Skip Navigation


American Journal of Epidemiology Advance Access originally published online on February 19, 2007
American Journal of Epidemiology 2007 165(7):742-752; doi:10.1093/aje/kwk108
This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
165/7/742    most recent
kwk108v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Related articles in Am. J. Epidemiol.
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Search for citing articles in:
ISI Web of Science (1)
Right arrowRequest Permissions
Right arrow Disclaimer
Google Scholar
Right arrow Articles by Mumtaz, G.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Mumtaz, G.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

American Journal of Epidemiology Copyright © 2007 by the Johns Hopkins Bloomberg School of Public Health All rights reserved; printed in U.S.A.

ORIGINAL CONTRIBUTIONS

Effect of Consanguinity on Birth Weight for Gestational Age in a Developing Country

Ghina Mumtaz1, Hala Tamim2, Mona Kanaan3, Marwan Khawaja3, Mustafa Khogali4, Gerard Wakim5, Khalid A. Yunis1 for the National Collaborative Perinatal Neonatal Network

1 Department of Pediatrics, American University of Beirut Medical Center, Beirut, Lebanon
2 School of Kinesiology and Health Science, York University, Toronto, Ontario, Canada
3 Department of Epidemiology and Population Health, Faculty of Health Sciences, American University of Beirut, Beirut, Lebanon
4 Department of Family Medicine, American University of Beirut Medical Center, Beirut, Lebanon
5 Department of Pediatrics, Rizk Hospital, Beirut, Lebanon

Correspondence to Dr. Khalid Yunis, Pediatrics Department, Faculty of Medicine, American University of Beirut, P.O. Box 11-0236, Riad El-Solh, Beirut 1107 2020, Lebanon (e-mail: kayunis{at}aub.edu.lb).

Received for publication December 29, 2005. Accepted for publication March 24, 2006.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Consanguinity, the marriage between relatives, has been associated with adverse child health outcomes because it increases homozygosity of recessive alleles. The objective of this study was to assess the effect of consanguinity on the birth weight of newborns in Greater Beirut, Lebanon. Cross-sectional data were collected on 10,289 consecutive liveborn singleton newborns admitted to eight hospitals belonging to the National Collaborative Perinatal Neonatal Network during the years 2000 and 2001. Birth weight was modeled by use of the fetal growth ratio, defined as the ratio of the observed birth weight to the median birth weight for gestational age. A mixed-effect multiple linear regression model was used to predict the net effect of first- and second-cousin marriage on the birth weight for gestational age, accounting for within-hospital clustering of data. After controlling for medical and sociodemographic covariates, the authors found a statistically significant negative association between consanguinity and birth weight at each gestational age. No significant difference was observed in the decrease in birth weight between the first- and second-cousin marriages. Overall, consanguinity was associated with a decrease in birth weight for gestational age by 1.8% (ß = –0.018, 95% confidence interval: –0.027, –0.008). The largest effects on fetal growth were seen with lower parity and smoking during pregnancy.

birth weight; consanguinity; developing countries; gestational age; Lebanon

Abbreviations: NCPNN, National Collaborative Perinatal Neonatal Network


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 
Consanguinity, the marriage between relatives, has received a great deal of attention as a potential risk factor for many adverse health outcomes, because it favors the reemergence of recessive deleterious alleles that run in families. Stillbirths and spontaneous abortions, as well as infant death, have been shown to be positively correlated with consanguinity (1, 2). Consanguinity was also identified as a risk factor for several morbid conditions including congenital abnormalities and other birth defects (3, 4), mental retardation (5), deafness (6), ß-thalassemia (7), chronic renal failure (8), and neonatal diabetes mellitus (9). Consanguineous marriage has declined remarkably in many parts of the Western world, but it is still very common in the Middle East, especially among Arab communities (1, 10–13) where it is believed to preserve family ties (14).

