eMedicine Specialties > Radiology > Obstetrics/Gynecology
Intrauterine Growth Retardation
Updated: Dec 28, 2006
Introduction
Background
The 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.
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Pathophysiology
Etiology
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.
Frequency
United States
By 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/Morbidity
The 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.
Sex
This condition affects only pregnant women.
Age
The incidence of IUGR increases with increasing maternal age.
Presentation
IUGR is usually related to preeclampsia.
Preferred Examination
The preferred method for evaluating the IUGR is ultrasonographic examination.
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| References |
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References
Benson CB, Doubilet PM, Saltzman DH. Intrauterine growth retardation: predictive value of US criteria for antenatal diagnosis. Radiology. Aug 1986;160(2):415-7. [Medline].
Bewley S, Cooper D, Campbell S. Doppler investigation of uteroplacental blood flow resistance in the second trimester: a screening study for pre-eclampsia and intrauterine growth retardation. Br J Obstet Gynaecol. Sep 1991;98(9):871-9. [Medline].
Bower S, Vyas S, Campbell S, Nicolaides KH. Color Doppler imaging of the uterine artery in pregnancy: normal ranges of impedance to blood flow, mean velocity and volume of flow. Ultrasound Obstet Gynecol. Jul 1 1992;2(4):261-5. [Medline].
Doubilet PM, Benson CB. Sonographic evaluation of intrauterine growth retardation. AJR Am J Roentgenol. Mar 1995;164(3):709-17. [Medline].
Hadlock FP, Harrist RB, Carpenter RJ. Sonographic estimation of fetal weight. The value of femur length in addition to head and abdomen measurements. Radiology. Feb 1984;150(2):535-40. [Medline].
Kingdom JC, Burrell SJ, Kaufmann P. Pathology and clinical implications of abnormal umbilical artery Doppler waveforms. Ultrasound Obstet Gynecol. Apr 1997;9(4):271-86. [Medline].
Kurjak A, Azumendi G, Andonotopo W. Three- and four-dimensional ultrasonography for the structural and functional evaluation of the fetal face. Am J Obstet Gynecol. Sep 29 2006.
Lazebnik N, Lazebnik RS. Doppler Evaluation in intrauterine growth-restricted fetuses. In: Dogra VS, Rubens DJ, eds. Philadelphia, Pa: Hanley & Belfus; 2003:67-74.
Manning FA. The use of sonography in the evaluation of the high-risk pregnancy. Radiol Clin North Am. Jan 1990;28(1):205-16. [Medline].
Paspulati RM, Bhatt S, Nour S. Sonographic evaluation of first-trimester bleeding. Radiol Clin North Am. Mar 2004;42(2):297-314. [Medline].
Shepard MJ, Richards VA, Berkowitz FL. An evaluation of two equations for predicting fetal weight by ultrasound. Am J Obstet Gynecol. 1982;142:47.
Further Reading
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
