New Definition of Fetal Growth Restriction: Consensus Regarding a Major Obstetric Complication.

Fetal growth restriction (FGR) affects 5–10% of all pregnancies, and it is the second leading cause of perinatal mortality, accounting for 30% of stillbirths; it leads to prematurebirths and intrapartum asphyxia.1 Fetuses with FGR have an increased risk for perinatal morbidity and mortality, impaired neurological and cognitive developmentduring childhood and adolescence, and cardiovascular and endocrine disorders in adulthood.2 Fetal growth restriction is characterized by cases wherein the fetus does not achieve full intrauterine growth and development because of impaired placental function.1 However, in clinical practice, FGR is difficult to define, and there is currently no gold standard for its diagnosis. One of the greatest challenges is the differentiation between small for gestational age (SGA) fetuses, who are constitutionally small and healthy, and restricted fetuses, who present with some degree of placental dysfunction and an increased risk for adverse perinatal outcomes.3 Inboth theliteratureandclinicalpractice,manyauthorsand medical schools use different concepts to define FGR on the basis of biometric factors (weight percentile), Doppler (umbilical artery, middle cerebral artery, uterine artery, and ductus venosus), and biochemical markers (primarily placental growth factor PlGF). In 2016, a multicenter team of international FGR experts conducted a study based on the Delphi method in an attempt to establish a consensus regarding the definition of early and late FGR.4 The study included questionnaires with four phases, and the results were reported to the participants after each phase. In thefirst phase, the distinction between early and late FGRwas defined. The second and third stages discussed the parameters that could be separately considered for diagnosing FGR and those that had to be considered along with other parameters to conclude a diagnosis. In thefinal stage, somepossible algorithmswere presented to experts, and the algorithmwith thehighest number of votes was considered the final algorithm for defining FGR.2 The consensus concluded that the cutoff value between early and late FGR would be gestational age (GA) of 32 weeks, and the followingparameterswereused todefineFGR in theabsenceof fetal malformations: early FGR (< 32 weeks): (i) fetal abdominal circumference below the third percentile for GA OR estimated fetal weight below the third percentile for GA OR zero diastole of the umbilical artery on Doppler (isolated criteria) and (ii) estimated fetal weight or waist circumference below the tenth percentile for GA AND the pulsatility index of the uterine and umbilical arteries above the 95th percentile for GA (combined parameters) and late FGR ( 32 weeks): (i) fetal abdominal circumference below the third percentile for GAOR estimated fetalweightbelow the thirdpercentile forGAand (ii) the combinationofat least twoof the followingparameters: (a) estimated fetalweight or fetal abdominal circumferencebelow the tenth percentile for GA, (b) the reduction ofmore than two quartiles in the growth curve, and (c) the cerebroplacental association below the fifth percentile for GA or the pulsatility index of the umbilical artery above the 95th percentile for GA. Establishing an accurate diagnosis of FGR is fundamental both in the obstetric clinic to improve the detection of fetuses at an increased risk for adverse perinatal outcomes, and in scientific investigations to standardize concepts and enable further discoveries. Although the consensus based on the Delphi method establishes definitions that appear appropriate and consistent with recent studies, we should remember that it is a consensus based only on expert opinion, which requires scientific evidence to be ratified.