Fetal size and growth velocity in the prediction of intrapartum caesarean section for fetal distress

Fetal Growth and Adiposity of Infants Born Large for Gestational Age in Three Harmonized Randomized Trials

OBJECTIVE

 Infants born large for gestational age (LGA) are at an increased risk of short- and longer-term adverse outcomes. Understanding fetal growth and adiposity and their trajectories may help inform interventions to prevent birth of LGA infants. We aimed to compare fetal growth and adiposity measures of infants born LGA with those born not LGA, to determine whether the discrepancy at birth was primarily due to larger size throughout gestation, or instead to different trajectories of fetal growth.

STUDY DESIGN

 This was a secondary analysis of secondary outcomes of fetal growth and adiposity from three harmonized randomized trials-the LIMIT, GRoW, and Optimise randomized trials. These trials recruited women in early pregnancy, and a singleton gestation, from three major public metropolitan Adelaide maternity hospitals. Maternal body mass index (BMI) ranged from 18.5 to ≥40.0 kg/m2. Data were obtained from enrolled women who underwent research ultrasounds at 28 and 36 weeks' gestation. Outcome measures were ultrasound measures of fetal biometry and adiposity.

RESULTS

 Infants born LGA had larger fetal biometry measures, and higher growth trajectories, from 20 weeks' gestation. Fetal adiposity measures were consistently larger among infants born LGA and these differences increased over time. We did not find evidence that the differences in biometry and adiposity measurements varied according to maternal BMI.

CONCLUSION

 Infants born LGA had larger fetal biometry measures at all time points from 20 weeks' gestation, compared with infants born not LGA suggesting any interventions to prevent LGA likely need to commence earlier in pregnancy or prior to conception.

KEY POINTS

· Infants born LGA had larger fetal biometry measures from 20 weeks' gestation.. · Infants born LGA had larger fetal adiposity measures.. · Interventions to prevent LGA need to start earlier in pregnancy or prior to conception..

Routine third-trimester ultrasound assessment for intrauterine growth restriction

Intrauterine growth restriction significantly impacts perinatal outcomes. Undetected IUGR escalates the risk of adverse outcomes. Serial symphysis-fundal height measurement, a recommended strategy, is insufficient in detecting abnormal fetal growth. Routine third-trimester ultrasounds significantly improve detection rates compared with this approach, but direct high-quality evidence supporting enhanced perinatal outcomes from routine scanning is lacking. In assessing fetal growth, abdominal circumference alone performs comparably to estimated fetal weight. Hadlock formulas demonstrate accurate fetal weight estimation across diverse gestational ages and settings. When choosing growth charts, prescriptive standards (encompassing healthy pregnancies) should be prioritized over descriptive ones. Customized fetal standards may enhance antenatal IUGR detection, but conclusive high-quality evidence is elusive. Emerging observational data suggest that longitudinal fetal growth assessment could predict adverse outcomes better. However, direct randomized trial evidence supporting this remains insufficient.

Fetal Growth Velocity according to the Mode of Assisted Conception

INTRODUCTION

Pregnancies conceived through assisted reproductive techniques (ARTs) are on the rise worldwide and have been associated with a higher risk of placental-related disease in the third trimester.

METHODS

A cohort was created of singleton pregnancies after assisted reproduction, admitted at our institution for delivery, between January 2020 and August 2022. Fetal growth velocity from the second trimester to delivery was compared against a gestational-age-matched group of pregnancies spontaneously conceived according to the origin of the selected oocyte (i.e., autologous vs. donated).

RESULTS

125 singleton pregnancies conceived through ART were compared to 315 singleton spontaneous conceptions. Overall, after adjusting for possible confounders, multivariate analysis demonstrated that ART pregnancies had a significantly lower estimated fetal weight (EFW) z-velocity from the second trimester to delivery (adjusted mean difference = -0.002; p = 0.035) and a higher frequency of EFW z-velocity in the lowest decile (adjusted OR = 2.32 [95% CI, 1.15-4.68]). Also, when ART pregnancies were compared according to the type of oocyte, those conceived with donated oocytes showed a significantly lower EFW z-velocity from the second trimester to delivery (adjusted mean difference = -0.008; p = 0.001) and a higher frequency of EFW z-velocity in the lowest decile (adjusted OR = 5.33 [95% CI, 1.34-21.5]).

CONCLUSIONS

Pregnancies achieved through ART exhibit a pattern of lower growth velocity across the third trimester, especially those conceived with donated oocytes. The former represents a sub-group at the highest risk of placental dysfunction that may warrant closer follow-up.

Reduced fetal growth velocity precedes antepartum fetal death

OBJECTIVES

To determine whether decreased fetal growth velocity precedes antepartum fetal death and to evaluate whether fetal growth velocity is a better predictor of antepartum fetal death compared to a single fetal biometric measurement at the last available ultrasound scan prior to diagnosis of demise.

METHODS

This was a retrospective, longitudinal study of 4285 singleton pregnancies in African-American women who underwent at least two fetal ultrasound examinations between 14 and 32 weeks of gestation and delivered a liveborn neonate (controls; n = 4262) or experienced antepartum fetal death (cases; n = 23). Fetal death was defined as death diagnosed at ≥ 20 weeks of gestation and confirmed by ultrasound examination. Exclusion criteria included congenital anomaly, birth at < 20 weeks of gestation, multiple gestation and intrapartum fetal death. The ultrasound examination performed at the time of fetal demise was not included in the analysis. Percentiles for estimated fetal weight (EFW) and individual biometric parameters were determined according to the Hadlock and Perinatology Research Branch/Eunice Kennedy Shriver National Institute of Child Health and Human Development (PRB/NICHD) fetal growth standards. Fetal growth velocity was defined as the slope of the regression line of the measurement percentiles as a function of gestational age based on two or more measurements in each pregnancy.