Birth weight fits in a complex multifactorial framework of causality involving both genetic and nongenetic factors related to socioeconomic status and mothers' health (15–17). Many attempts have been made to investigate the presence of an association between consanguinity and birth weight reduction, but previous studies of the independent effect of consanguinity on birth weight are not in agreement. Although some researchers were unable to detect any relation (11, 18–23), a significant reduction in birth weight was identified by others (24–27). This can partially be explained by the difference in the genetic pools of the study populations (19, 22). Yet, the inconsistency in the results may be attributed to methodological flaws, namely, small sample size (20, 21, 23) and poor allowance for potential confounders (11, 18, 26). The association between consanguinity and birth weight remains inconclusive.

The objective of this study was to assess the effect of consanguinity on the birth weight of newborns in Greater Beirut, Lebanon, where consanguinity is relatively high. The presence of a large maternal neonatal database offering a large sample size and information on a considerable number of confounders makes the present study attractive.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 References
 
Study design
Cross-sectional data on consecutive liveborn singleton newborns admitted to eight hospitals in Greater Beirut, Lebanon, during the period from January 1, 2000, to December 31, 2001, were collected through the National Collaborative Perinatal Neonatal Network (NCPNN). Since its establishment in 1997, the NCPNN has maintained an integrated perinatal neonatal database where data are collected daily at participating hospitals by trained midwives, nurses, and research assistants using a standardized instrument. The data collected cover sociodemographic and medical information. Data sources included direct interviews with admitted mothers and also review of obstetric and nursery charts.

Study variables
Information on consanguinity was collected through direct interviews with admitted mothers. Parental consanguinity was classified into three categories: first-cousin marriages (the baby's parents are cousins), second-cousin marriages (the baby's grandparents are cousins), and not related. To account for differences in gestational age, birth weight was modeled by use of the fetal growth ratio, defined as the ratio of the observed birth weight to the median birth weight for gestational age, as obtained from recently developed sex-specific fetal growth charts for the NCPNN newborn population at 28–42 weeks' gestation (28). Fetal growth ratio was the preferred measure of fetal growth in several published papers, because it conveys information about the relative degree of under- or overweight compared with the median at each gestational age, and because it is used as a continuous variable in statistical analysis (29, 30). Birth weight was measured, in grams, upon admission to the nursery and immediately reported on the baby's medical chart. Gestational age was calculated in completed weeks by use of ultrasonic examinations of the fetus, 96.5 percent of which were performed during the first or early second trimesters. In 285 cases (2.8 percent) where ultrasonic examination was not available, gestational age was calculated by use of the last menstrual period.

The other variables considered in the study as potential confounding variables relate to characteristics of the newborn and his/her parents. The newborn's characteristics were sex and the presence at birth of congenital malformation. Congenital malformations were diagnosed by attending physicians by physical examination of the newborn and using, when needed, specific tests such as an echocardiogram, karyotyping, and others. Sociodemographic characteristics included information on the father's religion, maternal age at delivery, maternal and paternal education and occupation, and household crowding. The maternal characteristics considered included obstetric history (parity, previous abortion, birth spacing, and prenatal care); anthropometric measurements (height and prepregnancy weight); pregnancy complications (hypertension, preeclampsia, bleeding, and gestational diabetes); and nutrition and behavior during pregnancy (pregnancy weight gain and cigarette and/or arguileh smoking). A common tradition in the Arab world, arguileh smoking (also known as water-pipe smoking) is done through a special device, whereby humidified tobacco is burned with a charcoal ember and the smoke formed passes through the device into water before being inhaled through a long, flexible pipe.

Study population
During the period from January 1, 2000, to December 31, 2001, a total of 13,564 singleton newborns were admitted at the eight participating hospitals. Newborns were excluded from the study if they had data missing on consanguinity (n = 2,995), birth weight (n = 72), or gestational age (n = 262). Newborns with gestational age greater than 42 weeks or less than 28 weeks were excluded from the study population (n = 34). A total of 93 cases with missing newborn sex were also deleted because sex-specific growth charts were used for the definition of fetal growth ratio. As such, the study population consisted of a total of 10,289 newborns that were considered in the analysis.

Analysis
Analysis was done with STATA, version 7.0 (StataCorp LP, College Station, Texas), statistical software and R-language, version 1.8.1. Bivariate analysis of consanguinity with the different sociodemographic and other medical covariates was performed by use of the chi-squared test, in order to define the characteristics of the population under study. The difference in the mean fetal growth ratio across the different categories of consanguinity and the other covariates was tested by analysis of variance or the Student t test. Two-tailed p values were calculated, and significance was set at 5 percent. Unadjusted fetal growth ratio differences are presented.

