Table 11

 

      Table 11 presents live births by birth weight for as many years as possible between 1990 and 1998.

 

Description of variables: Birth weight of a live-born infant is defined as the weight determined immediately after delivery, and it should preferably be expressed in grams to a degree of significance which will allow classification by 500-gramme intervals to be made from 499 grams or less to 5 000 grams or more[1].

 

The birth weight classification used in this table is as follows: under 499 grams (500 grams or less), 500 gram intervals through 4 500-4 999 grams, 5 000 or more and unknown.  Where birth weight has been reported in ounces, it has been converted to grams using the factor of 28.3495.

 

Low-birth-weight infants are those weighing 2 500 grams or less[2], that is, those appearing in the first five categories of this table.

 

Reliability of data: Data from civil registers of live births which are reported as incomplete (less than 90 per cent completeness) or of unknown completeness are considered unreliable and are set in italics rather than in roman type.  Table 1 and the technical notes for the table provide more detailed information on the completeness of live-birth registration.  For more information about the quality of vital statistics data in general, and the information available on the basis of the completeness estimates in particular, see section 4.2 of the Technical Notes.

 

Limitations: Statistics on live births by birth weight are subject to the same qualifications which have been set forth for vital statistics in general and birth statistics in particular as discussed in section 4 of the Technical Notes.

 

The reliability of the data, an indication of which is described in the above paragraph is an important factor in considering the limitations.  In addition, some live births are tabulated by date of registration and not by date of occurrence; these have been indicated by a (+). Whenever the lag between the date of occurrence and date of registration is prolonged and, therefore, a large proportion of the live-birth registrations are delayed, birth statistics for any given year may be seriously affected.

 

Another factor that limits international comparability is the practice of some countries or areas not to include in live-birth statistics infants who were born alive but died before registration or within the first 24 hours of life, thus underestimating the total number of live births.  Statistics of this type are footnoted.

 

In addition, comparability may be impaired if weighing of the newborn infant is not prompt, if the scales are not accurate or if the weights are rounded, particularly in the case of those measured in pounds and ounces.  Birth weight, however, can be measured objectively given minimum equipment and, unlike some methods of estimating gestational age, it does not depend on memory.

 

Data on live births by birth weight and on live births by gestational age, the latter presented in table 12, are useful in the study of infant mortality because infants of low birth weight and those of curtailed gestation are subject to higher risks of mortality and morbidity[3].

 

The relatively limited coverage of this table is due to the fact that many countries or areas do not collect and tabulate data on birth weight.

 

Coverage: Live births by birth weight are shown for 66 countries or areas.

 

Earlier data: Live births by birth weight have been shown previously in issues of the Demographic Yearbook featuring natality.  For information on the years covered, readers should consult the Index.