The transverse cerebellar diameter in estimating gestational age in the large for gestational age fetus

The transverse cerebellar diameter was measured in 62 nondiabetic and 30 diabetic women with large for gestational age fetuses. Using reference curves from 675 women with normal gestations between 14-42 weeks, head circumference and abdominal circumference overestimated gestational age significantly in both study groups, whereas the transverse cerebellar diameter did not.     

Estimation of gestational age with ultrasonographic measurement of the fetus in each trimester

The method of estimating gestational age (GA) was studied in each trimester. CRL, BPD and FFL were selected as the parameters of ultrasonic B-mode measurement, and each standard curve was recorded. The less erroneous range on each parameter was decided. The range of CRL was from 20 to 80mm, that of BPD from 20 to 70 mm and that of FFL from 20 to 55mm. Within these ranges, GA estimated by CRL showed 2.9 days difference on average compared to the GA determined by LMP, compared with BPD 4.6 days and with FFL 4.9 days. CRL was the most accurate, but that with BPD or FFL could be useful in the 2nd trimester. Since the difference in the growth of each fetus would become apparent in late stage, the ranges of GA for each measured value of BPD or FFL were determined in the 3rd trimester by the mean +/- 3/2 SD for GA determined by CRL. Since 67 to 100% of the studied cases were included in the ranges of GA, the estimation will be useful in the 3rd trimester. FFL is more useful than BPD in the 3rd trimester, and it is also utilized in cases where BPD measurement is not possible due to fetal head descent.     

Ultrasound estimation of fetal weight in small for gestational age pregnancies

Objective.?Approximately half of small for gestational age (SGA) cases are due to maternal or fetal pathology, and may result in significant neonatal morbidity and mortality. The estimated fetal weight (EFW) measurement is the cornerstone of ultrasonographic findings when diagnosing and managing SGA pregnancies. Our objective was to determine the ultrasound accuracy of EFW in SGA pregnancies.

Methods.?A retrospective chart review was performed of all pregnancies complicated by SGA from a single institution (Stanford University) over a 2-year-period (2004–2006). SGA was defined as EFW?≤?10%. 98 neonates whose last ultrasound for EFW occurred within 7 days of delivery were included in the study. The absolute differences between the EFW and birthweight (BW) were analyzed, and the absolute percent errors were calculated as (EFW???BW)/BW?× 100. The mean absolute differences and mean absolute percent errors were analyzed across all gestational ages (GA) and EFWs using one-way analysis of variance.

Results.?The mean absolute percent error for the entire cohort was 8.7% (±6.3%). There was no statistically significant difference in the mean absolute percent error across all GAs (<32 weeks, 32–36 weeks, >36 weeks), and EFWs (<1500?g, 1500–2000?g, >2000?g).

Conclusion.?Ultrasound measurement of EFW in SGA pregnancies is consistent across all GAs and EFW measurements.     

A comparison of sonographic estimation of fetal weight and obstetrically determined gestational age in the prediction of neonatal outcome for the very low-birth weight fetus

A comparison of sonographic estimation of fetal weight and obstetrically determined gestational age in the prediction of neonatal outcome for the very low-birth weight fetus was conducted in a study population of 122 fetuses. With stepwise logistic regression, obstetric gestational age was found to be the best predictor of neonatal death, while sonographic estimated fetal weight did not add significantly to this prediction. However, both variables were important in the prediction of adverse neonatal outcome (neonatal death together with major neonatal complications of prematurity.     

Ultrasonographic weight estimation in large for gestational age fetuses: A comparison of 17 sonographic formulas and four models algorithms

Objective.?To evaluate the accuracy of different formulas and role of fetal parameters (cephalic, abdominal, femur) used for estimation fetal weight (EFW) in large for gestational age (LGA) fetus in diabetic and non-diabetic mothers.

