When several factors are accounted for, stillbirth may be associated with both severely restricted and excessive fetal growth, according to a study by US researchers published in PLOS Medicine.
Radek Bukowski and colleagues from the NICHD Stillbirth Collaborative Research Network investigated the fetal growth abnormalities associated with stillbirth using a new approach developed by the Stillbirth Collaborative Research Network to estimate gestational age.
Using this approach the authors investigated all the stillbirths, and a sample of live births, which occurred over 2 and a half years at 59 hospitals in five US regions.
The authors found that overall, abnormal fetal growth was identified in 25% of stillbirths using population norms and in above 50% of stillbirths using ultrasound or individualized norms: Small for Gestational Age (SGA: the bottom 10% of the population weight for gestational age) was associated with a 3- to 4-fold increased risk of stillbirth compared to having a fetus with “appropriate” weight for gestational age based on all three norms. Large for Gestational Age (LGA: the top 10% of the population weight for gestational age) was associated with an increased risk of stillbirth based on the ultrasound and individualized norms but not the population norms. Being more severely SGA or LGA (below the 5th percentile or above the 95th percentile) was associated with an increased risk of stillbirth.
Although the accuracy of these findings is likely to be affected by aspects of the study design, these findings suggest that, contrary to current practices, strategies designed to prevent stillbirth should focus on identifying both severely SGA and severely LGA fetuses.
The authors say: “When accounting for time of death and using norms developed in normal pregnancies, both SGA and LGA birth weights were associated with stillbirth in our study.
They continue: “The association is mainly related to severe SGA and LGA pregnancies, with birth weights either below the 5th or above the 95th percentile. Thus, classifying 10% of pregnancies as abnormally grown has the potential to identify 44%-46% of future stillbirths.”
This work, including the design and conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review and approval of the manuscript, was supported by grant funding from the Eunice Kennedy Shriver National Institute of Child Health and Human Development: U10- HD045953 Brown University, Rhode Island; U10-HD045925 Emory University, Georgia; U10-HD045952 University of Texas Medical Branch at Galveston, Texas; U10- HDO45955 University of Texas Health Sciences Center at San Antonio, Texas; U10-HD045944 University of Utah Health Sciences Center, Utah; and U01-HD045954 RTI International, RTP. Program officers from the funding agency (UMR and MW) were members of the Steering Committee of the study, and contributed to the study design, management, interpretation of the data, as well as preparation, review and approval of the manuscript.
The authors have declared that no competing interests exist.
Fetal Growth and Risk of Stillbirth: A Population-Based Case-Control Study. Bukowski R, Hansen NI, Willinger M, Reddy UM, Parker CB, et al. PLoS Med 11(4): e1001633. doi:10.1371/journal.pmed.1001633, published online 22 April 2014.