Multiple mixed-effects linear regression was used to predict the net effect of consanguinity on the fetal growth ratio, with adjustment for the confounding effect of the other covariates that proved to be significantly associated with fetal growth ratio at the bivariate level (p < 0.2). Linearity between fetal growth ratio and the continuous covariates was verified in the regression model by performing residuals analysis. Because data were collected from eight hospitals in Beirut, a mixed-effects linear model was used to account for the within-hospital clustering of the data (31, 32). There was a concern that congenital malformations, pregnancy complications, and history of previous abortions might be intermediate outcomes of pregnancy and that their inclusion in the model would result in an underestimate of the effect of consanguinity and other potential factors. Therefore, these covariates were not included in the final regression model. However, for further reassurance, an additional regression model including the above-mentioned potential mediators was carried out, and there was no noticeable change in the regression coefficients. The reported results reflect the former model.

Prior to the regression, the data set was multiply imputed for missing data. This method replaces each missing value with a set of plausible values that represent the uncertainty about the right value to impute. The different imputed data sets obtained are then analyzed by standard procedures, and results are finally pooled for the inference (33). Multiple imputation was done using switching regression (34). Ten sets of imputations with 20 cycles each were performed, and all the covariates that were entered in the final regression model were imputed for their missing values. The highest rates of missing data were observed with prepregnancy weight (10.1 percent), maternal height (10.6 percent), and weight gain (21.7 percent). Estimates from the 10 imputations were pooled by use of Rubin's rules for multiple imputation inference for scalar estimates (35–37).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 References
 
Table 1 describes the characteristics of the study population by degree of consanguinity. Consanguineous couples were mainly Muslims of lower socioeconomic status, as shown with the significant negative association between consanguinity and parental education, occupation, and household crowding index. First- and second-cousin marriages were also significantly associated with lower maternal age, higher parity, and less adequate prenatal care. On average, mothers in a consanguineous union had higher prepregnancy weight and lower weight gain, and they also smoked cigarettes and/or arguileh more than did mothers from unrelated unions. The proportions of mothers having a previous abortion and of current babies having congenital malformations increased with increasing consanguinity levels. On the other hand, there was no significant association between consanguinity and newborn sex, as well as with any of the pregnancy complications (table 1).


View this table:
[in this window]
[in a new window]

  		TABLE 1. Characteristics of the study population by consanguinity level in Greater Beirut, Lebanon, National Collaborative Perinatal Neonatal Network, 2000–2001

 
At the bivariate level, there was a significant negative association between consanguinity and birth weight (p = 0.004), with second- and first-cousin marriages leading to a decrease of, respectively, 1.7 and 1.5 percent in birth weight for gestational age (table 2). The multiple linear regression model assessing the independent effect of consanguinity on the fetal growth ratio included variables that were significant determinants of the fetal growth ratio at the bivariate level. These were, as can be seen in table 2, maternal age, all measures of socioeconomic status, parity, prenatal care, maternal anthropometric measurements, pregnancy weight gain, smoking, history of previous abortion, maternal hypertensive disorders and diabetes, and congenital malformations among the newborn. As the different socioeconomic indicators, namely, maternal and paternal education and occupation, religion, and crowding index, were found to be collinear, only maternal education and paternal occupation were included in the model, as they were identified in the literature to be important predictors of birth weight (38, 39). The newborn's sex was not included in the regression, as it was adjusted for in the definition of fetal growth ratio when sex-specific growth charts were used.


