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Guest Editorial
Small Packages Victoria Allen, MD, MSc, FRCSC Deputy Editor
E
stablishing the expected date of confinement is one of the first and most important steps in the care of a pregnant woman. It usually starts with knowledge of the first day of the last normal menstrual period, in conjunction with other relevant history. Naegele’s rule (described in the 1800s) assumes a menstrual cycle length of 28 days with ovulation at 14 days, and adds one year, subtracts three months, and adds seven days to the last normal menstrual period to derive the expected date of confinement. Gestation wheels or electronic calculators, in the form of computer software, web-based online programs, or applications designed for smartphones, improve on Naegele’s rule by accounting for differences in the length of specific months, and may also be adjusted for differences in cycle length and information related to timing of assisted reproductive technology. The accuracy of such tools should be confirmed: wheels may not be balanced and calculators may have intrinsic arithmetic errors. Pelvic or abdominal palpation adds to the clinical assessment of gestational age.
Obstetrical ultrasound assessment (beginning in the 1970s) in the first trimester of pregnancy is useful for establishing or confirming expected date of confinement when menstrual dating is uncertain or discordant with physical examination. Ultrasound measurement error may be related to clinical characteristics such as gestational age and maternal body mass index, and technical issues such as operator experience, equipment quality, and the use of transabdominal or transvaginal imaging. Ultrasound assessment of gestational age in the first trimester can influence the number of pregnancies continuing beyond 42 weeks’ gestation1 (as well as other outcomes), although the risk of low birth weight increases with the magnitude of the difference between menstrual-based and early ultrasound-based gestational age estimates.2 While resources for screening for Down syndrome in pregnancy vary across Canada, the increasing availability of screening
J Obstet Gynaecol Can 2012;34(1):11–13
options that include a nuchal translucency measurement and crown rump length measurement (performed between 11 and 14 weeks gestation) should continue to improve the number of pregnancies with accurate determination of gestational age. The use of ultrasound for the determination or confirmation of gestational age in the second or third trimester is associated with increased measurement error and decreased accuracy. Fetal measurements are compared with age-specific references using standard formulas, and those formulas proposed by Hadlock, employing a combination of biparietal diameter, head circumference, abdominal circumference and femur length measurements demonstrate the most consistency across studies.3 Postnatal assessment of gestational age relies on external physical features of the newborn (described in the 1960s and includes creases on the sole of the foot, size of the breast nodule, nature of the hair, cartilaginous development of the earlobe, and in male infants testicular descent and scrotal rugae). These features begin to differentiate around 36 weeks gestational age, and should be independent of failure of growth potential.4 Application of this information—and the addition of neuromuscular components to the examination—forms the basis of the standardized New Ballard and the Dubowitz maturational scores, the most commonly used newborn assessment tools for the estimation of gestational age. Newborn clinical assessment has been shown to be the least precise dating method, with overestimation of gestation in infants born < 40 weeks and underestimation of gestation in those born ≥ 40 weeks, compared with ultrasound dating.5 A newly developed estimation of gestational age algorithm incorporates date of conception (if known), last normal menstrual period, fetal ultrasound dating, and physical examination of the newborn.6 It is currently available for use by established perinatal databases across Canada, and it provides a consistent method for dating pregnancies, allowing comparisons of pregnancy outcomes between provinces. Plans for application software designed for use with smartphones are underway. JANUARY JOGC JANVIER 2012 l 11
Guest Editorial
The size of the fetus may be estimated by palpation of the maternal abdomen using symphysis-fundal height, measured in centimetres from the top of the pubic bone to the top of the uterus, and should match the gestational age in weeks within 1 to 3 cm (after 20 weeks’ gestation). Symphysis-fundal height measurements may be influenced by multiple gestation, uterine fibroids, and maternal BMI, among other factors, and have poor sensitivity, high false positives and significant inter-and intra-observer variability. Ultrasound estimation of fetal weight may be used to resolve discrepancies between actual and expected symphysisfundal height measurements for suspected small or large for gestational age fetuses, or when symphysis-fundal height screening is not informative (as above), although the possibility of bias and precision of the formula in the population being assessed must be considered.7 Serial ultrasounds, incorporating carefully assigned gestational age and carefully measured fetal weight, performed longitudinally provide important information on fetal growth. Classification of fetal growth by estimation of fetal weight or birth weight alone is not sufficient when considering the influence of growth on adverse perinatal