Tracking of fetal growth characteristics during different trimesters and the risks of adverse birth outcomes

Background: Fetal growth characteristics are used to identify influences of several maternal characteristics and to identify individuals at increased risk of adverse outcomes. The extent to which fetal growth characteristics track in different trimesters is not known. Methods: In a population-based prospective cohort study among 8636 pregnant women, we examined the extent to which fetal growth characteristics track, are influenced by maternal socio-demographic and lifestyle related determinants and are associated with birth outcomes. Fetal growth was assessed in each trimester and at birth. Results: Correlation coefficient between first-trimester crown-rump length and birth-weight was r = 0.12 9P-value < 0.05). Correlation coefficients for fetal-head circumference, 9femur) length and 9estimated) fetal weight ranged from r = 0.16 to r = 0.30 9all P-values < 0.05) between second trimester and birth and from r = 0.36 to r = 0.58 9all P-values < 0.05) between third trimester and birth, and were highest for 9estimated) fetal weight. Correlation coefficients for 9estimated) fetal weight tended to be lower among overweight mothers, as compared with normal weight mothers, but were not influenced by other maternal characteristics. First, second and third-trimester fetal growth characteristics were associated with risks of preterm birth and small size for gestational age at birth, with the strongest associations present in third trimester. Conclusion: Fetal growth characteristics track moderately throughout gestation, with stronger tracking coefficients present in later pregnancy. Tracking coefficients were not materially influenced by maternal socio-demographic and lifestyle characteristics. First, second and third trimester fetal growth characteristics were associated with the risk of adverse birth outcomes.