Numerous ultrasound-based fetal weight references have been published since the early 1980s. 17 – 21 Consequently, a population birthweight reference will significantly under-diagnose SGA infants in preterm births. The 10 th percentile of the birthweight reference in preterm, for example, is substantially lower than the 10 th percentile of the ultrasound-based fetal weight reference. 9 – 17 Thus, their birthweight does not represent all fetuses in utero at a given gestational week in preterm. However, evidence has shown that infants born preterm are more likely to be growth-restricted. They provide birthweight percentiles by each gestational week. 3 – 8 These population references were developed with very large, mostly population-based databases. In most clinical and epidemiologic research, birthweight-for-gestational-age references have been commonly used. Commonly used population references and standards Thus, a standard may have more clinical utility than a population reference.ġ. Use of a population reference will yield a relative fetal size in relation to the total population, while a standard will assess a fetal size in comparison to normally-grown fetuses. When the population reference and the standard are applied to an individual fetus or infant, interpretation of the findings differs. On the other hand, a standard is usually based on low-risk pregnancies with a normal outcome. A population reference is often established based on a large sample size (ideally representing the underlying population) using a study population including both low-risk and high-risk pregnancies, and both normal and abnormal perinatal outcomes. Regardless of which percentile is applied, a reference or standard is required. 3 EFW or birthweight < 5 th or < 3 rd percentiles are also used. The purpose of this review is to summarize literature on the definition of abnormal fetal growth that go beyond simple fetal size.Ĭurrently, estimated fetal weight (EFW) or birthweight below the 10 th percentile of certain reference at a given gestational week is commonly defined as small for gestational age (SGA). As a result of this confusion, underintervention and overintervention can occur.” Therefore, an objective assessment of normal and abnormal fetal growth has enormous utility in prenatal and neonatal care and outcome-based research. Diagnosis and management are complicated by the use of ambiguous terminology and a lack of uniform diagnostic criteria…… Size alone is not an indication of a complication. The American College of Obstetricians and Gynecologists Practice Bulletin 2 states: “ Intrauterine growth restriction is one of the most common and complex problems in modern obstetrics. 1 However, the latter has not been clearly defined. Common adult diseases such as type 2 diabetes and cardiovascular conditions have been linked to abnormal fetal growth, particularly fetal growth restriction (FGR). Normal fetal growth is a critical component of a healthy pregnancy and influences the long-term health of the offspring. An improved definition of abnormal fetal growth should benefit both research and clinical practice. Although the concept of an integrated definition appears promising, further development and testing are required. Such a definition may incorporate fetal size with the status of placental health measured by maternal and fetal Doppler velocimetry and biomarkers, biophysical findings and genetics. The authors further discuss recent advances towards an integrated definition for fetal growth restriction. Pros and cons of different approaches to customize fetal growth standards are described. The authors review various references and standards that are widely used to evaluate fetal growth, and discuss common pitfalls of current definitions of abnormal fetal growth. However, defining normal and abnormal fetal growth has been a long-standing challenge in clinical practice and research.
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