RESULTS

Cases had significantly lower growth velocities of EFW (P < 0.001) and of fetal head circumference, biparietal diameter, abdominal circumference and femur length (all P < 0.05) compared to controls, according to the PRB/NICHD and Hadlock growth standards. Fetuses with EFW growth velocity < 10^th percentile of the controls had a 9.4-fold and an 11.2-fold increased risk of antepartum death, based on the Hadlock and customized PRB/NICHD standards, respectively. At a 10% false-positive rate, the sensitivity of EFW growth velocity for predicting antepartum fetal death was 56.5%, compared to 26.1% for a single EFW percentile evaluation at the last available ultrasound examination, according to the customized PRB/NICHD standard.

CONCLUSIONS

Given that 74% of antepartum fetal death cases were not diagnosed as small-for-gestational age (EFW < 10^th percentile) at the last ultrasound examination when the fetuses were alive, alternative approaches are needed to improve detection of fetuses at risk of fetal death. Longitudinal sonographic evaluation to determine growth velocity doubles the sensitivity for prediction of antepartum fetal death compared to a single EFW measurement at the last available ultrasound examination, yet the performance is still suboptimal. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.

Customized birth-weight centiles and placenta-related fetal growth restriction

OBJECTIVE

The value of using customized birth-weight centiles to improve the diagnostic accuracy for fetal growth restriction (FGR), in comparison with using population-based charts, remains a matter of debate. One potential explanation for the conflicting data is that most studies used measures of perinatal mortality and morbidity as proxies for placenta-mediated FGR, many of which are not specific and may be confounded by other factors such as prematurity. The aim of this study was to compare the diagnostic accuracy of small-for-gestational age (SGA) at birth, defined according to customized vs population-based charts, for associated abnormal placental pathology.

METHODS

This was a secondary analysis of data from a prospective cohort study on risk factors for placenta-mediated complications and abnormal placental pathology in low-risk nulliparous women. All placentae were sent for detailed histopathological examination by two perinatal pathologists. The primary exposure was SGA, defined as birth weight < 10^th centile for gestational age using either a customized (SGA_cust ) or a population-based (SGA_pop ) birth-weight reference. The outcomes of interest were one of three types of abnormal placental pathology associated with FGR: maternal vascular malperfusion (MVM), chronic villitis and fetal vascular malperfusion (FVM). Adjusted relative risks (aRR) with 95% CIs were estimated using modified Poisson regression analysis, with adjustment for smoking, body mass index and aspirin treatment.

RESULTS

A total of 857 nulliparous women met the study criteria. The proportions of infants identified as SGA based on the customized and population-based charts were 12.6% (108/857) and 11.4% (98/857), respectively. A diagnosis of SGA using either customized or population-based charts was associated with an increased risk of any placental pathology (aRR, 3.04 (95% CI, 2.29-4.04) and 1.60 (95% CI, 1.10-2.31), respectively) and MVM pathology (aRR, 12.33 (95% CI, 6.60-23.03) and 5.29 (95% CI, 2.87-9.76), respectively). SGA_cust , but not SGA_pop , was also associated with an increased risk for chronic villitis (aRR, 1.85 (95% CI, 1.07-3.18)) and FVM pathology (aRR, 2.48 (95% CI, 1.25-4.93)). SGA_cust had a higher detection rate for any placental pathology (30.3% vs 17.1%; P < 0.001), MVM pathology (63.2% vs 39.5%; P = 0.003) and chronic villitis (20.8% vs 8.3%; P = 0.007) than did SGA_pop , for a similar false-positive rate. This was mainly the result of a higher detection rate for abnormal pathology in the white and East-Asian subgroups and a lower false-positive rate for abnormal pathology in the South-Asian subgroup by SGA_cust than by SGA_pop . In addition, pregnancies in the SGA_cust group, but not those in the SGA_pop group, were more likely to be complicated by preterm birth and a low 5-min Apgar score than were the corresponding non-SGA group.

CONCLUSION

These findings suggest that customized birth-weight centiles may be superior to population-based birth-weight centiles in detecting FGR that is due to underlying placental disease. © 2020 International Society of Ultrasound in Obstetrics and Gynecology.

Effect of metformin in addition to an antenatal diet and lifestyle intervention on fetal growth and adiposity: the GRoW randomised trial

BACKGROUND

The infants born to women who are overweight or obese in pregnancy are at an increased risk of being born macrosomic or large for gestational age. Antenatal dietary and lifestyle interventions have been shown to be ineffective at reducing this risk. Our aim was to examine the effects of metformin in addition to a diet and lifestyle intervention on fetal growth and adiposity among women with a BMI above the healthy range.

METHODS

Women who had a body mass index ≥25 kg/m² in early pregnancy, and a singleton gestation, were enrolled in the GRoW trial from three public maternity hospitals in metropolitan Adelaide. Women were invited to have a research ultrasounds at 28 and 36 weeks' gestation at which ultrasound measures of fetal biometry and adiposity were obtained. Fetal biometry z-scores and trajectories were calculated. Measurements and calculations were compared between treatment groups. This secondary analysis was pre-specified.