outcomes. An estimated weight threshold relative to a specific gestational age provides more relevant information about the prognosis associated with fetal growth abnormalities. Small for gestational age (SGA) may be described by thresholds of centiles (for example, 3rd or 10th) or standard deviations below the population average (for example, 1.0 or 2.0). The use of varying definitions is only one of the challenges in comparing the abundant literature evaluating etiologies, predictive factors, diagnostic and management options, and perinatal outcomes in fetuses with growth abnormalities. Customized birth weight or ultrasound estimation of fetal weight charts for gestational age standards have been proposed as a more reliable alternative for the diagnosis of SGA by taking account of physiological variables known to affect birth weight and postnatal growth (such as BMI, parity, ethnicity, and infant sex), and may reduce the number of pregnancies falsely identified as SGA. They are limited by the characteristics of the population with which they were developed and may not be applicable in all clinical situations, such as multiple gestation.8,9 Application of these programs to other populations should be validated before use and change of practice. Emerging modifications to standard growth curves include the addition of 3-D components to established sonographic measurements. So what do we know about the influence of small size on outcome? References within classical literature are rich with the use of smallness in the exploration of themes 12 l JANUARY JOGC JANVIER 2012
related to identity and mortality. Gulliver encounters the small citizens of Lilliput while documenting his travels through the societal upheaval of the time. Seven dwarfs are instrumental in helping Snow White regain a sense of self. Alice, in her adventures in Wonderland, cycles between being small and large, leading to adaptability and maturity. The child Huckleberry Finn travels along a river of selfdiscovery in a politically charged era in North American history. There are countless other examples. In medicine, fetuses with intrauterine growth restriction (IUGR) are a sub-population of small-for-gestational age fetuses, indicating the presence of a pathophysiologic process occurring in utero that inhibits fetal growth, with important implications for fetal and postnatal health. Outcomes associated with IUGR, including increased risks for perinatal morbidity and mortality, are influenced by timing of diagnosis, etiology and management. In this issue of JOGC, Andrea Lausman and colleagues provide a comprehensive summary of the identification, screening and management of IUGR, including a discussion of potential etiologies influenced by maternal, fetal, environmental, and placental factors.10 Clinical, ultrasonographic and biochemical screening components for the prediction of IUGR, including serial fetal assessment, antenatal placental examination, and maternal and fetal Doppler velocimetry, are discussed in detail. The authors further address fetal surveillance appropriate for the complex etiologies associated with IUGR, and comment on timing and mode of delivery designed to optimize perinatal outcomes. This information is useful in counselling a woman and her family regarding pregnancy options, planning investigations, arranging appropriate fetal surveillance, and providing appropriate newborn care. Information obtained from newborn examination and investigations and postnatal placental examination may predict recurrence and suggest pre-conception and other interventions in subsequent pregnancies. Long-term health problems of an infant born with growth restriction will be dependent on etiology and clinicians should take them into account when counselling prenatally regarding options for pregnancy care and surveillance and timing of delivery. Early studies evaluating the relationship of low birth weight to metabolic and cardiovascular disease later in life are limited by recall bias, frequently unreliable birth weight data, underestimation of preterm birth, and confounding factors such as social class. Some clues to later health concerns related to fetal growth abnormalities may possibly be derived from the Hongerwinter (the Dutch Famine of 1944–1945). The mass famine in this industrialized population affected people
Small Packages
of all social classes, and then was followed by almost universal prosperity in the post-war period. Observations suggest that timing of nutritional restriction in pregnancy may affect subsequent birth weight, while still contributing to later adverse health outcomes such as obesity and cardiovascular issues. There is also evidence for effects of nutritional deprivation in utero on age-associated decline of cognitive functions.11 Despite ongoing advances in obstetrical and neonatal care, Dr Lausman’s review emphasizes the substantial gaps remaining in the understanding of the complicated etiology and pathophysiology of intrauterine growth restriction, and encourages continued efforts to clarify this important disorder. Clearly, rigorously designed studies in the evaluation of the consequences of growth abnormalities in utero are critical if women and families with pregnancies affected with IUGR are to be provided with comprehensive and accurate information regarding short- and long-term prognosis. REFERENCES 1. Delaney M, Roggensack A; SOGC Clinical Practice Obstetrics Committee. Guidelines for the management of pregnancy at 41+0 to 42+0 Weeks. SOGC Clinical Practice Guideline No. 214, September 2008. J Obstet Gynaecol Can 2008;30:800–10.
