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To examine the impact of pregnancy termination before 28 weeks of gestation on the overall prevalence of neural tube defects (NTDs).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.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 of28 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.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.

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.

To understand the distribution of birth weight among premature infants and the associated social factors.The study population consisted of 97 537 women who delivered singleton live birth of 20 to 41 gestational weeks in 4 counties/cities, Jiangsu and Zhejiang provinces, China from 1995 to 2000. Chi-square test was employed to test the difference of proportions between respective groups. One- way ANOVA was used to test the differences regarding the mean of gestational weeks at the first prenatal visit and the mean of prenatal visits between the two groups. Multivariate logistic regression was conducted to examine the factors associated with premature birth.Women aged 35 years had higher (8.8%) premature incidence than those aged less than 24 years (5.6%), 25 - 29 years (4.6%), or 30 - 34 years (4.5%, P0.001). Women with height less than 149 cm had higher (6.8%) premature incidence than those with height taller than 150 cm (5.0%). Women whose BMI were at least 28 and 24 - 28 had higher (5.5%, 5.5%) premature incidences than those whose BMI were 18.5 - 24.0 (5.0%),18.5 (4.6%, P0.001). The incidence of premature birth was 6.0% among women without previous pregnancy, higher than that among those women with 4 times of pregnancies (5.7%), 2 times of pregnancies (4.3%), and 3 times of pregnancies (4.0%). Parous women with at least two deliveries had higher (9.3%) premature incidence than the primiparous women (5.2%) and whose women with only one delivery (4.5%, P0.001). Women who received early prenatal care had lower 4.7% premature incidence than those who did not receive the service (6.1%). The mean times of prenatal visits among women with premature births was 8.53, less than that of those with full term delivery (10.97). Women with less than four times of prenatal visit had higher (18.9%) premature incidence than those with at least five prenatal visits (4.9%). Multivariate logistic regression showed that premature delivery risk was associated with age, height, BMI, gravidity, parity, early prenatal care, the mean of gestational weeks at first prenatal visit and the mean number of prenatal visits etc.Premature delivery risk was associated with factors as age, height, BMI, gravidity, parity, early prenatal care, the mean of gestational weeks at first prenatal visit, the mean number of prenatal visits etc.

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.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.

To explore the relationship between maternal passive smoking during early pregnancy and the risk of neural tube defects (NTDs).Data was derived from a population-based case-control study on birth defects in Shanxi province. The study subjects included 515 NTDs defects cases (236 cases of anencephaly, 237 spina bifida and 42 encephalocele) ascertained during January 2003 and June 2007 in the study areas and 682 normal controls randomly selected in the same residence during the same period as cases. RESULTS; The risk of NTDs in their offspring was 1.84 (95% CI: 1.39-2.44) for mothers with passive smoking history during peri-conceptional period. There was a marked dose-response relation between maternal passive smoking and the risk of NTDs in offspring. Compared to the women without passive smoking, the NTDs risk in offspring was 1.51 for women with occasional passive smoking and 2.44 for women with passive smoking for almost everyday during the peri-conceptional period.Maternal passive smoking during peri-conceptional period increased the risk of NTDs in offspring.

Dietary factors that could potentially be related to the risk of birth defects are still unknown in Shanxi province, a region with high prevalence of neural tube defects(NTDs) in China. The main aim of this study was to evaluate the association between NTDs and local dietary factors.A population-based case-control study was conducted during 2003-2005 in four selected counties of Shanxi province with 363 NTDs cases ascertained and 523 control babies without any external birth defects.By multivariate logistic regression analysis, we found the NTDs risk was significantly associated with low consumption of meat and legume, high consumption of pickled vegetables, noncentralized supply of drinking water and drinking tea after adjusting for maternal education level and birth defects history. A significant dose response trend was found between the NTDs risk and the lower frequencies of meat and legume consumption and higher frequency of pickled vegetable consumption, with population attributable risks (PAR) of 69.4%, 22.0% and 18.5%, respectively. Mothers who got their drinking water from river or pond during periconceptional period were more likely to have a NTD-affected pregnancy [OR = 3.42, 95% CI: 1.44-8.09, population attributable risk (PAR) = 4.7%] compared with those who utilized tap or well water. Those who drank tea everyday had an elevated risk of having a NTD-affected pregnancy compared with those who didn't (OR = 4.65, 95% CI: 1.41-15.36, PAR = 2.6%).Higher intake of meat and legume protects a woman from having a NTD-affected pregnancy, and consumption of pickled vegetables, drinking water from river or pond and drinking tea everyday increase the risk of having such a pregnancy in the study population.