Methods.?Seventeen formulas were assessed individually and clustered in four algorithms (X, Y, Z, W) on the basis of fetal biometric parameters using the mean absolute % error, standard deviation (SD), prediction within?±5%,?±10%,?±15% of error and introducing new variable hypotenuse test (HPT) that can sum up precision and accuracy of formulas employed. For predicting fetal macrosomia (BW?≥?4200?g) a receiver-operating characteristic curve was constructed.

Results.?Warsof2 formula showed the lowest mean % error, SD and HPT (p?<?0.01) with overall prediction ±5,?±10%,?±15% of birth weight in 68, 94 and 98%. The formulas that were only based on abdominal measurement (Warsof2, Hadlock1, Campbell) showed the best ability to identify fetal macrosomia. The X algorithm confirming primary role of abdominal circumference for EFW in diabetic mothers.

Conclusions.?Accuracy of EFW in LGA fetuses is attributable to the biometric parameters used. Our findings show that the best formulas for EFW are those which only consider the abdominal measurements, especially in diabetic mothers. The new variable that we propose (HPT) confirms this result.     

Accuracy of ultrasonic fetal weight estimation and detection of small for gestational age fetuses

One hundred and eight-six pregnant women were studied with ultrasound for clinical suspicion of poor fetal growth. Fetal weight was estimated using biparietal diameter and mean abdominal diameter with a special nomogram. The fetal femur length (FL) to abdominal circumference (AC) ratio was also calculated. The mean interval between the last ultrasound examination and delivery was 9 days (range, 0 to 14 days). Eighty-three women had their last ultrasonic examination 0 to 4 days (mean, 2 days) before delivery. In this group the arithmetic mean of weight estimation errors was -1 gm (SD, 159 gm). The signed mean percent error was +0.6% (SD, 6.6%). Neither systematic nor random errors were found between different growth percentile groups. When small for gestational age (SGA) was defined as birthweight below 2.5 percentile, the sensitivity, specificity, and positive predictive value of the weight estimations were 82%, 92%, and 84%, respectively, in 186 cases. Significant differences were found in FL to AC ratios between growth pattern groups but fetal weight estimation was found to be superior in the detection of SGA fetuses.     

Excessive gestational weight gain predicts large for gestational age neonates independent of maternal body mass index

Objective: To determine the effects of maternal pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) on large-for-gestational-age (LGA) birth weight (≥90th % ile). Methods: We examined 4321 mother-infant pairs from the Ottawa and Kingston (OaK) birth cohort. Multivariate logistic regression (controlling for gestational and maternal age, pre-pregnancy weight, parity, smoking) were performed and odds ratios (ORs) calculated. Results: Prior to pregnancy, a total of 23.7% of women were overweight and 16.2% obese. Only 29.3% of women met GWG targets recommended by the Institute of Medicine (IOM), whereas 57.7% exceeded the guidelines. Adjusting for smoking, parity, age, maternal height, and achieving the IOM’s recommended GWG, overweight (OR 1.99; 95%CI 1.17–3.37) or obese (OR 2.64; 95% CI 1.59–4.39) pre-pregnancy was associated with a higher rate of LGA compared to women with normal BMI. In the same model, exceeding GWG guidelines was associated with higher rates of LGA (OR 2.86; 95% CI 2.09–3.92), as was parity (OR 1.49; 95% CI 1.22–1.82). Smoking (OR 0.53; 95%CI 0.35–0.79) was associated with decreased rates of LGA. The adjusted association with LGA was also estimated for women who exceeded the GWG guidelines and were overweight (OR 3.59; 95% CI 2.60–4.95) or obese (OR 6.71; 95% CI 4.83–9.31). Conclusion: Pregravid overweight or obesity and gaining in excess of the IOM 2009 GWG guidelines strongly increase a woman’s chance of having a larger baby. Lifestyle interventions that aim to optimize GWG by incorporating healthy eating and exercise strategies during pregnancy should be investigated to determine their effects on LGA neonates and down-stream child obesity.     

