Assessment of fetal growth

Normal fetal growth is a logarithmic process, marked by rapid mitosis at its early stages and by cellular hypertrophy and the accumulation of fat, glycogen, and connective tissue later in gestation. Growth-retarding influences can alter cell number, with a symmetric pattern of IUGR resulting if they occur early. Later insults, the result of uteroplacental compromise, affect cell size and may cause an asymmetric growth retardation. Fetuses with asymmetric growth retardation are at particular risk for intrauterine fetal demise and fetal distress in labor. The assessment of fetal growth is complicated by a lack of clear definition for what constitutes normality. Fetal growth curves should be derived from uncomplicated pregnancies. Separate curves should be available on the basis of multiple gestation and sex, maternal parity, and ethnic-racial grouping. Correction factors for maternal height and prepregnancy weight as well as sibling size at birth would be useful. Birth weight-derived data are suspect for preterm gestations; sonographic fetal weight curves may improve accuracy. Without sensitive epidemiologic growth assessment, other modalities (clinical, biochemical, and sonographic) will have limited usefulness. The assessment of fetal growth may include clinical means but care must be taken to garner a meticulous history and to record precisely serial fundal height. Many biochemical methods have been proposed for the detection of IUGR but they have a limited role as screening tests. Ultrasound remains the best method for the diagnosis, characterization, and follow-up of IUGR. Ultrasonography allows for the precise estimation of fetal weight. The calculation of HC:AC ratios allows for characterization of the pattern of IUGR. Evaluation of amniotic fluid volume and placental grading as well as the search for congenital anomalies are helpful exercises. Doppler flow studies of uterine and fetal blood flow may provide an understanding of the cause and severity of the growth-retarding process. Finally, careful antenatal surveillance and judicious timing of delivery are required following the identification of IUGR. Delivery should be planned in concert with the neonatologist.