RESULTS

Ultrasound data from 511 women were included in this analysis. The difference in femur length at 36 weeks' gestation was (0.07 cm, 95% CI 0.01-0.14 cm, p = 0.019) and this was was statistically significant, however the magnitude of effect was small. Differences between treatment groups for all other fetal biometry measures, z-scores, estimated fetal weight, and adiposity measures at 28 and 36 weeks' gestation were similar.

CONCLUSIONS

The addition of metformin to dietary and lifestyle advice in pregnancy for overweight and obese women has no clinically relevant effect on ultrasound measures of fetal biometry or adiposity.

TRIAL REGISTRATION

Australian and New Zealand Clinical Trials Registry ( ACTRN12612001277831 ).

Small-for-gestational-age babies after 37 weeks: impact study of risk-stratification protocol

OBJECTIVE

Although no clear evidence exists, many international guidelines advocate early-term delivery of small-for-gestational-age (SGA) fetuses. The aim of this study was to determine whether a risk-stratification protocol in which low-risk SGA fetuses are managed expectantly beyond 37 weeks affects perinatal and maternal outcomes.

METHODS

This was an impact study examining data collected over a 39-month period (1 January 2013 to 30 April 2016) at a tertiary referral unit. The study included women who were referred to the fetal medicine unit with a singleton non-anomalous fetus diagnosed antenatally as SGA (estimated fetal weight < 10^th centile) from 36 + 0 weeks' gestation. In 2014, a protocol for management of SGA was introduced, which included risk stratification with surveillance and expectant management after 37 weeks for lower-risk babies (protocol group). This was compared with the previous strategy, which recommended delivery at around 37 weeks (pre-protocol group). Primary outcome was neonatal composite adverse outcome.

RESULTS

In the pre-protocol group, there were 138 SGA babies; in the protocol group there were 143. Mean gestational ages at delivery were 37.4 weeks in the pre-protocol group and 38.2 weeks in the protocol group (P = 0.04). The incidence of neonatal composite adverse outcome was lower in the protocol group (9% vs 22%; P < 0.01), as was neonatal unit admission (13% vs 39%; P < 0.01). Induction of labor and Cesarean section rates were lower, and vaginal delivery rate (83% vs 60%; P < 0.01) was higher, in the protocol group. Most of the differences were as a result of delayed delivery of SGA babies that were stratified as low risk.

CONCLUSIONS

The findings of this study suggest that protocol-based management of SGA babies may improve outcome, and that identification of moderate SGA should not in isolation prompt delivery. Larger numbers are required to assess any impact on perinatal mortality. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Fetal growth velocity and body proportion in the assessment of growth

Fetal growth restriction implies failure of a fetus to meet its growth potential and is associated with increased perinatal mortality and morbidity. Therefore, antenatal detection of fetal growth restriction is of major importance in an attempt to deliver improved clinical outcomes. The most commonly used approach towards screening for fetal growth restriction is by means of sonographic fetal weight estimation, to detect fetuses small for gestational age, defined by an estimated fetal weight <10th percentile for gestational age. However, the predictive accuracy of this approach is limited both by suboptimal detection rate (as it may overlook non-small-for-gestational-age growth-restricted fetuses) and by a high false-positive rate (as most small-for-gestational-age fetuses are not growth restricted). Here, we review 2 strategies that may improve the diagnostic accuracy of sonographic fetal biometry for fetal growth restriction. The first strategy involves serial ultrasound evaluations of fetal biometry. The information obtained through these serial assessments can be interpreted using several different approaches including fetal growth velocity, conditional percentiles, projection-based methods, and individualized growth assessment that can be viewed as mathematical techniques to quantify any decrease in estimated fetal weight percentile, a phenomenon that many care providers assess and monitor routinely in a qualitative manner. This strategy appears promising in high-risk pregnancies where it seems to improve the detection of growth-restricted fetuses at increased risk of adverse perinatal outcomes and, at the same time, decrease the risk of falsely diagnosing healthy constitutionally small-for-gestational-age fetuses as growth restricted. Further studies are needed to determine the utility of this strategy in low-risk pregnancies as well as to optimize its performance by determining the optimal timing and interval between exams. The second strategy refers to the use of fetal body proportions to classify fetuses as either symmetric or asymmetric using 1 of several ratios; these include the head circumference to abdominal circumference ratio, transverse cerebellar diameter to abdominal circumference ratio, and femur length to abdominal circumference ratio. Although these ratios are associated with small for gestational age at birth and with adverse perinatal outcomes, their predictive accuracy is too low for clinical practice. Furthermore, these associations become questionable when other, potentially more specific measures such as umbilical artery Doppler are being used. Furthermore, these ratios are of limited use in determining the etiology underlying fetal smallness. It is possible that the use of the 2 gestational-age-independent ratios (transverse cerebellar diameter to abdominal circumference and femur length to abdominal circumference) may have a role in the detection of mild-moderate fetal growth restriction in pregnancies without adequate dating. In addition, despite their limited predictive accuracy, these ratios may become abnormal early in the course of fetal growth restriction and may therefore identify pregnancies that may benefit from closer monitoring of fetal growth.

The systematic error in the estimation of fetal weight and the underestimation of fetal growth restriction

Fetal growth restriction (FGR) is associated with an increased risk of perinatal morbidity and mortality and has lifetime implications for the risk of chronic medical conditions. Antenatal diagnosis of FGR remains poor, with the majority of cases remaining undiagnosed. Although several factors contribute to the underdiagnosis of FGR, the error in ultrasound estimation of fetal weight (EFW) generally is not considered in clinical practice. In this commentary, we suggest that the intrinsic, or systematic, error in ultrasound EFW is a significant factor contributing to the underestimation of fetuses predicted to have FGR and should be incorporated into screening and surveillance recommendations. To illustrate this point, we present an analytic model of published data from the Eunice Kennedy Shriver National Institute of Child Health and Human Development Fetal Growth Studies characterizing and quantifying the impact of the systematic error in ultrasound EFW on the underdiagnosis of FGR. Independent of the centile at which the risk of adverse outcome related to FGR begins, whether the 10th, 5th or 3rd percentile, our analysis suggests the need to modify to the current paradigm for identifying and responding to fetuses estimated to be at risk.

