as the level of education and occupation of those women.

[Application of propensity score matching in the design of an epidemiological study].

INTRODUCTION: In this article, we presented the rationale and calculation procedures of the propensity score matching (PSM), and its application in the designing stage of an epidemiological study. Based on existing observational data, PSM can be used to select one or more comparable controls for each subject in 'treatment' group according to the propensity scores estimated by 'treatment' variable and main covariates. The results of an example analysis showed that the bias for main confounders between the treated and control samples declined more than 55% after PMS. CONCLUSION: PSM can reduce most of the confounding bias of the observational study, and can obtain approximate study effect to the randomized controlled trials when used in the designing of the epidemiological study.