TENDENCY TO REPEAT GESTATIONAL-AGE AND BIRTH-WEIGHT IN SUCCESSIVE BIRTHS

This study is based on all 454,358 single births which occurred in Norway from 1967 through 1973. The results confirm and extend findings from earlier studies in terms of the tendency to repeat low-birth-weight and small- or large-for-gestational age (SGA or LGA) deliveries in subsequent births. The relative risk that the second birth will be SGA, given that the mother's first birth was SGA, is 3.4 among mothers who were delivered of their first and second infants during the 7 year period. Also, mothers with SGA first-born infants account for a 27.7% attributable risk of all SGA second births. Conversely, mothers of LGA first-born infants have a relative risk of 3.0 of repeating a LGA second birth, and in addition, these mothers account for an attributable risk of 21.2% of all LGA second births. Similar results are shown for repeated outcomes such as preterm, post-term, low-weight, and high-weight births. The study also demonstrates a cumulative risk for any of these outcomes in the third birth, given that both of the first two births were of similar outcome. Thus, it is suggested that there are intrinsic factors which are responsible for this tendency to produce births with similar gestational age and birth weight. An association between complications during pregnancy or delivery and low birth weight, or other known risk factors which predispose for a similar pregnancy outcome, are unable to account for these data on successive births. © 1979.