You are in: eMedicine Specialties > Radiology > OBSTETRICS/GYNECOLOGY Intrauterine Growth RetardationArticle Last Updated: Dec 28, 2006AUTHOR AND EDITOR INFORMATIONSection 1 of 6
  Author: Vikram S Dogra, MD, Professor of Diagnostic Radiology, University of Rochester School of Medicine; Director, Division of Ultrasound, Associate Chair of Education and Research, Department of Imaging Sciences, University of Rochester Medical Center Vikram S Dogra is a member of the following medical societies: American College of Radiology, American Institute of Ultrasound in Medicine, American Roentgen Ray Society, Association of Program Directors in Radiology, Radiological Society of North America, Society of Radiologists in Ultrasound, and Society of Uroradiology Coauthor(s): Shweta Bhatt, MBBS, DMRD, Research Fellow, Department of Radiology, University Hospitals of Cleveland, Case Western Reserve University Editors: Christopher L Sistrom, MD, Associate Chair for Research, Assistant Professor, Department of Radiology, University of Florida School of Medicine; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Karen L Reuter, MD, FACR, Professor, Department of Radiology, Lahey Clinic Medical Center; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Eugene C Lin, MD, Consulting Staff, Department of Radiology, Virginia Mason Medical Center Author and Editor Disclosure Synonyms and related keywords: IUGR, intrauterine growth restriction, fetal growth, small for gestational age, asymmetric IUGR, symmetric IUGR, asymmetrical IUGR, symmetrical IUGR, growth-restricted fetus, transcerebellar diameter, head-sparing effect, abdominal circumference, head circumference, biparietal diameter, oligohydramnios INTRODUCTIONSection 2 of 6
  BackgroundThe term intrauterine growth restriction has largely replaced the term intrauterine growth retardation (IUGR). The definition of IUGR is a problematic one because we do not know the inherent growth potential of the fetus. The most common definition used is fetal weight below the 10th percentile for gestational age. In most cases of fetal growth restriction, the transcerebellar diameter appears to be spared and can be used as an unbiased measure of gestational age. The transcerebellar diameter in millimeters is equal to gestational age in weeks to 22 weeks of gestation. With this definition, IUGR and "small for gestational age" are synonymous terms. IUGR has a prevalence of 10% for all pregnancies. However, the figure varies in different patient populations, with rates of 3-5% for healthy mothers and 25% or higher for some high-risk groups, such as hypertensive mothers. Growth-restricted pregnancies are often complicated by a high rate of antepartum and intrapartum fetal distress and the need for cesarean delivery. Infants who are small for their gestational dates are predisposed to low APGAR scores, low cord pH, intraventricular hemorrhage, necrotizing enterocolitis, hypoglycemia, hypocalcemia, and polycythemia. For excellent patient education resources, visit eMedicine's Pregnancy and Reproduction Center. PathophysiologyEtiology The causes of IUGR can be either fetal or maternal. Fetal causes of IUGR include aneuploidy, trisomy 13, trisomy 18, triploidy, intrauterine infection, cytomegaloviral infection, and toxoplasmosis. Maternal causes of IUGR include use of drugs (including recreational drugs such as marijuana), alcohol consumption, placental insufficiency, diabetes, late conception (possible cause), and a history of having a baby small for his or her age. Asymmetrical vs symmetrical IUGR In most cases of IUGR, especially those due to primary placental insufficiency, the fetal abdomen is small, but the head and extremities are normal or near normal. This finding is known as the head-sparing effect. In cases of severe, early-onset IUGR (those due to chromosomal anomalies), the fetus tends to be more symmetrically small. This condition leads to the existence of 2 distinct subgroups; however, these subgroups significantly overlap. Fetal villus circulation The placenta is the lifeline to the fetus, and when challenged, it has a remarkable ability to adapt. Developmental problems can occur from the maternal side, the fetal side, or both. To understand these problems, knowledge of the development and the physiology of the villus circulation is needed. In the first trimester, the endometrium is invaded by the mesenchymal villi, which are made up of trophoblast, stroma, and a core of vessels. Early in pregnancy, the mesenchymal villi transform into immature intermediate stem villi, which then differentiate into stem villi. The primary-, secondary-, and tertiary-stem villi form the scaffolding from which subsequent villi develop. The histologic structure of the terminal villi optimizes maternal-fetal transfer of nutrients and oxygen. Vascularization of the villi occurs in the first and second trimesters by the process of branching angiogenesis. Three basic theories regarding the mechanics of the placental circulation are described. As reported in one color Doppler investigation, the theory that best suits these findings is the Ramsey theory. In this mechanism, blood enters the intervillous spaces via the spiral arteries. While moving within the intervillous space, the maternal blood bathes the individual units, which are composed of a fetal arterial, venous, and capillary network. The maternal blood then leaves the intervillous space by the draining basal veins. The transfer of oxygen and nutrients occurs at the interface between the