Computing the Z Score and Centiles for Cross-sectional Analysis: A Practical Approach

Although Z scores have been reported in the literature, one of the problems for the nonstatistician is understanding the systematic approach used to compute the predicted mean and standard deviation, components of the Z score equation, which may vary as the independent variable changes over time (eg, gestational age). This review focuses on a step-by-step analysis using linear, quadratic, and fractional polynomials to compute the mean and standard deviation as a function of a continuous independent variable. Once the mean and standard deviation are computed, the Z score and centile can be derived and Z score calculators created that enable investigators to implement the results in the laboratory and/or clinical setting.

Prediction of adverse perinatal outcome of small-for-gestational-age pregnancy using size centiles and conditional growth centiles

OBJECTIVE

To test whether adding conditional growth centiles to size centiles of estimated fetal weight (EFW) improves prediction of adverse perinatal outcome in pregnancies with or at risk of having a small-for-gestational-age (SGA) fetus.

METHODS

This prospective longitudinal study included pregnant women at risk of or diagnosed with an SGA (≤ 5(th) centile) fetus. They underwent serial ultrasound measurements and the final two were included in the analyses for this study. The EFW was categorized into normal (> 5(th) or 10(th) centile) and abnormal (≤ 5(th) or 10(th) centile) for size and conditional growth before entering the variables into log-binomial regression analyses. Adverse outcomes were delivery < 37 weeks, operative delivery due to fetal distress, 5-min Apgar score < 7, newborn hypoglycemia (glucose < 2.0 mmol/L), admission to the neonatal intensive care unit and perinatal mortality. A combined outcome variable ('any adverse outcome') included one or more adverse outcomes.

RESULTS

Complete biometric data were obtained for 211 women. Conditional growth and size centiles contributed independently to the prediction of adverse outcome. Combining conditional growth and size centiles significantly improved the prediction of outcomes compared with size centiles alone (e.g. for 5(th) centile cut-off for any adverse outcome, P = 0.023, log-likelihood test). Using a 5(th) centile threshold, for any adverse outcome, the specificity of 78% (95% CI, 70-84%) using size centile as a predictor was improved to 94% (95% CI, 89-97%) when conditional growth centile was added to the model, whereas the sensitivity was not significantly changed (60% (95% CI, 49-69%) vs 39% (95% CI, 30-50%)).

CONCLUSIONS

Size centiles and conditional growth centiles contribute independently to the prediction of adverse perinatal outcome, and their combination further improves the prediction model. The results support an increased use of conditional growth centiles in the monitoring of fetuses at risk. Copyright © 2015 ISUOG. Published by John Wiley & Sons Ltd.

Small Size at Birth or Abnormal Intrauterine Growth Trajectory: Which Matters More for Child Growth?

Small size at birth is linked with lifelong adverse health implications. However, small size is only a proxy for the pathological process of interest, intrauterine growth restriction. We examined the extent to which information on intrauterine growth patterns improved prediction of childhood anthropometry, above and beyond birth weight alone. We obtained fetal weights estimated via serial ultrasound for 478 children in the Scandinavian Successive Small-for-Gestational-Age Births Study (1986-1988). Size at birth was classified using birth weight-for-gestational-age z scores and conditional fetal growth z scores (reflecting growth between 25 weeks' gestation and birth) using internal references. Conditional z scores were also expressed as residuals of birth weight z scores. Growth measures were linked with age-5-years anthropometric characteristics using linear regression. In univariable analyses, conditional fetal growth z scores were positively associated with z scores for child height, body mass index, total skinfold thickness, and head circumference (β = 0.24 (95% confidence interval (CI): 0.18, 0.31), β = 0.16 (95% CI: 0.09, 0.23), β = 0.08 (95% CI: 0.01, 0.16), and β = 0.37 (95% CI: 0.22, 0.52), respectively). However, conditional z scores were highly correlated with birth weight z scores (r = 0.9), and residuals explained minimal additional variation in anthropometric factors (null coefficients; adjusted R(2) increases < 0.01). Information on the intrauterine trajectory through which birth weight was attained provided little additional insight into child growth beyond that obtained from absolute size at birth.

Models of hypoxia and ischemia-induced seizures

Despite greater understanding and improved management, seizures continue to be a major problem in childhood. Neonatal seizures are often refractory to conventional antiepileptic drugs, and can result in later life epilepsy and cognitive deficits, conditions for which there are no specific treatments. Hypoxic and/or ischemic encephalopathy (HIE) is the most common cause for neonatal seizures, and accounts for more than two-thirds of neonatal seizure cases. A better understanding of the cellular and molecular mechanisms is essential for identifying new therapeutic strategies that control the neonatal seizures and its cognitive consequences. This heavily relies on animal models that play a critical role in discovering novel mechanisms underlying both epileptogenesis and associated cognitive impairments. To date, a number of animal models have provided a tremendous amount of information regarding the pathophysiology of HIE-induced neonatal seizures. This review provides an overview on the most important features of the main animal models of HIE-induced seizures. In particular, we focus on the methodology of seizure induction and the characterizations of post-HIE injury consequences. These aspects of HIE-induced seizure models are discussed in the light of the suitability of these models in studying human HIE-induced seizures.