2. Morin I, Morin L, Zhang X, Platt RW, Blondel B, Bréart G, et al. Determinants and consequences in menstrual and ultrasonographic gestational age estimates. BJOG 2005;112;145–52. 3. Chervenak FA, Skupski DW, Romero R, Myers MK, Smith-Levitin M, Rosenwaks Z, et al. How accurate is fetal biometry in the assessment of fetal age? Am J Obstet Gynecol 1998;178:678–87. 4. Usher R, McLean F, Scott KE. Judgment of fetal age. II. Clinical significance of gestational age and an objective measure for its assessment. Pediatr Clin North Am 1966;13:835–62. 5. Lynch CD, Zhang J. The research implications of the selection of a gestational age estimation method. Paediatr Perinat Epidemiol 2007;21:86–96. 6. Algorithm for the Estimation of Gestational Age, Canadian Perinatal Surveillance System. Ottawa: Public Health Agency of Canada; 2010. 7. Dudley, NJ. A systematic review of the ultrasound estimation of fetal weight. Ultrasound Obstet Gynecol 2005;25:80–9. 8. Joseph KS, Wilkins R, Dodds L, Allen VM, Ohlsson A, Marcoux S, et al. Customized birth weight for gestational age standards for males and females but not for blacks and whites. BMC Pregnancy Childbirth 2005;5:3. 9. Joseph KS, Fahey J, Platt RW, Liston RM, Lee SK, Suave R, e al. An outcome-based approach for the creation of fetal growth standards: do singletons and twins need separate standards? Am J Epidemiol 2009;169:616–24. 10. Lausman A, McCarthy FP, Walker M, Kingdom J. Screening, diagnosis, and management of intrauterine growth restriction. J Obstet Gynaecol Can 2012;34:17–28. 11. Schulz LC. The Dutch Hunger Winter and the developmental origins of health and disease. Proc National Acad Sci 2010;107:16757–8.
JANUARY JOGC JANVIER 2012 l 13
Small Packages Victoria Allen, MD, MSc, FRCSC Deputy Editor
E
stablishing the expected date of confinement is one of the first and most important steps in the care of a pregnant woman. It usually starts with knowledge of the first day of the last normal menstrual period, in conjunction with other relevant history. Naegele’s rule (described in the 1800s) assumes a menstrual cycle length of 28 days with ovulation at 14 days, and adds one year, subtracts three months, and adds seven days to the last normal menstrual period to derive the expected date of confinement. Gestation wheels or electronic calculators, in the form of computer software, web-based online programs, or applications designed for smartphones, improve on Naegele’s rule by accounting for differences in the length of specific months, and may also be adjusted for differences in cycle length and information related to timing of assisted reproductive technology. The accuracy of such tools should be confirmed: wheels may not be balanced and calculators may have intrinsic arithmetic errors. Pelvic or abdominal palpation adds to the clinical assessment of gestational age.
