The Incidence Rate And Risk Factors Of Low Birth Weight In Some Areas Of China

Objective: 1. To know the incidence rate of low birth weight (LBW) in parts of China. 2. To know the the incidence rate of low birth weight during different areas, different times and different peoples;to explore whether have a peak of disease.3. To investigate the risk factors and clustering of these factors to low birth weight.4. To study whether low birth weight was associated with increased risk of infant morbidity and mortality.Subjects and methods:1. Subjects: We use a multi-stage, stratified, random cluster sampling method. At the first phase five provinces were randomly selected from North China, East China, Northwest China, Southwest China, and Northeast China; At the second phase five cities were randomly selected from five provinces above, the cities were Tongliao city, Changzhou city, Harbin city, Beijing area and Linxia city; The third stage a district ( county-level city ) and a county were selected by using Stratified random sampling during the selected cities above; The fourth stage in the selected districts and counties?were randomly selected a street, a town and a township which including number of the total population of 10 million or more respectively; the fifth stage were using census during the selected streets or towns. To ensure that the sample size for each point were selected more than 3, 300, A total of 16,954 infants who were born from Jan 1, 2006 to Dec 31, 2008 and their parents were enrolled in our survey.2. Methods: Cross-sectional study and multi-stage sampling method were used in this study. Trained investigators visited the subjects face to face. The content of questionnaire included (1) Infants demographic characteristics which included name, age, gender, nation, parity, feeding patterns, birth weight; (2) Infants'parents characteristics which included name, age, family income, concept which prefer boy, occuputation, education level; (3) mothers'health care situation which include numbers of checking during pregnancy, gestational age, diseases of mothers during pregnancy like pregnancy hypertension,anemia during pregnancy, diabetes, nephropathy, liver disease, etc; (4) the health conditions of infants which include the prevalence of disease, deformity and death; (5) the conditions and reasons of abortion and induction of labor. Statistical analysisEpidata3.1 software was used to establish a database, and all questionnaires were input after checking by two individuals. All p-values were based on a 2-sided test and a significance level of 0.05, and statistical analysis was conducted using SAS 9.2 statistical software.Results A total of 16954 participants including 9232 males and 7722 females were included in the analysis; the mean birth weight was 3.344±0.458 Kg.1. In the study, there were 487 infants with low birth weight, the incidence rate of low birth weight was 4.87%; there were 331 preterm infants, accounted for 68% during all the LBW infants; there were 156 small for gestational age infants, accounted for 32% during all the LBW infants; there were 11 infants of very low birthweight (VLBW) , accounted for 2.26% during all the LBW infants.2. The incidence of low birth weight due to the time, area and population varies.The incidence rate of LBW in rural was higher than urban ( 3.35%VS 2.47% ) ; With the increased parity, the incidence rate of LBW increased, like the low birth rate of 1 child was 2.14%, the low birth rate of 2 children was 5.24%, while the low birth rate of 3 children was 7.46%; Mothers'age <25 years old ( 3.24% ) and≥35 years old ( 4.43% ) had higher low birth weight rate than other age groups; Dongxiang ( 12.34% ) had a higher low birth weight rate while Mongolia ( 1.15% ) had a lower low birth weight rate; in 2007 ( 3.32% ) the incidence rate of low birth weight was higher than 2008 ( 2.46% ) .3. Circular distribution results show that in 2006 the incidence of low birth weight had a peak disease, the peak day was April 6, 2006, the interval were in the February 10, 2006 to May 31, 2006, there have no peak disease in 2007 and 2008; After three years of data