View this table:
[in this window]
[in a new window]

  		TABLE 2. Bivariate associations between parental and fetal variables and fetal growth ratio among newborns in Greater Beirut, Lebanon, National Collaborative Perinatal Neonatal Network, 2000–2001

 
Table 3 summarizes the results of the multiple mixed-effects linear regression. After controlling for the other covariates and accounting for the within-hospital clustering of the data, we found that the negative association between consanguinity and birth weight remained statistically significant. On the average, babies born to second cousins and first cousins were, respectively, 1.9 percent and 1.6 percent lighter than those of unrelated parents. No statistically significant difference was observed in the decrease in fetal growth ratio between the first- and second-cousin marriages. It is worth mentioning that the intraclass correlation coefficient was equal to 0.6 percent. Moreover, the regression model was performed on the unimputed data file, and the observed associations were in the same directions with respect to all covariates in the model, including consanguinity.


View this table:
[in this window]
[in a new window]

  		TABLE 3. Multiple linear regression model for the net effect of consanguinity on the fetal growth ratio of newborns in Greater Beirut, Lebanon, National Collaborative Perinatal Neonatal Network, 2000–2001*

 
As a check on whether consanguinity was an important factor in explaining the variation in fetal growth ratio, the final regression model performed was compared with a similar model containing all the covariates without consanguinity. Based on the likelihood ratio test and the Akaike Information Criterion, the contribution of consanguinity in explaining the variation in fetal growth ratio was statistically significant.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
References
 
A major strength of the present study is that it benefited from the availability of information on a considerable number of factors that may confound the association between consanguinity and birth weight. With fetal growth having a multifactorial nature of causation, such a comprehensive adjustment of confounding enabled the assessment of the independent effect of consanguinity. Results of the present study indicated that, after controlling for confounders, overall consanguinity (first- and second-cousin marriage) was associated with a statistically significant decrease in birth weight for gestational age by 1.8 percent compared with that of newborns of unrelated parents (ß = –0.018, 95 percent confidence interval: –0.027, –0.008), with no significant difference in birth weight for gestational age reduction between the first- and second-cousin marriages.

In the literature, there is no agreement on the effect of consanguinity on birth weight (table 4) and especially that fetal growth is affected by both genetic and environmental factors. Our study results are in concordance with those of Jaber et al. (25), Kulkarni and Kurian (26), Sibert et al. (27), and Morton (24), who reported a significant decrease in the mean birth weight of newborns born to consanguineous parents. In all of the previous literature, the outcome under study was simple birth weight, with no adjustment for gestational age, as opposed to the present study where the observed birth weight was compared with the median birth weight at each gestational age through the fetal growth ratio. Usually, a difference of 5 percent in the fetal growth ratio represents, for a full-term infant, an average difference of 170 g (29). Our study results revealed a 1.8 percent decrease in birth weight for gestational age associated with consanguinity. The same pattern was observed in all similar studies in the literature, whereby the reduction in mean birth weight ranged from 20 to 211 g in one extreme case (25) (table 4). The explanatory factors that had the greatest impact on the fetal growth of newborns in Beirut included lower parity and smoking during pregnancy. This is in agreement with previous studies that have stressed the importance of such factors on birth weight (29, 40, 41).


View this table:
[in this window]
[in a new window]

  		TABLE 4. Summary of the literature on the effect of consanguinity on birth weight

 
One limitation of the present study is that a substantial proportion of cases had missing information on the main exposure, consanguinity, and were thus deleted from the original sample. However, there are no reasons to suspect that the missingness followed any particular pattern in relation to the exposure and/or outcome. The main reason behind the observed rate of missing consanguinity is that, depending on the workload and on the staff availability in the delivery room and the nursery, the nurses responsible for data collection might drop the whole interview with the mother, including information on consanguinity. This is exacerbated with early postpartum discharge of mothers from the hospital (less than 24 hours), a common observation in the network hospitals. Moreover, the question regarding consanguinity is not particularly sensitive in our community, as consanguinity has always been part of the social and cultural norms of the Lebanese populations. Consanguineous marriages (including distant relatives) are common and account for 21 percent of all marriages in Lebanon (42), with rates showing variations between regions and ranging from 15 percent in the capital Beirut up to 50 percent in certain rural areas (43). The idea that consanguinity might be associated with lower birth weight is also practically nonexistent. As such, there are no reasons why related parents of relatively smaller babies might want to hide their consanguinity levels, and any underreporting of consanguinity, if present, is expected to be equally distributed among infants of all birth weights.