To compare plasma and red blood cell folate levels among women in their first trimester of pregnancy from rural areas with high or low prevalence of neural tube defects.A cross-sectional study was performed, among women in their first trimester of pregnancy from rural areas with high or low prevalence of neural tube defects in 2003. Non-fasting blood sample were collected and analyzed for plasma and red blood cell folate concentrations for 688 women.The median plasma (10.53 nmol/L) and red blood cell folate (389.2 nmol/L) among women from the high prevalence rural area were lower than those of women from the low prevalence rural area (plasma folate: 30.39 nmol/L, red blood cell level folate: 926.0 nmol/L). Among women from the high prevalence area, about 50% and 43% were respectively, deficient for plasma and red blood cell folate, compared with 6% and 4% respectively, for women from the low prevalence area. The median plasma folate levels among women who took periconceptional folic acid supplements in both high and low prevalence areas were about twice higher than those who did not take the folic acid. The median red blood cell folate level of the folic acid users was 40% higher than those of the non-users. Among those who took folic acid, women in the low prevalence area had 70%-90% higher plasma folate concentration and twice higher red cell folate concentration than women in the high prevalence area.Women from the rural area with a high prevalence of neural tube defects had low plasma and red blood cell folate levels. Periconceptional supplementation with folic acid could substantially improve folate status of reproductive-aged women. However, supplementation with 0.4 mg of folic acid per day might be inadequate for women in the high prevalence rural area.

To evaluate the reliability of the birth defects surveillance system in four counties with high prevalence of birth defects (Pingding, Xiyang, Taigu and Zezhou counties) in Shanxi province, China.One township was selected from each county as study site. The health workers chosen from township or village level were trained to visit families on the outcomes of each pregnancy who gave birth during year 2003 in the study site. The number of births and cases collected in the study were compared with that from the surveillance system. The number of births reported by surveillance system in four counties was also compared with the data from the local government. The criteria of evaluation were: 1) number of the missing report of births shouldor = 5%, 2) the number of missing report on major external birth defects cases shouldor = 10%. Researchers from the Peking University were responsible for examining the quality of surveillance in some terminal units of surveillance system.The numbers of births reported in the study and from the surveillance system for four-township were 1043 and 997, respectively. 46 births were missing and the rate of misreporting for births was 4.4%. The numbers of birth defects cases reported in the study and from the surveillance system were 30 and 29, respectively. 1 case of birth defect as missed, and rate of misreporting for birth defects cases was 3.3%. The total number of births reported from surveillance was similar to that in the study in four counties, with a difference of 1.2%. Birth registry data was rather readable and special health workers responsible for surveillance work were present in all the terminal units of the surveillance system.The misreporting of births and cases existed in the birth defects surveillance system of the four counties in Shanxi province, but were lower than the allowable criteria. The surveillance units had better registration, reporting and administration of births and birth defect cases. Hence, the quality of the data from the surveillance system in these four counties was reliable.

To study the association between reduced folate carrier gene (RFC1 A80G) polymorphism and the risk for child with neural tube defects (NTDs), and to provide epidemiological evidence for the existence of NTDs genetic marker.RFC1 (A80G) genotypes were detected using RFLP-PCR for blood DNA of 104 families with NTDs-affected children and 100 control families with no history of child-affected birth defects. Case-control study and transmission/disequilibrium test(TDT) for the RFC1 genotype of NTDs pedigree were carried out.The G allele frequency of children with NTDs was higher than that of controls when compared to A allele( OR = 1. 64, 95% CI :1.08-2.49). The offspring of the GG genotype were associated with a 2.56-fold increased risk of NTDs when compared to the AA genotype (OR = 2.56, 95% CI: 1.04-6.36) in our study population. There was evidence of association between G allele and the risk of parent having a child with NTDs (OR = 1.56, 95% CI: 1.07-2.28) in the TDT analysis.Our findings indicated that there was potential association between offspring RFC1 GG genotype and the risk of NTDs, and the G allele was a possible susceptible gene marker for an increased NTDs risk in the Chinese population.

To study the prevalence rates of birth defects in high and low risk areas in China.A population-based surveillance system on birth defects was used to obtain the prevalence rates of 24 kinds of major external birth defects fromor = 20 weeks of gestation to 7 days of life in selected areas in Shanxi and Jiangsu provinces.The birth prevalence of birth defects (232.4 per 10,000 births) and neural tube defects (NTDs) (138.7 per 10,000 births) in four counties of Shanxi province were significantly higher than that in Taiyuan city (75.3 and 28.2 per 10,000 births, respectively). There was no significant difference for all selected birth defects between Wuxi city and Xishan counties in low risk areas. There was a 6.1-fold of higher prevalence for NTDs in Taiyuan city compared with that in Wuxi areas (4.6 per 10,000 births). In four counties of Shanxi province, the prevalence rates of anencephaly, spina bifida, hydrocephaly, cleft palate alone and polydactyly were significantly higher than in Wuxi areas. The NTDs prevalence rate in four counties of Shanxi was 30.2 times higher than in Wuxi areas. When compared with previous surveillance data, the NTDs prevalence rate did not present obvious declining trend in high risk areas. The birth prevalence rate had a 31.8% decrease when births were calculated after 28 gestational weeks and compared with those from 20 gestational weeks.NTDs remained to be the most common birth defect seen in Shanxi province. The birth prevalence rate of NTDs in some areas of Shanxi province was among the highest that ever reported in the world in comparison with data from other countries and regions. The current prevalence rate in high risk areas in Shanxi province did not clearly show a declining trend. Programs on surveillance and prenatal diagnosis were proved to have made big impact on the rates of major external birth defects.