Obstetrical ultrasound assessment (beginning in the 1970s) in the first trimester of pregnancy is useful for establishing or confirming expected date of confinement when menstrual dating is uncertain or discordant with physical examination. Ultrasound measurement error may be related to clinical characteristics such as gestational age and maternal body mass index, and technical issues such as operator experience, equipment quality, and the use of transabdominal or transvaginal imaging. Ultrasound assessment of gestational age in the first trimester can influence the number of pregnancies continuing beyond 42 weeks’ gestation1 (as well as other outcomes), although the risk of low birth weight increases with the magnitude of the difference between menstrual-based and early ultrasound-based gestational age estimates.2 While resources for screening for Down syndrome in pregnancy vary across Canada, the increasing availability of screening
J Obstet Gynaecol Can 2012;34(1):11–13
options that include a nuchal translucency measurement and crown rump length measurement (performed between 11 and 14 weeks gestation) should continue to improve the number of pregnancies with accurate determination of gestational age. The use of ultrasound for the determination or confirmation of gestational age in the second or third trimester is associated with increased measurement error and decreased accuracy. Fetal measurements are compared with age-specific references using standard formulas, and those formulas proposed by Hadlock, employing a combination of biparietal diameter, head circumference, abdominal circumference and femur length measurements demonstrate the most consistency across studies.3 Postnatal assessment of gestational age relies on external physical features of the newborn (described in the 1960s and includes creases on the sole of the foot, size of the breast nodule, nature of the hair, cartilaginous development of the earlobe, and in male infants testicular descent and scrotal rugae). These features begin to differentiate around 36 weeks gestational age, and should be independent of failure of growth potential.4 Application of this information—and the addition of neuromuscular components to the examination—forms the basis of the standardized New Ballard and the Dubowitz maturational scores, the most commonly used newborn assessment tools for the estimation of gestational age. Newborn clinical assessment has been shown to be the least precise dating method, with overestimation of gestation in infants born < 40 weeks and underestimation of gestation in those born ≥ 40 weeks, compared with ultrasound dating.5 A newly developed estimation of gestational age algorithm incorporates date of conception (if known), last normal menstrual period, fetal ultrasound dating, and physical examination of the newborn.6 It is currently available for use by established perinatal databases across Canada, and it provides a consistent method for dating pregnancies, allowing comparisons of pregnancy outcomes between provinces. Plans for application software designed for use with smartphones are underway. JANUARY JOGC JANVIER 2012 l 11
Guest Editorial
The size of the fetus may be estimated by palpation of the maternal abdomen using symphysis-fundal height, measured in centimetres from the top of the pubic bone to the top of the uterus, and should match the gestational age in weeks within 1 to 3 cm (after 20 weeks’ gestation). Symphysis-fundal height measurements may be influenced by multiple gestation, uterine fibroids, and maternal BMI, among other factors, and have poor sensitivity, high false positives and significant inter-and intra-observer variability. Ultrasound estimation of fetal weight may be used to resolve discrepancies between actual and expected symphysisfundal height measurements for suspected small or large for gestational age fetuses, or when symphysis-fundal height screening is not informative (as above), although the possibility of bias and precision of the formula in the population being assessed must be considered.7 Serial ultrasounds, incorporating carefully assigned gestational age and carefully measured fetal weight, performed longitudinally provide important information on fetal growth. Classification of fetal growth by estimation of fetal weight or birth weight alone is not sufficient when considering the influence of growth on adverse perinatal outcomes. An estimated weight threshold relative to a specific gestational age provides more relevant information about the prognosis associated with fetal growth abnormalities. Small for gestational age (SGA) may be described by thresholds of centiles (for example, 3rd or 10th) or standard deviations below the population average (for example, 1.0 or 2.0). The use of varying definitions is only one of the challenges in comparing the abundant literature evaluating etiologies, predictive factors, diagnostic and management options, and perinatal outcomes in fetuses with growth abnormalities. Customized birth weight or ultrasound estimation of fetal weight charts for gestational age standards have been proposed as a more reliable alternative for the diagnosis of SGA by taking account of physiological variables known to affect birth weight and postnatal growth (such as BMI, parity, ethnicity, and infant sex), and may reduce the number of pregnancies falsely identified as SGA. They are limited by the characteristics of the population with which they were developed and may not be applicable in all clinical situations, such as multiple gestation.8,9 Application of these programs to other populations should be validated before use and change of practice. Emerging modifications to standard growth curves include the addition of 3-D components to established sonographic measurements. So what do we know about the influence of small size on outcome? References within classical literature are rich with the use of smallness in the exploration of themes 12 l JANUARY JOGC JANVIER 2012
