Are babies getting bigger? Secular trends in fetal growth in Israel - A retrospective hospital-based cohort study

Background: A paradoxical secular trend of an increase in preterm births and a decrease in low birth weights has been reported in many developed countries over the last 25 years. Objective: To determine if this trend is true for Israeli neonates, and to add new information on secular trends in crown-heel length and head circumference. Methods: A hospital-based historic cohort design was used. Anthropometric data for 32,062 infants born at Rabin Medical Center in 1986-1987, 1994-1996, and 2003-2004 were collected from the hospital's computerized registry and compared over time for absolute values and proportional trends. Results: For the whole sample (gestational age 24-44 weeks) there was a significant increase in mean birth weight (by 41 g), crown-heel length (by 1.3 cm), and head circumference (by 0.1 cm) from 1986 to 2004 (P<0.001). A similar trend was found on separate analysis of the post-term babies. Term infants showed an increase in mean length and head circumference (P<0.001), but not weight, and moderately preterm infants (33-36 weeks) showed an increase in mean weight (81 g, P<0.001) and mean length (1.0 cm, P<0.001), but not head circumference. The proportion of post-term (42-44 weeks), preterm (24-36 weeks), very preterm (29-32 weeks), extremely preterm (24-28 weeks), low birth weight (< 2500 g) and very low birth weight (< 1500 g) infants decreased steadily and significantly over time (P<0.002). Conclusions: Babies born in our facility, term and preterm, are getting bigger and taller. This increase is apparently associated with a drop (not a rise) in the proportion of preterm infants. These results might reflect improvements in antenatal care and maternal determinants.