combined, the incidence of low birth weight had a peak disease, the peak day was February 17.4. The mean birth weight during low birth weight infants was 2.165±0.249kg, while The mean birth weight during normal birth weight infants was 3.278±0.335kg. The proportion of urban infants ( 38.89% ), the proportion of males ( 46.71% ), the proportion of Han population ( 72.22% ), the proportion of mothers with high education level ( 17.01% ), parity is 1 ( 59.05% ) in the low birth weight group were lower than normal birth weight group; but the the ratio of pregnancy hypertension (8.85%), anemia during pregnancy ( 4.94% ), preterm delivery ( 30.66% ), maternal age <25 years ( 22.43% ) and≥35 years ( 11.73% ) were higher than normal birth weight infants.5. Univariate logistic regression analysis showed that Pregnancy hypertension, anemia, premature birth, baby girl, coming from rural areas, Dongxiang, parity, maternal age≥35 years were all risk factors for low birth weight, while mother s'high education level ( > grade 9 ) and Mongolian were protective factors for low birth weight ( all P <0.05 ).Multiple logistic regression analysis showed that Premature birth, pregnancy hypertension, girls, from rural areas, Dongxiang, parity 2 and parity3 were risk factors of low birth weight, and the odd ratios ( ORs ) and 95% confidence intervals ( 95% CIs ) were as follows: 17.65 ( 13.92～22.39 ) ,4.12 ( 2.78～6.11 ) ,1.45 ( 1.19～1.77 ) , 1.68 ( 1.32～2.13 ), 2.74 ( 1.98～3.79 ), 2.50 ( 1.94～3.23 ), 4.39 ( 3.06～6.29 ); With the increased parity, the occurrence of the risk of low birth weight increased either. Maternal age 29-34 years ( compared with <25 years ), mothers'education level> 12 ( compared with <9 grade ), Mongolia ( compared with Han ) were protective factors for low birth weight, and the odd ratios( ORs ) and 95% confidence intervals( 95% CIs ) were as follows: 0.66 ( 0.46～0.90 ), 0.41 ( 0.25～0.68 ).6. Multiple linear regression model showed that pregnancy hypertension can reduce the birth weight of 137g; preterm birth can reduce the birth weight of 516g; with increasing a level of parity, the birth weight can reduce 56g; baby coming from rural can reduce the birth weight of 80g; with increasing a level of maternal education, the birth weight can increase 33.96g; Dongxiang can reduce the birth weight of 213g; Mongolia can increase the birth weight of 95g.7. Infants of low birth weight had high clustering proportion ( 31.39% ) of 2 risk factors, including pregnancy hypertension, parity 2, anemia and preterm birth, than that in normal birth weight babies. After adjusting for Region, nation and other factors,the odds ratios ( 95%CI ) of low birth weight associated with the clustering of premature, parity,maternal hypertension, anemia were 6.31 ( 95%CI 5.02～7.93 ), 27.5 ( 95%CI 19.8～38.2 ), 35.0 ( 95%CI 15.7～78.4 ), respectively, compared with non—existence of the risk factor. Odds ratios of the clustering of two risk factors or more were all more than that of one risk factor. There is a clear dose-response relationship ( Trend test resultχ2 = 550.3, P <0.001 ).8. Infants morbidity ( 63.86% ) and mortality ( 1.85% ) during low birth weight group were higher than infants morbidity ( 58.90% ) and mortality ( 0.11% ) of normal birth weight. After adjusting for region, nation, gender and other factors, compared with normal birth weight, the disease OR ( 95% CI ) was 1.231 ( 1.020~1.486 ), the attributable risk percentage ( AR% ) was 7.77%; the OR ( 95% CI ) of infants mortality was 19.60 ( 8.490～45.27 ), the attributable risk percentage ( AR% ) was 94.05%.Conclusion:1. The incidence of low birth weight is different in different times, different regions and different people.2. Premature birth, pregnancy hypertension, girls, from rural areas, Dongxiang, parity 2 and parity 3 can increase the risk of low birth weight; Mongolia, high maternal education can reduce the risk of low birth weight.3. The risk factors to low birth weight exist clusting, the risk of low birth weight was increased with the number of clustering of risk factors in China.4. Low birth weight can increase the risk of Infants morbidity and mortality.