Does low-molecular-weight heparin influence fetal growth or uterine and umbilical arterial Doppler in women with a history of early-onset uteroplacental insufficiency and an inheritable thrombophilia? Secondary randomised controlled trial results

OBJECTIVE

Does low-molecular-weight heparin (LMWH) added to low-dose aspirin influence fetal growth and flow velocity in uterine and umbilical arteries in women with an inheritable thrombophilia and previous early-onset uteroplacental insufficiency?

DESIGN

Secondary outcomes of the FRUIT-RCT.

SETTING

Multicentre, international.

POPULATION

The FRUIT-RCT included 139 women with inheritable thrombophilia before 12 weeks of gestation. Inclusion criteria were previous delivery before 34 weeks of gestation with a hypertensive disorder of pregnancy and/or small-for-gestational-age infant and an inheritable thrombophilia.

METHODS

After randomisation to either daily LMWH with aspirin, or aspirin only, ultrasound measurements were performed at 22-24, 28-30 and 34-36 weeks of gestation. Development during gestation of growth, birthweight and flow velocity of the umbilical artery was examined using the linear mixed model. Uterine artery flow velocity at a single time-point (22-24 weeks) was examined using a chi-square test.

MAIN OUTCOME MEASURES

Fetal growth over time including birthweight, using Scandinavian, Dutch and customised growth curves; and flow velocity within the uterine and umbilical arteries.

RESULTS

No difference of fetal growth over time could be demonstrated between the study arms, regardless of which reference criteria were used. The flow velocity within the uterine artery and umbilical artery did not differ between study arms.

CONCLUSION

The addition of LMWH to aspirin did not influence fetal growth or umbilical artery flow velocity over time; nor did it influence uterine artery flow velocity.

TWEETABLE ABSTRACT

LMWH does not influence fetal growth or uterine or umbilical flow velocities.

Foetal growth velocities in twin pregnancies

A retrospective longitudinal study was performed to quantify foetal growth velocities in twin pregnancies and to determine the effect of variables specific to twin pregnancies on growth velocity. Foetal growth velocity standard deviation (Z) scores were calculated from serial ultrasound data using published singleton reference data for 131 consecutive sets of twins from 30 to 37 weeks' gestation. Compared with low-risk pregnancies, the twin foetal abdominal area growth velocity Z scores were significantly reduced from 30 to 37 weeks and biparietal diameter growth velocity Z scores were also significantly lower, from 30 to 33 weeks. Amongst the twin pairs there were no significant differences in Z scores with respect to chorionicity, foetal sex, birth order to whether delivery was premature or term. This retrospective study has demonstrated that twin foetal growth velocity is reduced when compared to singletons from at least as early as 30 weeks' gestation. Twin specific variables such as chorionicity, sex, birth order and subsequent premature birth do not need to be accounted for in the interpretation of growth velocities in twins. The clinical importance of determining foetal growth velocity in twin pregnancies awaits further prospective study.

Self-administered symphysis-fundus measurements analyzed with a novel statistical method for detection of intrauterine growth restriction: a clinical evaluation

OBJECTIVE

To assess the ability of self-administered symphysis-fundus measurements used with the Shiryaev-Roberts statistical method (SR method) to identify growth-restricted (IUGR) fetuses and compare it with the traditional SF method (symphysis-fundus measurements used with a population-based reference curve).

DESIGN

Longitudinal study.

SETTING

Pregnant women attending primary antenatal care centres.

POPULATION

From a population of 1 888 women with singleton ultrasound-dated pregnancies, we analyzed data from 1 122 women.

METHODS

Weekly self-administered SF measurements from gestational week 25 until delivery were analyzed according to the SR method. Neonatal morbidity and small for gestational age (SGA) were used as proxies for IUGR. Small for gestational age was defined as a birthweight less than two standard deviations (SD) and <10th percentile. We assessed the sensitivity of the SR and the SF methods to detect neonatal morbidity and SGA.

MAIN OUTCOME MEASURES

Birth-related mortality, respiratory distress, hypoglycemia, Apgar score ≤6 at five minutes, pH ≤7.00 in the umbilical artery, neonatal care, preterm delivery, operative delivery for fetal distress and SGA. Results. For the SR method, the sensitivity for neonatal morbidity was between 6.0 and 36.4%, for SGA <2SD 36.8%, and for SGA <10th percentile 20.9%. The SF method had a sensitivity between 6.0 and 13.8% for neonatal morbidity, 52.3% for SGA <2SD and 28.6% for SGA <10th percentile.

CONCLUSIONS

The SR and the SF methods had low sensitivities for neonatal morbidity.

Defining normal and abnormal fetal growth: promises and challenges

Normal fetal growth is a critical component of a healthy pregnancy and influences the long-term health of the offspring. However, defining normal and abnormal fetal growth has been a long-standing challenge in clinical practice and research. We review various references and standards that are used widely to evaluate fetal growth and discuss common pitfalls of current definitions of abnormal fetal growth. Pros and cons of different approaches to customize fetal growth standards are described. We further discuss recent advances toward an integrated definition for fetal growth restriction. Such a definition may incorporate fetal size with the status of placental health that is measured by maternal and fetal Doppler velocimetry and biomarkers, biophysical findings, and genetics. Although the concept of an integrated definition appears promising, further development and testing are required. An improved definition of abnormal fetal growth should benefit both research and clinical practice.

