Multicountry study identifies ideal standards for fetal growth

Using ultrasound data from more than 4000 pregnancies in women in 8 countries, researchers have identified ideal standards of fetal growth and development. The findings, published in The Lancet, represent benchmarks for clinical interpretation of routine ultrasound measurements across populations.

Funded by the Bill & Melinda Gates Foundation, the Fetal Growth Longitudinal Study (FGLS) was designed to develop international growth and size standards for fetuses from conception to birth. Ultrasound was used to take fetal anthropometric measurements in 4,321 women in Brazil, China, India, Italy, Kenya, Oman, the UK, and the United States. All of them had a reliable estimate of gestational age confirmed by ultrasound measurement of crown-rump length in the first trimester. The participants were from urban areas and environments ideal for healthy growth, given access to adequate nutrition, education, low environmental contaminants, and good health care.

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The researchers used ultrasound every 5 weeks from 14 weeks’ to 42 weeks’ gestation to take five primary measures of fetal growth: head circumference, biparietal diameter, occipitofrontal diameter, abdominal circumference, and femur length. Mean differences between the observed and smoothed centiles for the 3^rd, 50^th and 97^th centiles, respectively, were small: 2.25 mm (SD 3.0), 0.02 mm (3.0), and -2.69 mm (3.2) for head circumference; 0.83 mm (0.9), -0.05 mm (0.8), and -0.84 mm (1.0) for biparietal diameter; 0.63 mm (1.2), 0.04 mm (1.1), and -1.05 mm (1.3) for occipitofrontal diameter; 2.99 mm (3.1), 0.25 mm (3.2), and -4.22 mm (3.7) for abdominal circumference; and 0.62 mm (0.8), 0.03 mm (0.8), and -0.65 mm (0.8) for femur length. The international standards for fetal growth are represented by the researchers’ calculation of the 3^rd, 5^th, 10^th, 50^th, 90^th, 95^th and 97^th centile curves according to gestational age for the ultrasound measures. 

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