related to identity and mortality. Gulliver encounters the small citizens of Lilliput while documenting his travels through the societal upheaval of the time. Seven dwarfs are instrumental in helping Snow White regain a sense of self. Alice, in her adventures in Wonderland, cycles between being small and large, leading to adaptability and maturity. The child Huckleberry Finn travels along a river of selfdiscovery in a politically charged era in North American history. There are countless other examples. In medicine, fetuses with intrauterine growth restriction (IUGR) are a sub-population of small-for-gestational age fetuses, indicating the presence of a pathophysiologic process occurring in utero that inhibits fetal growth, with important implications for fetal and postnatal health. Outcomes associated with IUGR, including increased risks for perinatal morbidity and mortality, are influenced by timing of diagnosis, etiology and management. In this issue of JOGC, Andrea Lausman and colleagues provide a comprehensive summary of the identification, screening and management of IUGR, including a discussion of potential etiologies influenced by maternal, fetal, environmental, and placental factors.10 Clinical, ultrasonographic and biochemical screening components for the prediction of IUGR, including serial fetal assessment, antenatal placental examination, and maternal and fetal Doppler velocimetry, are discussed in detail. The authors further address fetal surveillance appropriate for the complex etiologies associated with IUGR, and comment on timing and mode of delivery designed to optimize perinatal outcomes. This information is useful in counselling a woman and her family regarding pregnancy options, planning investigations, arranging appropriate fetal surveillance, and providing appropriate newborn care. Information obtained from newborn examination and investigations and postnatal placental examination may predict recurrence and suggest pre-conception and other interventions in subsequent pregnancies. Long-term health problems of an infant born with growth restriction will be dependent on etiology and clinicians should take them into account when counselling prenatally regarding options for pregnancy care and surveillance and timing of delivery. Early studies evaluating the relationship of low birth weight to metabolic and cardiovascular disease later in life are limited by recall bias, frequently unreliable birth weight data, underestimation of preterm birth, and confounding factors such as social class. Some clues to later health concerns related to fetal growth abnormalities may possibly be derived from the Hongerwinter (the Dutch Famine of 1944–1945). The mass famine in this industrialized population affected people
Small Packages
of all social classes, and then was followed by almost universal prosperity in the post-war period. Observations suggest that timing of nutritional restriction in pregnancy may affect subsequent birth weight, while still contributing to later adverse health outcomes such as obesity and cardiovascular issues. There is also evidence for effects of nutritional deprivation in utero on age-associated decline of cognitive functions.11 Despite ongoing advances in obstetrical and neonatal care, Dr Lausman’s review emphasizes the substantial gaps remaining in the understanding of the complicated etiology and pathophysiology of intrauterine growth restriction, and encourages continued efforts to clarify this important disorder. Clearly, rigorously designed studies in the evaluation of the consequences of growth abnormalities in utero are critical if women and families with pregnancies affected with IUGR are to be provided with comprehensive and accurate information regarding short- and long-term prognosis. REFERENCES 1. Delaney M, Roggensack A; SOGC Clinical Practice Obstetrics Committee. Guidelines for the management of pregnancy at 41+0 to 42+0 Weeks. SOGC Clinical Practice Guideline No. 214, September 2008. J Obstet Gynaecol Can 2008;30:800–10.
2. Morin I, Morin L, Zhang X, Platt RW, Blondel B, Bréart G, et al. Determinants and consequences in menstrual and ultrasonographic gestational age estimates. BJOG 2005;112;145–52. 3. Chervenak FA, Skupski DW, Romero R, Myers MK, Smith-Levitin M, Rosenwaks Z, et al. How accurate is fetal biometry in the assessment of fetal age? Am J Obstet Gynecol 1998;178:678–87. 4. Usher R, McLean F, Scott KE. Judgment of fetal age. II. Clinical significance of gestational age and an objective measure for its assessment. Pediatr Clin North Am 1966;13:835–62. 5. Lynch CD, Zhang J. The research implications of the selection of a gestational age estimation method. Paediatr Perinat Epidemiol 2007;21:86–96. 6. Algorithm for the Estimation of Gestational Age, Canadian Perinatal Surveillance System. Ottawa: Public Health Agency of Canada; 2010. 7. Dudley, NJ. A systematic review of the ultrasound estimation of fetal weight. Ultrasound Obstet Gynecol 2005;25:80–9. 8. Joseph KS, Wilkins R, Dodds L, Allen VM, Ohlsson A, Marcoux S, et al. Customized birth weight for gestational age standards for males and females but not for blacks and whites. BMC Pregnancy Childbirth 2005;5:3. 9. Joseph KS, Fahey J, Platt RW, Liston RM, Lee SK, Suave R, e al. An outcome-based approach for the creation of fetal growth standards: do singletons and twins need separate standards? Am J Epidemiol 2009;169:616–24. 10. Lausman A, McCarthy FP, Walker M, Kingdom J. Screening, diagnosis, and management of intrauterine growth restriction. J Obstet Gynaecol Can 2012;34:17–28. 11. Schulz LC. The Dutch Hunger Winter and the developmental origins of health and disease. Proc National Acad Sci 2010;107:16757–8.
JANUARY JOGC JANVIER 2012 l 13