Aspects of birth weight and its influencing variables

1.1. Data from 5,883 registering prenatal patients were used to examine variables influencing birth weight. Statistical handling by multiple linear regression techniques was confirmed by simple three-way cross-classification tables.2.2. Initial results indicated that maternal age, parity, weight, past history of having borne a baby in excess of 9 pounds, length of gestation, and sex of the infant were all of possible significance.3.3. Further analyses removing the overlapping effects of intercorrelated factors were made. Apparent influence of age and parity was then seen to result from parity only. Extension of these analyses indicated that the effect of parity was entirely due to the maternal prepregnant usual weight. Evidence of increasing gestational blood glucose levels seen with increases in maternal weight formed the basis for postulating an environmental cause for the relationship between maternal weight and infant birth weight.4.4. The significant effect of having previously borne a large baby, while in keeping with this postulated environmental cause since such persons have higher than average weights as well as blood glucose levels in pregnancy, in no way negates possible genetic explanations.5.5. Length of gestation has the greatest single effect on infant birth weight. Its use as an index of maturity is discussed in relation to the difficulties in applying results from group data with large variances to an individual.