Education,infant mortality,and low birth weight in Sweden 1973—1990: Emergence of the low birth weight paradox

Abstract

Aims: Educational differences in infant mortality, birth weight, and birth weight-specific infant mortality in Sweden were analysed. The ``low birth weight paradox'', where low birth weight infants have a lower mortality risk if born to women of lower rather than higher social strata, was addressed. Methods: The study includes about a million single births 1973—90 to women born 1946—60. There were 6,544 infant deaths and 35,334 low birth weight infants. Analysis conducted on six-year time periods was restricted to 652,859 births to women aged 25—32 at the time of delivery. Odds ratios and 95% CI were estimated by logistic regression. Birth weight-specific infant mortality rates were calculated by education. Results: Infants of women with low/low intermediate education had significantly higher odds ratios than those of highly educated women of being of low birth weight or of dying. If one compares only the infants of women with low and high education, these differences were accentuated over time. The low birth weight paradox appears over time. Conclusion: The widening differences in infant mortality and low birth weight over time may be caused by the decrease in women with low education, signifying increased selection and growing social disadvantage in this group. The emergence of the low birth weight paradox suggests that the distribution of causes of low birth weight differs between educational groups, and further that these causes are differently related to infant mortality. To disentangle these two groups of causes and their effects on infant mortality seems highly relevant.

Keywords

inequalities education infant mortality low birth weight low birth weight paradox

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References

Leon DA , Vågerö D. , Olausson PO Social class differences in infant mortality in Sweden: comparison with England and Wales. Br Med J 1992;305:687—91.

Haglund B. , Cnattingius S. , Nordström ML Social differences in late fetal death and infant mortality in Sweden 1985—86. Paediatr Perinat Epidemiol 1993;7:33—44.

Koupilova I. , Vågerö D. , Leon DA , Pikhart H. , Prikazsky V. , Holcik J. , et al. Social variation in size at birth and preterm delivery in the Czech Republic and Sweden, 1989—91. Paediatr Perinat Epidemiol 1998;12:7—24.

Vågerö D. , Koupilova I. , Leon DA , Lithell UB Social determinants of birthweight, ponderal index and gestational age in Sweden in the 1920s and the 1980s. Acta Paediatr 1999;88:445—53.

Helweg-Larsen K. , Olsen O. , Madsen M. Fødsler og sociale forhold. Copenhagen: National Institute of Public Health (DK), 1999 .

Arntzen A. , Magnus P. , Bakketeig LS Different effects of maternal and paternal education on early mortality in Norway. Paediatr Perinat Epidemiol 1993 ;7:376—86.

Arnzen A. , Samuelsen SO , Magnus P. , Bakketeig LS Birth weight related to social indicators in Norway. Eur J Public Health 1994;4:92—7.

Hemminki E. , Merilainen J. , Malin M. , Rahkonen O. , Teperi J. Mother's education and perinatal problems in Finland. Int J Epidemiol 1992;21:720—4.

North AF Jr , MacDonald HM Why are neonatal mortality rates lower in small black infants than in white infants in similar birth weight? J Pediatr 1977;90:809—10.

10.

Wilcox A. , Russell I. Why small black infants have a lower mortality rate than small white infants: the case for population-specific standards for birth weight. J Pediatr 1990 ;116:7—10.

11.

Shoham-Yakubovich I. , Barell V. Maternal education as a modifier of the association between low birthweight and infant mortality. Int J Epidemiol 1988;17:370—7.

12.

Carlson E. , Hoem JM Low-weight neonatal survival paradox in the Czech Republic. Am J Epidemiol 1999;149:447—53.

13.

Wilcox AJ Birth weight and perinatal mortality: the effect of maternal smoking. Am J Epidemiol 1993;137:1098—1104.

14.

Ericsson A. , Eriksson M. , Westerholm P. , Zetterström R. Pregnancy outcome and social indicators in Sweden. Acta Pediatrica Scand 1984;18:143—8.

15.

Cnattingius S. , Ericson A. , Gunnarskog J. , Källen B. A quality study of a medical birth registry . Scand J Soc Med 1990;18:143—8.

16.

StataCorp Stata User's Guide: Release 8: Stata Press, 2003.

17.

Arntzen A. , Moum T. , Magnus P. , Bakketeig LS The association between maternal education and postneonatal mortality. Trends in Norway, 1968—1991. Int J Epidemiol 1996;25:578—84.

18.

Jonsson JO , Mills C. The Swedish Level-of-Living Surveys: a general overview and description of the event history data. In: Jonsson JO , Mills C , editors. Cradle to Grave. Life-course change in modern Sweden. Durham: Sociologypress, 2001:228—42.

19.

Joseph KS , Kramer MS Recent trends in Canadian infant mortality rates: effect of changes in registration of live newborns weighing less than 500 g. CMAJ 1996;155: 1047—52.

20.

Nolte E. , Koupilova I. , McKee M. The increase in very-low-birthweight infants in Germany: artefact or reality ? Paediatr Perinat Epidemiol 2002 ;16:131—40.

21.

National Board of Health and Welfare (Sweden). Fakta om mammor, förlossningar och nyfödda barn, Medicinska födelseregistret 1973 till 2000 [Deliveries, mothers and newborn infants in Sweden, 1973—2000]; 2002. Report No. 2002-125-12.

22.

Skjaerven R. , Wilcox AJ , Oyen N. , Magnus P. Mothers' birth weight and survival of their offspring: population based study. Br Med J 1997;314:1376—80.

23.

Wen SW , Goldenberg RL , Cutter GR , Hoffman HJ , Cliver SP , Davis RO , et al. Smoking, maternal age, fetal growth, and gestational age at delivery. Am J Obstet Gynecol 1990;162:53—8.

24.

Kleinman JC , Pierre MB Jr , Madans JH , Land GH , Schramm WF The effects of maternal smoking on fetal and infant mortality. Am J Epidemiol 1988;127:274—82.

25.

Ericson A. , Gunnarskog J. , Kallen B. , Otterblad-Olausson P. Surveillance of smoking during pregnancy in Sweden, 1983— 1987. Acta Obstet Gynecol Scand 1991;70:111—7.

26.

Wilcox AJ On the importance — and the unimportance — of birthweight. Int J Epidemiol 2001;30:1233—41.

27.

Alberman E. Are our babies becoming bigger? J R Soc Med 1991;84:257—60.

28.

Bobak M. , Pikhart H. , Koupilova I. Neonatal mortality of low birthweight babies is increased in mothers with higher education. Br Med J 1997;315:886.

29.

Spencer NJ , Logan S. The treatment of parental height as a biological factor in studies of birth weight and childhood growth. Arch Dis Child 2002;87:184—7.