The use of a neural network for the ultrasonographic estimation of fetal weight in the macrosomic fetus.

The error associated with regression analysis methods for the ultrasonographic estimation of fetal weight in the suspected macrosomic fetus, approximately 10%, is clinically unacceptable. This study was undertaken to evaluate the applicability of an emerging technique, biologically simulated intelligence, to this problem. One hundred patients with suspected macrosomic fetuses underwent ultrasonographic measurements of biparietal diameter, head and abdominal circumference, femur length, abdominal subcutaneous tissue, and amniotic fluid index. The biologically simulated intelligence model included gestational age, fundal height, age, gravidity, and height. The model was then compared with results obtained from previously published formulas relying on the abdominal circumference and femur length. The biologically simulated intelligence yielded an average error of 4.7% from actual birth weight, statistically better (p = 0.001) than the results obtained from regression models.     

Investigation and management of the small for gestational age fetus

The desire to identify the small for gestational age fetus is due to its association with stillbirth and poorer neonatal outcomes. The difficulty lies in determining which of these babies are just constitutionally small and healthy and which are growth restricted fetuses that are at significant risk of poor outcomes. Fetal growth restriction is often mediated through placental disease and shares a similar aetiological pathway to preeclampsia. Placental malperfusion results in impaired nutrient and oxygen delivery to the fetus. Appropriate risk assessment in early pregnancy and monitoring with symphysis fundal height measurement or ultrasound scans is a crucial part of the screening pathway. There is no effective treatment for growth restriction, so management is based on close monitoring and early delivery. Fetal growth restriction has better defined monitoring and delivery timing guidelines whereas it is more unclear and variable for fetuses considered only to be small for gestational age.     

Ultrasound estimation of gestational age

Many ultrasonologists feel that if they are unable to obtain a BPD measurement at the time of an ultrasound examination that they have somehow failed to do an adequate job. However, from the information outlined in this chapter, it can be seen that the biparietal diameter is only one measurement that can be taken of the fetus in order to estimate gestational age. Furthermore, since the recognition of variability in fetal head shape, absolute reliance on measurement of the fetal biparietal diameter for estimation of gestational age has become much less common, especially after 20 weeks of gestation. The move toward measurement of several parts of the fetal anatomy has been called fetal biometry. The purpose of this approach is to evaluate body proportion and symmetry of growth of different organ systems, in the hope of elucidating subtle patterns which might be recognized as abnormal in very early stages when some form of prenatal management might improve reproductive outcome. Simultaneously, with the implementation of this approach to estimating age, a desire to inject an element of "quality control" into the obstetric ultrasound examination has come about. It has been found that measurement of more than one fetal parameter, in a sense, prevents overreliance on any single measurement, which, by itself, might mislead the clinician. While an error of clinically significant magnitude can be made in any measurement, it is unlikely that an error of the same magnitude, in "the same direction" of over or underestimation of the actual, would occur. Thus, there is an element of protection of the patient built into this approach which makes it appealing intuitively. However, it is uncertain that measurement of BPD, head circumference, abdominal circumference, and femur length will, in all cases, give a better estimate of gestational age than will measurement of the BPD alone. Recent data from Hadlock et al. showed that in 177 normal pregnancies, there was significant improvement in the ultrasound estimation of estimated date of delivery when two or more parameters were used to make that estimate rather than just BPD alone. Prior to 36 weeks, the optimal combination of parameters included the biparietal diameter, the abdominal circumference, and the femur length. However, after 36 weeks, the head circumference, abdominal circumference, and femur length gave the best estimate, with significant reduction in the mean errors, standard deviations, and size of maximum errors. Thus, it appears that the estimate using MFGP is both more accurate and precise than a single measurement.(ABSTRACT TRUNCATED AT 400 WORDS)     

Birth weight for gestational age centiles for Italian neonates

Objective: To provide centiles for birth weight (BW) according to gestational age (GA) and sex for infants born in Italy.