Fetal size and growth velocity in the prediction of the large for gestational age (LGA) infant in a glucose impaired population

OBJECTIVES

To evaluate the performances of estimated fetal weight (EFW) and fetal growth velocity (FGV) in the prediction of birth weight>95th centile amongst women with impaired glucose tolerance (IGT); the prediction of neonatal hypoglycaemia was a secondary endpoint.

STUDY DESIGN

Two hundred and forty-two consecutive women (61 type 1 diabetes mellitus, 14 type 2 diabetes mellitus, 49 gestational diabetics and 118 with impaired glucose tolerance) receiving routine care at the combined diabetes/antenatal clinic, Jessop Hospital for Women, Sheffield. EFW was routinely calculated at approximately two-week intervals in the third trimester with the last EFW prior to delivery used in the analysis. FGV was calculated from two estimates of fetal weight between 21 and 35 days apart. EFW and FGV were both expressed as standard deviation (Z) scores.

RESULTS

The mean gestational age at delivery was 37 weeks (range 26-40 weeks). Sixty-five (27%) infants were of birth weight>95th centile. Mean EFW Z scores were 2.7 and 0.99 for >95th and <95th centile, respectively (p<0.001). Receiver operator characteristics (ROC) curve analysis gave area under the curve 0.8; using a cut-off Z score of 1.7 (=95.5 centile), EFW has sensitivity 80% and specificity 72% in predicting an LGA neonate (likelihood ratios 2.8 and 0.27 for positive and negative test). Mean FGV Z scores were 0.85 and 0.4 for >95th and <95th centile, respectively (p>0.05); ROC curve analysis indicated no discriminatory capacity. Estimates of fetal size and growth performed poorly in the prediction of neonatal hypoglycaemia.

CONCLUSION

In routine clinical practice, EFW has limited utility in the prediction of the LGA infant. FGV does not identify the LGA infant. EFW and FGV do not predict neonatal hypoglycaemia.

Maternal body mass index in the first trimester and risk of cesarean delivery in nulliparous women in spontaneous labor

OBJECTIVE

To evaluate the effect of maternal body mass index (BMI) on the incidence of cesarean delivery.

STUDY DESIGN

Prospective observational cohort study of 4341 consecutive nulliparous women with a single cephalic presentation, and spontaneous onset of labor between 37 and 42 weeks gestation at High Wycombe General Hospital, London, between January 1, 1995, and December 31, 2000.

RESULTS

The incidence of cesarean delivery rose significantly with an increase in BMI. Women in labor with a BMI > 35 had a 3.8 times greater chance of a cesarean delivery than women with a BMI < 25 (after adjustment for variables such as maternal height and age, gestational age, fetal birthweight, and use of oxytocin and epidural analgesia during labor). This was true for cesarean deliveries performed for suspected fetal distress as well as for failure to progress.

CONCLUSION

A high BMI significantly increased the risk of cesarean delivery, but the reasons are not certain.

Le contrôle de qualité en échographie prénatale : intérêt de la biométrie

Because of an increasing demand for limited health care resources as well as an increasing impact of legal aspects in ultrasound practice, it has become necessary to ensure that screening procedures are cost-effective and clinically effective and to develop systems that could help sonographists in certifying their practice. Based on the literature, various approaches for quality control are reviewed. Special emphasis is put on the use of fetal biometry and statistical tools to develop quality control systems based on both qualitative and quantitative approach. Besides their potentials for audit and quality control, such tools could also be useful during the process of training.

The impact of choice of reference charts and equations on the assessment of fetal biometry

OBJECTIVES

The assessment of fetal biometry is usually based on the comparison of measured values with predicted values derived from reference charts or equations in a normal population. This study was undertaken to assess the impact of the choice of reference charts and to develop a Z-score-based tool that could help sonographers to choose the reference charts that best fit their practice.

METHODS

Fetal biparietal diameter, head circumference, abdominal circumference and femur diaphysis length measurements were made at 20-24 and 30-34 weeks' gestation by four experienced sonographers. All measurements were transformed into Z-scores calculated according to three prediction equations (Snijders and Nicolaides, 1994; Chitty et al., 1994 and Kurmanavicius et al., 1999). Distributions of Z-scores were compared to the expected standard normal distribution based on mean, SD and Kolmogorov-Smirnov test. Simulations were made to assess sensitivity (Se), specificity (Sp) and Youden's index (Se + Sp - 1) of each reference equation, reflecting their ability to identify fetuses with abnormal biometry in our population. The reference that best fitted our practice was determined based on these results.

RESULTS

The Z-scores of all biometric parameters were significantly different (P < 0.001) when using any of the three reference equations, and none of the Z-score distributions could be considered similar to the standard normal distribution. The number of measurements that would be considered as abnormal according to these references ranged from 2.6% to 23.6%. Se and Sp ranged from 39.59% to 67.12% and 90.14% to 99.69%, respectively.

CONCLUSION

Assessment of fetal biometry is largely dependent on the choice of reference charts. We suggest that the choice of reference charts for fetal biometry could be controlled using Z-scores in each institution and that this could be the first step towards any quality assessment policy. The method we describe for the choice of the most appropriate fetal biometry reference chart might be used for all size charts.