On the other hand, imputation of the missing values for the covariates was performed by use of multiple imputation. This technique has become the most recommended approach for handling missing data, because it accounts for the between-imputation variability and has been shown to provide statistically valid inferences (44, 45). Imputation of the missing values allowed us to increase the power and efficiency of our sample and to minimize bias.

This was a multicenter study involving major hospitals in Beirut. With the study sample covering over 20 percent of the Greater Beirut births and with over 94 percent of deliveries occurring in hospitals (42, 46), the findings are thus representative of the city of Beirut and its suburbs. They indicate that consanguinity is associated with a reduction in the birth weight for gestational age among infants in Greater Beirut. Assessing the effect of consanguineous marriages on different neonatal health outcomes, such as prematurity, birth defects, and others, remains attractive in a relatively highly inbred population such as the Lebanese population.


   ACKNOWLEDGMENTS
 
This work was partially supported by funds from the World Health Organization; the Lebanese National Council for Scientific Research; and the Medical Practice Plan, the University Research Board, and the Pediatrics Chairman's fund at the American University of Beirut.

The authors would like to acknowledge the following National Collaborative Perinatal Neonatal Network investigators that were involved in data collection at the network institutions: Dr. Alia Aaraj (Rassoul Aazam Hospital), Dr. Mona Alameh (Sahel General Hospital), Dr. Philippe Chedid (Lebanese University), Dr. Imad Chokr (Middle East Hospital), Dr. Mohammad Itani (Najjar Hospital), Dr. Imad Melki (Hotel Dieu de France Hospital), Dr. Fadlallah Nassif (St. Charles Hospital), Dr. Yolla Nassif (St. Georges Hospital), Dr. Mariam Rajab (Makassed General Hospital), Dr. Gerard Wakim (Rizk Hospital), and Dr. Khalid Yunis (American University of Beirut Medical Center).

Conflict of interest: none declared.