Methods: We used records of the whole neonatal population of Tuscany, a region in Italy, from July 1991 to June 2002 as resulting from the database of the cystic fibrosis neonatal screening program (n?=?290?129). We excluded as unlikely for GA those BW that were more than two interquartile ranges above the 75th centile or below the 25th centile for each GA and gender group.

Results: We present the 3rd, 10th, 25th, 50th, 75th, 90th and 97th centiles of BW for GA from the 24th to 43rd week of gestation for male and female Italian neonates, as both tables and smoothed curves.

Conclusions: The large size of the examined population allows us to provide up-to-date, reliable BW for GA centiles for Italian newborns, especially for lower GAs.     

Accuracy of ultrasonographic fetal weight estimation in twin pregnancies

OBJECTIVE: To compare the accuracy of fetal weight estimations between normal and growth-restricted twin and singleton pregnancies in a single tertiary center. METHODS: The computerized ultrasound database of a tertiary center was searched for all fetal weight estimations made in twin pregnancies from 2001 to 2006, which were performed up to 3 days before delivery. Accuracy was compared with a control group of singleton pregnancies at a 3:1 ratio. Estimated fetal weight was calculated by the Hadlock formula. Analyses were performed for the whole group and for pregnancies associated with fetal growth restriction and discordancy. RESULTS: The study groups included 278 twins and 834 singleton pregnancies. The twins group was characterized by a higher mean absolute percentage error compared with the singleton group (8.9% compared with 6.8%). Accuracy was lower for the second twins than for the first twins. When comparing the subgroup of fetal growth restriction, differences in sensitivity and specificity were small for singleton compared with overall twins (47.5% compared with 48.9% and 97.7% compared with 95.7%, respectively). Overall accuracy was better in the singleton group (95% compared with 88%), mainly due to relatively low accuracy in the second twin (86%). For detection of discordancy, estimated fetal weight had a sensitivity of 52%, specificity of 88%, and overall accuracy of 81%. CONCLUSION: The accuracy of the ultrasonographic estimated fetal weight seems to be lower for twin gestations than for singleton gestations, especially for second twins. These data should be considered by clinicians when making decisions based on ultrasonographic characteristics.     

Determinants and consequences of discrepancies in menstrual and ultrasonographic gestational age estimates

OBJECTIVES: To assess the association between maternal and fetal characteristics and discrepancy between last normal menstrual period and early (<20 weeks) ultrasound-based gestational age and the association between discrepancies and pregnancy outcomes. DESIGN: Hospital-based cohort study. SETTING: Montreal, Canada. SAMPLE: A total of 46,514 women with both menstrual- and early ultrasound-based gestational age estimates. MAIN OUTCOME MEASURES: Positive (last normal menstrual period > early ultrasound, i.e. menstrual-based gestational age is higher than early ultrasound-based gestational age, so that the expected date of delivery is earlier with the menstrual-based gestational age) discrepancies > or =+7 days, mean birthweight, low birthweight, stillbirth and in-hospital neonatal death. RESULTS: Multiparous mothers and those with diabetes, small stature or high pre-pregnancy body mass index were more likely to have positive discrepancies. The proportion of women with discrepancies > or =+7 days was significantly higher among chromosomally malformed and female fetuses. The mean birthweight declined with increasingly positive differences. The risk of low birthweight was significantly higher for positive differences. Associations with fetal growth measures were more plausible with early ultrasound estimates. CONCLUSIONS: Although most discrepancies between last normal menstrual period- and early ultrasound-based gestational age are attributable to errors in menstrual dating, our results suggest that some positive differences reflect early growth restriction.     