terminal and intermediate mature villi and the intervillous space. Oxygen and nutrients enter the fetal villous venous circulation and are transferred to the fetus via the umbilical cord. Kingdom et al demonstrated that maldevelopment of the villus tree in pregnancies complicated by fetal growth restriction is associated with abnormal uterine artery waveforms, which are Doppler findings indicating abnormal uteroplacental blood flow. In pregnancies also complicated by absent end-diastolic umbilical flow, the placental villi are elongated, and the capillary loops are uncoiled and sparse. These findings are correlated with an increase in fetal-placental vascular impedance and impair gas and nutrient exchange. An enhanced branching angiogenesis represents an adaptive response to impaired uteroplacental blood flow. FrequencyUnited StatesBy definition, the prevalence of IUGR is 10%; fetuses with an estimated weight of less than 10% for gestational age are defined as being growth restricted. Mortality/MorbidityThe perinatal mortality for infants with IUGR is 6-10 times greater than that of a normal-growth population. IUGR is a major cause of intrapartum fetal distress, intrapartum asphyxia, hypoglycemia, hypocalcemia, meconium aspiration, and intrauterine demise. SexThis condition affects only pregnant women. AgeThe incidence of IUGR increases with increasing maternal age. Clinical DetailsIUGR is usually related to preeclampsia. Preferred ExaminationThe preferred method for evaluating the IUGR is ultrasonographic examination. ULTRASOUNDSection 3 of 6
FindingsMethods of evaluation The triplex mode is used for the evaluation of the umbilical venous blood flow. This mode comprises color Doppler sonography of the umbilical vein, pulsed Doppler velocimetry, and real-time sonography to measure the diameter of the umbilical vein. Doppler study of the umbilical artery can be done anywhere along the length of the umbilical artery. One should try to obtain as vertical view as possible on the umbilical artery. Blood in the main uterine arteries flows in a direction opposite that in the iliac arteries. The typical waveform shows a deep notch in relation to the closure of the aortic valve. The notch that is present before pregnancy gradually disappears during pregnancy, and diastolic flow increases with advancing gestation (ie, the vessel resistance decreases). Diagnosis of IUGR Several clinical and sonographic parameters can be used in combination to establish the diagnosis of IUGR with greater certainty. The key parameters for diagnosing IUGR are (1) the estimated fetal weight, (2) the volume of amniotic fluid, and (3) the mother's blood pressure status. Sonographic criteria for IUGR The sonographic criteria for IUGR include (1) an elevated ratio of femoral length to abdominal circumference (AC), (2) an elevated ratio of head circumference (HC) to AC, and (3) unexplained oligohydramnios. The AC measurement is the best single measurement to assess fetal growth because, in growth curtailment, the liver is virtually always affected. Hadlock charts can be used to calculate the fetal weight from the AC. Most ultrasonography machines also use the Hadlock method of calculating fetal weight. The literature describes at least 47 formulas for the estimation of fetal weight. Using the Shepard formula (AC and biparietal diameter [BPD]), one can come within 5% of the true fetal weight and within 10% of the fetal weight 80% of the time. However, 20% of the time, the estimation of the fetal weight may be discrepant by more than 10%. Oligohydramnios is an indicator of IUGR. Amniotic fluid of less than 5 cm, as measured in the four quadrants, is suggestive of oligohydramnios. Other causes of oligohydramnios include death in utero, renal agenesis, and premature rupture of membranes. The rationale for performing a Doppler study in the diagnosis of IUGR is that many cases of growth restriction are thought to be associated with small vessel disease in the fetoplacental or uteroplacental circulation. Numerous Doppler criteria have been proposed for diagnosing IUGR. These involve at least 3 of the following waveform indices:
Abnormal findings on Doppler waveforms include the following:
An S/D ratio of greater than 3 after 30 weeks of gestation is abnormal. The reversal of flow in ductus venosus is suggestive of a fetus with severely compromised IUGR and reflects fetal metabolic acidemia. Umbilical blood flow Umbilical venous blood flow, both absolute flow (in mm/min) and corrected blood flow (in mL/min/kg) are reduced in IUGR. Presence of pulsations in umbilical vein waveform between 8 and 12 weeks is normal, and its persistence is abnormal. The presence of umbilical vein pulsations is associated with an increased risk of an adverse perinatal outcome. Degree of ConfidenceFetal weight below the 10th percentile has negative predictive value of 99%, a sensitivity of 89%, and a specificity of 88% for the detection of IUGR. An elevated HC-to-AC ratio has a negative predictive value of 98%, a sensitivity of 82%, and a specificity of 94% for the detection of IUGR. Decreased weight with decreased amniotic fluid and the presence of hypertension are good predictors of IUGR. INTERVENTIONSection 4 of 6
If a patient has an abnormal spectral Doppler tracing and if the suspicion for IUGR is high, the patient should be referred to a perinatologist for care. MULTIMEDIASection 5 of 6
REFERENCESSection 6 of 6
Intrauterine Growth Retardation excerpt Article Last Updated: Dec 28, 2006 | ||||||||||||||||||||||||||