   References
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 References
 

  1. Mokhtar MM and Abdel Fattah MM. (2001) Consanguinity and advanced maternal age as risk factors for reproductive losses in Alexandria, Egypt. Eur J Epidemiol 17:559–65.[CrossRef][Web of Science][Medline]
  2. Stoltenberg C, Magnus P, Lie RT, et al. (1998) Influence of consanguinity and maternal education on risk of stillbirth and infant death in Norway, 1967 –1993. Am J Epidemiol 148:452–9.[Abstract/Free Full Text]
  3. Rittler M, Liascovich R, Lopez-Caelo J, et al. (2001) Parental consanguinity in specific types of congenital anomalies. Am J Med Genet 22:36–43.
  4. Stoll C, Alembik Y, Dott B, et al. (1994) Parental consanguinity as a cause of increased incidence of birth defects in a study of 131,760 consecutive births. Am J Med Genet 49:114–17.[CrossRef][Web of Science][Medline]
  5. Durkin M, Khan N, Davidson L, et al. (2000) Parental and postnatal risk factors for mental retardation among children in Bangladesh. Am J Epidemiol 152:1024–33.[Abstract/Free Full Text]
  6. Zlotogora J. (1997) Genetic disorders among Palestinian Arabs: effects of consanguinity. Am J Med Genet 68:472–5.[CrossRef][Web of Science][Medline]
  7. Basson P. (1979) Genetic disease and culture patterns in Lebanon. J Biosoc Sci 11:201–7.[Web of Science][Medline]
  8. Hamed R. (2002) The spectrum of chronic renal failure among Jordanian children. J Nephrol 15:130–5.[Web of Science][Medline]
  9. Soliman A, Elzalabany M, Bappal B, et al. (1999) Permanent neonatal diabetes mellitus: epidemiology, mode of presentation, pathogenesis and growth. Indian J Pediatr 66:363–73.[Medline]
  10. Hijazi Z and Haidar MZ. (2001) Influence of consanguinity and IgE receptor genotypes on clinical manifestations of asthma in Kuwaiti children. J Trop Pediatr 47:13–16.[Medline]
  11. al-Abdulkareem AA and Ballal SG. (1998) Consanguineous marriages in an urban area of Saudi Arabia: rates and adverse health effects on the offspring. J Community Health 23:75–83.[CrossRef][Web of Science][Medline]
  12. Al Ghazali LI, Bener A, AbdulRazzak YM, et al. (1997) Consanguineous marriages in the United Arab Emirates. J Biosoc Sci 29:491–7.[CrossRef][Web of Science][Medline]
  13. Khouri SA and Massad D. (1992) Consanguineous marriage in Jordan. Am J Med Genet 43:769–75.[CrossRef][Web of Science][Medline]
  14. Khlat M and Khudr A. (1984) Cousin marriages in Beirut, Lebanon: is the pattern changing? J Biosoc Sci 16:369–73.[Web of Science][Medline]
  15. Spencer N and Logan S. (2002) Social influences on birth weight. J Epidemiol Community Health 56:326–7.[Free Full Text]
  16. Wilcox MA, Smith SJ, Johnson IR, et al. (1995) The effect of social deprivation on birthweight, excluding physiological and pathological effects. Br J Obstet Gynaecol 102:918–24.[Web of Science][Medline]
  17. Clausson B, Lichtenstein P, Cnattingius S. (2000) Genetic influence on birthweight and gestational length determined by studies in offspring of twins. BJOG 107:375–81.[Medline]
  18. Basaran N, Artan S, Yazicioglu S, et al. (1994) Effects of consanguinity on anthropometric measurements of newborn infants. Clin Genet 45:208–11.[Web of Science][Medline]
  19. Khlat M. (1989) Inbreeding effects on fetal growth in Beirut, Lebanon. Am J Phys Anthropol 80:481–4.[CrossRef][Web of Science][Medline]
  20. Honeyman MM, Bahl L, Marshall T. (1987) Consanguinity and fetal growth in Pakistani Moslems. Arch Dis Child 62:231–5.[Abstract/Free Full Text]
  21. Asha Bai PV and John TG. (1982) The effect of consanguinity on the gestation period and anthropometric traits of the newborn in southern India. Trop Geogr Med 34:225–9.[Web of Science][Medline]
  22. Rao PSS and Inbaraj SG. (1980) Inbreeding effects on fetal growth and development. J Med Genet 17:27–33.[Abstract/Free Full Text]
  23. Fried K and Davies M. (1974) Some effects on the offspring of uncle-niece marriage in the Moroccan Jewish community in Jerusalem. Am J Hum Genet 76:65–72.
  24. Morton NE. (1958) Empirical risks in consanguineous marriages: birth weight, gestation time, and measurements of infants. Am J Hum Genet 10:344–9.[Web of Science][Medline]
  25. Jaber L, Merlob P, Gabriel R, et al. (1997) Effect of consanguineous marriage on reproductive outcome in an Arab community in Israel. J Med Genet 34:1000–2.[Abstract/Free Full Text]
  26. Kulkarni ML and Kurian M. (1990) Consanguinity and its effect on fetal growth and development: a south Indian study. J Med Genet 27:348–52.[Abstract/Free Full Text]
  27. Sibert JR, Jadhav M, Inbaraj SG. (1979) Fetal growth and parental consanguinity. Arch Dis Child 54:317–19.[Abstract/Free Full Text]
