Fetal growth restriction (FGR) is often the result of placental insufficiency and is characterized by insufficient transplacental transport of nutrients and oxygen. The main underlying entities of placental insufficiency, the pathophysiologic mechanism, can broadly be divided into impairments in blood flow and exchange capacity over the syncytiovascular membranes of the fetal placenta villi. Fetal growth restriction is not synonymous with small for gestational age and techniques to distinguish between both are needed. Placental insufficiency has significant associations with adverse pregnancy outcomes (perinatal mortality and morbidity). Even in apparently healthy survivors, altered fetal programming may lead to long-term neurodevelopmental and metabolic effects. Although the concept of fetal growth restriction is well appreciated in contemporary obstetrics, the appropriate detection of FGR remains an issue in clinical practice. Several approaches have aimed to improve detection, e.g., uniform definition of FGR, use of Doppler ultrasound profiles and use of growth trajectories by ultrasound fetal biometry. However, the role of placental morphometry (placental dimensions/shape and weight) deserves further exploration. This review article covers the clinical relevance of placental morphometry during pregnancy and at birth to help recognize fetuses who are growth restricted. The assessment has wide intra- and interindividual variability with various consequences. Previous studies have shown that a small placental surface area and low placental weight are associated with a slower growth of the fetus. Parameters such as placental surface area, placental volume and placental weight in relation to birth weight can help to identify FGR. In the future, a model including sophisticated antenatal placental morphometry may prove to be a clinically useful method for screening or diagnosing growth restricted fetuses, in order to provide optimal monitoring.
Background The clinical inability to correctly identify late fetal growth restriction (FGR) within a group of fetuses who are identified as small for gestational age (SGA) is an everyday problem for all obstetrician-gynecologists. This leads to substantial overtreatment of healthy small fetuses but also inadequate detection of the growth-restricted fetuses that may benefit from timely delivery. Redistribution of the fetal circulation, signaled by an abnormal ratio of the Doppler velocity flow profiles of the umbilical artery and the middle cerebral artery, more specifically an increased umbilicocerebral ratio (UCR) (or its inverse: a decreased cerebroplacental ratio (CPR)), is an adaptation to chronic hypoxemia and nutritional scarcity with long-term consequences in survivors. The relevance of an abnormal UCR has been signaled extensively, and there is a general consensus that it is a signal of FGR, independent of size, with a strong association with poor outcomes. Yet, in the current literature, no comparisons of a monitoring-delivery strategy based on unfavorable UCR have been published. The objective of the Doppler Ratio In fetal Growth restriction Intervention Trial At (near) Term (DRIGITAT) is to evaluate if the timing of the delivery based on an abnormal UCR in late preterm fetuses identified as SGA improves neurodevelopmental outcomes at 2 years of age. Methods The DRIGITAT study is a national multicenter cohort study of women with singleton pregnancies between 32 and 37 weeks of gestation identified as SGA, with a nested randomized controlled trial (RCT) in case of an abnormal UCR (> 0.8). Recruiting centers are in The Netherlands. In the nested RCT, women are randomized to either immediate induction of labor or expectant management from 34 weeks in case of severely abnormal size (EFW or FAC < p3) and from 36 weeks in case of mildly abnormal size (EFW or FAC p3–p10). The primary outcome measure is the 7-point average difference in the composite cognitive score (CCS) and composite motor score (CMS) on the Bayley-3 at 2 years. Secondary outcome measures include a composite outcome of neonatal morbidity, perinatal mortality, mode of delivery, maternal quality of life, costs, and predictive value of serum biomarkers. Analyses will be by intention to treat. The required sample size is determined for the nested RCT as 185 patients. Discussion This study will provide insight into the diagnostic efficacy of UCR measurement in the evaluation of SGA fetuses in order to differentiate the healthy SGA fetus from the growth-restricted fetus and to determine if a fetus with abnormal UCR benefits from early delivery. Trial registration Healthcare Evaluation Netherlands NTR6663. Registered on 14 August 2017.
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