Birth weight in live births and stillbirths.

OBJECTIVE: To establish a normal range of birth weights for gestational age at delivery and to compare the proportion of live births and stillbirths that are classified as small-for-gestational age (SGA) according to our normal range vs that of the INTERGROWTH-21st standard.

METHODS: The study population comprised 113 019 live births and 437 (0.4%) stillbirths. The inclusion criterion for establishing a normal range of birth weights for gestational age was the live birth of a phenotypically normal neonate ≥ 24 weeks' gestation and the exclusion criteria were smoking and prepregnancy hypertension, diabetes mellitus, systemic lupus erythematosus or antiphospholipid syndrome, pre-eclampsia, gestational hypertension, gestational diabetes mellitus or iatrogenic preterm birth for fetal growth restriction in the current pregnancy. Inclusion criteria were met by 92 018 live births. The proportions of live births and stillbirths with birth weights < 5th and < 10th percentiles of our normal range and those according to the INTERGROWTH-21st standard were determined and compared by the chi-square test and McNemar test.

RESULTS: The proportions of live births and stillbirths with a birth weight < 5th percentile according to our standard were significantly higher than and discordant with the proportion according to the INTERGROWTH-21st standard (live birth: 5.6% vs 3.4%; stillbirth: 37.2% vs 22.7%). Similarly, the proportion of live births and stillbirths with a birth weight < 10th percentile according to our standard were significantly higher than and discordant with those according to the INTERGROWTH-21st standard (live birth: 11.2% vs 6.9%; stillbirth: 44.3% vs 32.6%).

CONCLUSION: The INTERGROWTH-21st standard underestimates the proportion of SGA live births and stillbirths in our population. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.