Can children's health be predicted by perinatal health?

David A Sauitz

The University of North Carolina at Chapel Hill, Campus Box 7400, McGavran-Greenberg Hall, Chapel Hill, NC 27599-7400, USA. E-mail: David_savitz{at}unc.edu

Sir—The relation of perinatal health to child health was addressed by Gissler et al.1 using unique data resources in Finland. The Medical Birth Register allowed them to study a cohort of over 60 000 births with virtually complete follow-up for most outcomes over a 7-year period. While they documented the expected increased mortality and long-term morbidity associated with being born early or small, they had an opportunity to examine effects of mild degrees of prematurity or small size but did not present the data to do so. Preterm birth, for example, is usually defined as birth prior to completion of 37 weeks' gestation, but in the obstetric community, births as early as 34 weeks are of little concern and births of 35 or 36 weeks are considered normal. Similarly, infants below 2500 g at birth are defined as low birthweight, but there is a widely held view that births as low as 2000 g are of little or no concern.

This perception is valid, in part at least, because modest degrees of prematurity or small size have limited adverse consequences for short-term survival, though there is still a measurable increase in mortality as late as 36 weeks' gestation (US National Center for Health Statistics, personal communication). The question of whether there are long-term, subtle adverse health effects associated with marginally early or small births is an important and unresolved public health question. Many intervention trials evaluate such endpoints as preterm birth but not severe preterm birth,2 and the large number of marginally preterm or low birthweight infants may result in sizeable impact on a population basis even if the increments in risk are modest. Therefore, the question of whether mild degrees of prematurity or reduced size are worthy of concern is critical, and the only way to address that issue is in studies of large populations of births with long-term follow-up of outcomes more sensitive than death alone.

Gissler et al.1 present data on gestational age grouped as 22–27, 28–36, and 37–44 weeks, but stratification within the 28–36 week group would be necessary to answer the question of what degree of prematurity incurs increased risk. Similarly, dividing the birthweight interval of 1500–2499 g into two groups, 1500–1999, 2000–2499 would be informative. If there are truly no measurable adverse consequences to being born at the margins of prematurity or low birthweight, the standards should be revised. If there are adverse sequelae, even if delayed and subtle, clinicians would need to take those risks into account as they make decisions about delivering infants early for medical indications.

References

1 Gissler M, Järvelin M-J, Louhiala P, Rahkonen O, Hemminki E. Can children's health be predicted by perinatal health? Int J Epidemiol 1999;28:276–80.[Abstract]

2 Hauth JC, Goldenberg RL, Andrews WW, DuBard MB, Copper RL. Reduced incidence of preterm delivery with metronidazole and erythromycin in women with bacterial vaginosis. N Engl J Med 1985; 333:1732–36.[Abstract/Free Full Text]


 

Authors' Response

Mika Gissler, Marjo-Riitta Järvelin, Pekka Louhiala, Ossi Rahkonen and Elina Hemminki

WHO Regional Office for Europe, 8 Scherfigsvej, DK-2100 Copenhagen, Denmark. E-mail: mgi{at}who.dk

Sir—We thank Professor Savitz for his valuable comment. As he stated, the group of newborns with gestational age from 28 to 36 weeks or with a birthweight from 1500 to 2499 g is heterogeneous, as our data1 confirm (Table 1Go). Detailed analysis of perinatal indicators shows that the mortality up to 7 years declined up to 34 gestational weeks and the cumulative incidence of long-term morbidity up to 41 weeks (Figure 1Go). In terms of birthweight, the optimum was reached at 3500 g (Figure 2Go). The relative changes by gestational age and birthweight are larger for mortality than for morbidity. The groups with gestational age from 33 to 36 weeks and/or a birthweight of 2500 g or more, which have been said to be of little or no concern in the obstetric community, do have increased long-term morbidity, even though they may not have any immediate health complications after birth.


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Table 1 Mortality and the cumulative incidence of long-term morbidity for children surviving perinatal period in some subgroups, Finnish 1987 cohort (No. = 60 254), %
 


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Figure 1 Long-term mortality and morbidity up to age of 7 years according to gestational age, %

 


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Figure 2 Long-term mortality and morbidity up to age of 7 years according to birthweight, %

 
When using birthweight and gestational age in longitudinal studies as confounders—for example when comparing health in different social classes2 or between sexes3—the best way to avoid problems with insufficient or questionable stratification is to use them as continuous variables.

References

1 Gissler M, Järvelin M-R, Louhiala P, Rahkonen O, Hemminki E. Can children's health be predicted by perinatal health? Int J Epidemiol 1999;28:276–80.[Abstract]

2 Gissler M, Rahkonen O, Järvelin M-R, Hemminki E. Social class differences in health until the age of seven years among the Finnish 1987 birth cohort. Soc Sci Med 1998;46:1543–52.[ISI][Medline]

3 Gissler M, Järvelin M-R, Louhiala P, Hemminki E. Boys have more health problems in childhood than girls—Follow-up of the 1987 Finnish birth cohort. Acta Paediatr 1999;88:310–14.[ISI][Medline]





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