Current concepts in intrauterine growth restriction

Regulation of fetal growth is multifactorial and complex. Diverse factors, including intrinsic fetal conditions as well as maternal and environmental factors, can lead to intrauterine growth restriction (IUGR). The interaction of these factors governs the partitioning of nutrients and rate of fetal cellular proliferation and maturation. Although IUGR is probably a physiologic adaptive response to various stimuli, it is associated with distinct short- and long-term morbidities. Immediate morbidities include those associated with prematurity and inadequate nutrient reserve, while childhood morbidities relate to impaired maturation and disrupted organ development. Potential long-term effects of IUGR are debated and explained by the fetal programming hypothesis. In formulating a comprehensive approach to the management and follow-up of the growth-restricted fetus and infant, physicians should take into consideration the etiology, timing, and severity of IUGR. In addition, they should be cognizant of the immediate perinatal response of the growth-restricted infant as well as the childhood and long-term associated morbidities. A multi disciplinary approach is imperative, including early recognition and obstetrical management of IUGR, assessment of the growth-restricted newborn in the delivery room, possible monitoring in the neonatal intensive care unit, and appropriate pediatric follow-up. Future research is necessary to establish effective preventive, diagnostic, and therapeutic strategies for IUGR, perhaps affecting the health of future generations.

Will there ever be an end to the Caesarean section rate debate?

Caesarean section rates continue to rise. To date, no serious attempt has been made to address this issue. There are no scientific grounds for identifying an 'appropriate' level for Caesarean section rates. A 'Term Cephalic Trial' may provide such information, but poses major logistic and ethical challenges. The authors propose that a combination of known and newly developed predictors of emergency operative delivery may allow an antenatal risk assessment that could make intervention trials both ethically sound and logistically feasible.

Relationship between customised birthweight centiles and neonatal anthropometric features of growth restriction

OBJECTIVE

To determine the relationship between customised birthweight centiles (adjusted for maternal and fetal physiological variables) and neonatal anthropometric features of intrauterine growth restriction (IUGR).

DESIGN

Observational study.

POPULATION

Two-hundred and seventy women with low risk pregnancies participating in a cohort study of serial ultrasound biometry.

METHODS

Customised birthweight centiles were calculated following adjustment for maternal weight, height and ethnic origin, gestational age at delivery, birth order, and sex of the infant. Three separate neonatal anthropometric measures were used to define IUGR: subscapular or triceps skinfold thickness <10th centile; ponderal index <25th centile; and mid-arm circumference to occipito-frontal circumference ratio (MAC/OFC) <- 1 standard deviation (SD). Relationship of the centiles to these outcomes was evaluated using likelihood ratios (LR) and kappa statistic. These approaches allowed us to examine the strength of the association: an LR of 5-10 would be expected to generate moderate changes in the pre-test probability of IUGR, whereas a kappa value of 0.2-0.4 would reflect fair agreement between customised birthweight centiles and neonatal anthropometric measures.

RESULTS

Customised birthweight centile of 10 or less had the following LR values for the various anthropometric criteria for IUGR: 5.1 (95% CI 3-8.5) for low skinfold thickness; 4.3 (95% CI 2.5-7.1) for low ponderal index; and 3.9 (95% CI 2-6.6) for low MAC/OFC ratio. The kappa values were: 0.4 (95% CI 0.26-0.51) for low skinfold thickness; 0.33 (95% CI 0.21-0.46) for low ponderal index; and 0.13 (95% CI 0-0.26) for low MAC/OFC ratio.

CONCLUSION

In a low risk population, customised birthweight centiles can only be moderately useful in the identification of neonates with low skinfold thickness and low ponderal index.

Abdominal circumference: a single measurement versus growth rate in the prediction of intrapartum Cesarean section for fetal distress

OBJECTIVE

The fetal abdominal circumference is the most sensitive ultrasound biometric measurement for predicting intrauterine growth restriction, which is associated with an increased risk of intrapartum fetal distress. We sought to evaluate and compare whether a third-trimester ultrasound measurement of abdominal circumference made within 1 week prior to delivery better predicts operative delivery for fetal distress when compared with the growth velocity of the abdominal circumference in the third trimester.

METHODS

Retrospective analysis was carried out of prospectively collected ultrasound data on 117 patients with singleton gestations who had had at least two ultrasound assessments performed less than 6 weeks apart in the third trimester, with the last ultrasound performed within 1 week prior to delivery. The abdominal circumference value of the last ultrasound prior to delivery was placed into one of three categories: < or = 5% centile, > 5 to < or = 10% centile and > 10% centile for gestational age. The growth velocity of the abdominal circumference per week was placed into one of three categories: < or = 5 mm/week, 6-10 mm/week and > or = 11 mm/week. The chi-squared test was used to compare differences between the incidence of fetal distress between the groups.

RESULTS

The incidences of Cesarean section for fetal distress in relation to a single measurement of the abdominal circumference were: < or = 5% centile, 8/23 (35%); > 5 to < or = 10% centile, 3/12 (25%); > 10% centile, 8/81 (10%) ( P < 0.05). The incidences of Cesarean section for fetal distress with the three abdominal circumference growth velocities were: < or = 5 mm/week, 9/55 (16%); 6-10 mm/week, 4/11 (36%); > or = 11 mm/week, 8/51 (16%) ( P = 0.9401).

CONCLUSION

A single measure of the fetal abdominal circumference made within 1 week prior to delivery is superior to an assessment of growth rate of the fetal abdomen in the third trimester in discriminating patients who require Cesarean section for fetal distress.

