Repeater” studies – Development of a new research field

The tendency to repeat birth weight in successive birth was first published in 1977. The study was based on 81 400 mothers who had their first and second singleton birth within the study period 1967-73, based on information in the Medical Birth Registry of Norway. The paper was presented at a large NICHD (National Center of Child Health and Human Development, NIH) seminar focusing on preterm birth. This meeting started a creative, international long lasting collaboration, a series of papers and book chapters has been published. It seemed like mothers are programmed to give birth to babies of a certain size and age. And if they depart from this norm the baby is at an increased risk of mortality. Also, the tendency to repeat gestational age and birth weight exists across generations, with the same increased risk if the pattern is departed from. This means that if a mother who herself was of low birth weight give birth to a likewise small baby, then that baby has improved survival compared to a likewise small baby where the mother was relatively heavy. This effect across generations is also present on the paternal in addition to the maternal side. Recently the medical birth registration data set has provided possibilities to examine the effect of changing partners from one pregnancy to the next one. Also, half siblings (maternal and paternal) is another valuable data source to explore. Soon 3 generational repeater studies will become available as the first births in the registry by now become grandmothers and grandfathers.