  28. Yunis KA, Khawaja M, Beydoun H, et al. Intrauterine growth standards in a developing country: a study of single live births at 28 to 42 weeks' gestation. Paediatr Perinat Epidemiol (in press).
  29. Kramer MS, Olivier M, McLean FH. (1990) Determinants of fetal growth and body proportionality. Pediatrics 86:18–26.[Abstract/Free Full Text]
  30. Wen SW, Kramer MS, Usher RH. (1995) Comparison of birth weight distributions between Chinese and Caucasian infants. Am J Epidemiol 141:1177–87.[Abstract/Free Full Text]
  31. Pinheiro JC and Bates DM. (2000) Mixed effects models in S and S-PLUS 1st ed (Springer Verlag, New York, NY).
  32. Raundenbush SW and Bryke AS. (2002) Hierarchical linear models: applications and data analysis methods 2nd ed (Sage Publications, Thousand Oaks, CA).
  33. Yuan YC. (2000) Multiple imputation for missing data: concepts and new development. Proceedings of the Twenty-fifth Annual SAS Users Group International Conference, Indianapolis, Indiana, April 9–12, 2000. Paper 267(SAS Institute, Inc, Rockville, MD) (http://www.ats.ucla.edu/stat/sas/library/multipleimputation.pdf).
  34. Van Buuren S, Boshuizen HC, Knook DL. (1999) Multiple imputation of missing blood pressure covariates in survival analysis. Stat Med 18:681–94.[CrossRef][Web of Science][Medline]
  35. Rubin DB and Schenker N. (1991) Multiple imputation in health-care databases: an overview and some applications. Stat Med 10:585–98.[Web of Science][Medline]
  36. Schafer JL and Olsen MK. (1998) Multiple imputation of multivariate missing-data problems: a data analyst's perspective. Multivariate Behav Res 33:545–71.
  37. Schafer JL and Yucel RM. (2002) Computational strategies for multivariate linear mixed models with missing values. J Comput Graph Stat 11:421–42.
  38. Clausson B, Cnattingius S, Axelsson O. (1998) Preterm and term births of small for gestational age infants: a population-based study of risk factors among nulliparous women. Br J Obstet Gynaecol 105:1011–17.[Web of Science][Medline]
  39. Golding J and Shenton T. (1990) Low birth-weight and pre-term delivery in South-East Asia. The WHO international collaborative study of hypertensive disorders of pregnancy. Soc Sci Med 30:497–502.[CrossRef][Web of Science][Medline]
  40. Wen SW, Goldenberg RL, Cutter GR, et al. (1990) Intrauterine growth retardation and preterm delivery: prenatal risk factors in an indigent population. Am J Obstet Gynecol 162:213–18.[Web of Science][Medline]
  41. Mohsin M, Wong F, Bauman A, et al. (2003) Maternal and neonatal factors influencing premature birth and low birth weight in Australia. J Biosoc Sci 35:161–74.[CrossRef][Web of Science][Medline]
  42. Republic of Lebanon Ministry of Public Health. (1998) Lebanon maternal and child health survey: principal report(Republic of Lebanon and the Pan Arab Project for Child Development (PAPCHILD) of the League of Arab States, Beirut, Lebanon).
  43. United Nations Children's Fund. (2000) The state of children in Lebanon 2000(UNICEF, New York, NY).
  44. Arnold A and Kronmal RA. (2003) Multiple imputation of baseline data in the Cardiovascular Health Study. Am J Epidemiol 157:74–84.[Abstract/Free Full Text]
  45. Barzi F and Woodward M. (2004) Imputation of missing values in practice: results from imputations of serum cholesterol in 28 cohort studies. Am J Epidemiol 160:34–45.[Abstract/Free Full Text]
  46. Republic of Lebanon Ministry of Environment. Lebanon state of the environment report (2001) (Republic of Lebanon, Beirut, Lebanon) (http://www.studies.gov.lb/Cultures/en-US/tContent/Sectors/Local+Development+and+Environment/Environment/ENV-b/ENVI-b0-2001-002.htm).

Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us    What's this?

Related articles in Am. J. Epidemiol.:

Genetic and Environmental Influences on Birth Weight, Birth Length, Head Circumference, and Gestational Age by Use of Population-based Parent-Offspring Data
Astrid Lunde, Kari Klungsøyr Melve, Håkon K. Gjessing, Rolv Skjærven, and Lorentz M. Irgens
Am. J. Epidemiol. 2007 165: 734-741. [Abstract] [FREE Full Text]  



This article has been cited by other articles:


Home page
 NeoReviewsHome page
K. Yunis, R. E. Rafei, and G. Mumtaz
International Perspectives: Consanguinity: Perinatal Outcomes and Prevention - A View from the Middle East
NeoReviews, February 1, 2008; 9(2): e59 - e65.
[Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
165/7/742    most recent
kwk108v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Related articles in Am. J. Epidemiol.
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Search for citing articles in:
ISI Web of Science (1)
Right arrowRequest Permissions
Right arrow Disclaimer
Google Scholar
Right arrow Articles by Mumtaz, G.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Mumtaz, G.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?