The fetal outcome in pregnancies with isolated reduced amniotic fluid volume in the third trimester

Our aim was to assess the outcome of pregnancies where oligohydramnios, defined by a published gestational reference range for amniotic fluid index, was the only abnormal finding at third trimester scan, and all other ultrasound parameters including biometry were within normal limits at initial scan. A retrospective case-control study was performed at The Liverpool Maternity Hospital. 103 pregnancies with reduced amniotic fluid index in the third trimester and apparently normal fetal growth profile ultrasonographically were identified from ultrasound reports throughout 1993. Pregnancies in the third trimester with normal amniotic fluid index on index scan were also identified from these reports and 103 were matched for parity, gestational age at delivery, mode of onset of labour, presentation at labour and medical conditions. Exclusion criteria were ruptured membranes, fetal abnormalities, estimated fetal weight below the fifth centile at index scan and multiple pregnancies. The outcome criteria were birthweight, Apgar scores at delivery, induction and emergency delivery for fetal reasons and admission to Neonatal Intensive Care Unit. Statistical analysis was performed by Fisher's exact test and Gart's odds ratio. Compared with controls, pregnancies in the reduced liquor group had a higher number of babies below the 5th centile (odds ratio 5.2, 95% confidence interval 1.6 to 22), a higher risk of induction for fetal reasons (odds ratio 34.4, 95% confidence interval 5.35 to 1425.5) and admission to Neonatal Intensive Care Unit (odds ratio 9.77, 95% confidence interval 1.3 to 432). Any observed difference in the need for emergency delivery due to fetal reasons was not clinically significant (odds ratio 2.16, 95% confidence interval 0.77 to 6.6) The definition used for oligohydramnios used in this study appears to identify a group of babies with a fourfold risk of low birthweight and a high risk of admission to the Neonatal Intensive Care Unit and induction of labour for fetal reasons. This would suggest that pregnancies with isolated oligohydramnios require some form of fetal monitoring and further prospective studies are required to determine the most appropriate method.

Fetal ultrasound biometry: 1. Head reference values

OBJECTIVE

To create reliable reference ranges and calculate Z scores for fetal head ultrasound biometry using a large sample size which is evenly distributed from 12 to 42 weeks of pregnancy.

DESIGN

A prospective, cross-sectional study.

SETTING

Obstetric clinics (outpatient and delivery units) at the University Hospital of Zurich.

SAMPLE

The study data were obtained from 6557 pregnant women.

METHODS

Only the first ultrasound examination between 12 and 42 weeks of each fetus with exactly established gestational age was used for analysis. No exclusions were made on the grounds of small-for-date birthweight, prematurity or other events several weeks after the examination. Separate regression models were fitted to estimate the mean and standard deviation at each gestational age for each parameter.

RESULTS

A total of 6217 fetal head biparietal diameters and 5510 occipito-frontal diameters were measured. Both head circumference and cephalic index were derived in 5462 cases where both biparietal diameter and occipito-frontal diameter could be measured on the same fetus. The centile charts, tables and regression formulae for biparietal and occipito-frontal diameters, head circumference and cephalic index are presented. An application to calculate Z scores was developed using Excel (Microsoft Corporation, USA) and macros are presented in detail in the Figure 8 footnote. The comparison of our charts with those of the two most recent studies revealed almost no differences in biparietal diameter centiles. In one publication, occipito-frontal diameter charts, and in another, head circumference charts were different from the current study.

CONCLUSIONS

We have presented centile charts, tables and regression formulae for fetal head ultrasound biometry derived from a large and minimally selected sample size in a carefully designed cross-sectional study. Complete tables and regression formulae to calculate reference ranges and Z scores are presented for use in computer-aided evaluation of fetal ultrasound biometry.

Fetal growth velocity in the prediction of intrauterine growth retardation in a low risk population

OBJECTIVE

To determine whether fetal growth velocity derived from two antenatal ultrasound measurements in the third trimester, 28 days apart, can identify infants born with anthropometric features of intrauterine growth retardation.

DESIGN

Prospective observational study.

SETTING

Department of obstetric ultrasound, Ninewells Hospital, Dundee.

SUBJECTS

Two hundred and seventy four low risk women participating in a longitudinal study of serial fortnightly ultrasound in pregnancy.

METHODS

Growth velocities of the fetal abdominal area and bi-parietal diameter were calculated from the third from last and last measurements prior to delivery. Receiver Operator Characteristics curves were employed to determine an optimal cutoff point for velocity to predict intrauterine malnourishment.

MAIN OUTCOME MEASURES

Likelihood ratios for fetal abdominal area and bi-parietal diameter growth velocity in the prediction of growth retarded infants with skinfold thickness < 10th centile; ponderal index < 25th centile, or mid-arm circumference to occipito-frontal circumference ratio (MAC:OFC ratio) of less than -1 SD. A likelihood ratio of > 10 generates significant changes in the pre-test probability of growth retardation, whereas a likelihood ratio of 5 to 10 generates only moderate changes.

RESULTS

Fetal abdominal area velocity predicted growth retardation with likelihood ratio 10.4 (95% CI 3.9 to 26) for skinfold thickness; likelihood ratio 9.5 (95% CI 4.6 to 19) for ponderal index; a likelihood ratio 4.7 (2.3 to 8.4) for MAC:OFC. Bi-parietal diameter velocity predicted growth retardation with likelihood ratio 6.5 (95% CI 1.9 to 20) for skinfold thickness but did not predict low ponderal index or MAC:OFC ratio.

CONCLUSIONS

Fetal abdominal area velocity is useful in identifying infants with reduced skinfold thickness or low ponderal index. Prospective evaluation of serial ultrasound and velocity calculation in a selected population at increased risk of growth failure and a clearer understanding of the relative significance of the different neonatal anthropometric measures of impaired growth achievement is necessary before the estimation of growth velocity can be recommended in clinical practice.