Blood glucose determinations in large for gestational age infants

Our purpose was to identify factors that may contribute to hypoglycemia in large for gestational age (LGA) infants and subsets of infants for whom blood glucose screening would be clinically helpful. LGA infants of 36 to 42 weeks of gestational age using the Denver criteria were identified from the 1999 through 2001 birth log at Marquette General Hospital, Marquette, Michigan, a rural referral hospital, for a retrospective chart review. Infants of mothers with diabetes were excluded. The impact of maternal factors, intrauterine factors, and birthweight on blood glucose levels was assessed using marginal mixed models, Poisson regression, and receiver operating characteristic curves. We found 457 infant records documented blood glucose levels among the 727 infant records analyzed. The lowest blood glucose levels occurred in the first 90 minutes of life. Blood glucose levels were positively associated with weeks of gestation and breastfeeding. Birthweight did not predict hypoglycemia in any of the multivariable models constructed. Symptoms consistent with hypoglycemia occurred only in boys and were negatively associated with gestational age. Models using prenatal and perinatal factors to predict hypoglycemia or symptomatic hypoglycemia had little clinical value. In this large community-based sample of LGA infants, we found no evidence that higher birthweight increases the risk for hypoglycemia. The clinical usefulness of routine blood glucose monitoring in healthy LGA infants is not supported by this retrospective analysis and needs to be established by prospective studies.     

Reasons for increasing trends in large for gestational age births

OBJECTIVE: To describe the magnitude of change in the proportion of term and postterm (37 completed weeks or more) large for gestational age (LGA) infants between 1992-2001 in Sweden and to examine whether time trends in prevalence of LGA births can be explained by changes in maternal risk factors. METHODS: Using the population-based Swedish Birth Register, we analyzed data from 1992 through 2001 on births of women who delivered live, singleton, term infants without malformations (N = 874,163). Unconditional logistic regression was used to model the odds of LGA birth. RESULTS: Mean birth weight and proportions of LGA births and births 4,500 g or more rose during the period 1992 to 2001. An unadjusted analysis estimated that the risk of LGA birth increased by 23% over 10 years. However, the prevalence of overweight and obesity (body mass index of 25 or greater) increased from 25% to 36%, and the prevalence of smoking decreased from 23% to 11% during the same period. After adjusting trends in all covariates simultaneously, the association between risk of LGA birth and calendar year disappeared. CONCLUSION: The increasing proportions of LGA births over time is explained by concurrent increases in maternal body mass index and decreases in maternal smoking. With the increasing prevalence of overweight among adolescents and young women, the prevalence of LGA infants and associated risks may increase over time. LEVEL OF EVIDENCE: II-2     

Glycemic control in gestational diabetes mellitus--how tight is tight enough: small for gestational age versus large for gestational age?

The relationship between optimal levels of glycemic control and perinatal outcome was assessed in a prospective study of 334 gestational diabetic women and 334 subjects matched for control of obesity, race, and parity. All women with gestational diabetes mellitus were instructed in the use of a memory-based reflectance meter. They were treated with the same metabolic goal according to a predetermined protocol. Three groups were identified on the basis of mean blood glucose level throughout pregnancy (low, less than or equal to 86 mg/dl; mid, 87 to 104 mg/dl; and high, greater than or equal to 105 mg/dl). The low group had a significantly higher incidence of small-for-gestational-age infants (20%). In contrast, the incidence of large-for-gestational-age infants was 21-fold higher in the mean blood glucose category than in the low mean blood glucose category (24% vs. 1.4%, p less than 0.0001). An overall incidence of 11% small-for-gestational-age and 12% large-for-gestational-age infants was calculated for the control group. A significantly higher incidence of small-for-gestational-age infants (20% vs. 11%, p less than 0.001) was found between the control and the low category. In the high mean blood glucose category an approximate twofold increase was found in the incidence of large-for-gestational-age infants when compared with the control group (p less than 0.03). No significant difference was found between the control and mean blood glucose categories (87 to 104 mg/dl). Our data suggest that a relationship exists between level of glycemic control and neonatal weight. This information is helpful in targeting the level of glycemic control while optimizing pregnancy outcome in gestational diabetes comparable to the general population.