Customized estimated fetal weight: a novel antenatal tool to diagnose abnormal fetal growth




Objective


We sought to apply customized standards to ultrasound-derived estimated fetal weight (EFW), and assess the frequency of abnormal growth when compared to population-based standards. We also evaluated association with adverse perinatal outcomes.


Study Design


This was a historical cohort using prenatal ultrasound examination data at ≥24 weeks over a 1-year period. Ultrasound-derived EFW and growth percentile (population-based EFW [popEFW]) were reported and compared to a customized EFW (custEFW).


Results


In all, 782 women met inclusion criteria. More fetuses were identified as small for gestational age (SGA) (15.1% vs 3.8%; P < .0001) and large for gestational age (LGA) (6.8% vs 1.7%; P < .0001) using custEFW, and adverse perinatal outcomes were more frequent among those identified by the custEFW compared to the popEFW. Both SGA and LGA diagnosed by custEFW were predictive of a neonatal SGA (positive likelihood ratio, 8.64) and LGA (positive likelihood ratio, 15.4).


Conclusion


CustEFW was a better predictor of abnormal birthweight and adverse outcomes compared to traditional popEFW standards.


Fetal growth abnormalities are associated with increased perinatal morbidity and mortality, both acute and in the long term. Consequently, the presence of abnormal fetal growth detected during prenatal ultrasound evaluation is a frequent cause of antenatal testing and a major reason for medically indicated delivery. Estimating gestational age solely by patient-reported last menstrual period is plagued with errors that contribute to inaccurate determinations of fetal growth abnormalities leading to unnecessary interventions in the late preterm and early term period. Inaccuracies in menstrual dating have led to the widespread use of ultrasound to improve the accuracy of gestational age estimation and the creation of new fetal growth curves, from which deviations are considered pathologic.


Customized growth curves that take into consideration maternal height, weight, parity, ethnicity, and fetal sex have been used to determine the expected birthweight for a pregnancy in optimal conditions. Numerous studies have demonstrated that the use of customized birthweight improves the identification of actual pathologic growth and is better correlated with adverse neonatal outcomes when compared to population-derived growth curves. In 2009, Gardosi and Francis created customized growth standards for the US population based on >30,000 pregnancies. Our hypothesis was that customized estimated fetal weight (custEFW) percentiles based on ultrasound-derived estimated fetal weight (EFW) would considerably improve the prediction of adverse perinatal outcomes.


Materials and Methods


This was a historic cohort study of women who delivered at a single tertiary hospital over a 1-year period (July 1, 2010, through June 30, 2011). A computerized perinatal database was used to identify women delivered at ≥24 weeks 0 days at Memorial Hermann Hospital–Texas Medical Center in Houston, TX. Women with multiple gestation, antepartum stillbirth, or fetal structural/chromosomal abnormalities were excluded. Study personnel reviewed maternal and neonatal hospital charts of all eligible women to obtain pertinent clinical and outcome data. In cases where women had >1 ultrasound during the pregnancy, the ultrasound latest in gestational age was included for study. Ultrasound-derived EFW was calculated utilizing the formula of Hadlock et al and the EFW percentiles (population-based EFW [popEFW]) were reported using the table devised by Williams et al. The table of Williams et al was developed from a population of >2 million births in the state of California, is used in our routine clinical practice, and only adjusts for gestational age. A customized birthweight percentile based on the US population has been described that adjusted for maternal height, weight, ethnicity, parity, and fetal sex (Bulk Centile Calculator, version 6.4 US Edition; Perinatal Institute, Birmingham, UK). In this analysis, we utilized the EFW by ultrasound parameters (formula of Hadlock et al ) and determined a custEFW using this same formula. The frequency of infants who were small for gestational age (SGA), defined as EFW <10th%ile, vs large for gestational age (LGA), defined as EFW >90th%ile, were compared between methods.


Secondary outcomes studied were SGA by customized newborn birthweight, LGA by customized newborn birthweight, preterm birth (PTB) <37 weeks, PTB <34 weeks, cesarean delivery (CD) for fetal indications, neonatal intensive care unit (NICU) admission, CD for arrested labor, and birthweight >4000 g. We then evaluated the association of ultrasound performed at 24-28 and 28-32 weeks to actual birthweight >90th%ile or <10th%ile. SPSS statistical software (PASW Stats version 18.0; IBM Corp, Armonk, NY) was used for data analysis. We calculated and reported χ 2 , sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and likelihood ratios where appropriate. This study was approved by both university and hospital institutional review boards.




Results


During the 1-year study period, there are approximately 4800 births at our institution; 782 pregnancies met the study inclusion criteria and had complete data available for analysis. There were 93 ultrasounds performed between 24-28 weeks, 168 between 28-32 weeks, 325 between 32-36 weeks, and 196 performed at >36 weeks for which outcome data were available.


The patient demographic and clinical characteristics are summarized in Table 1 . Eighty-nine fetuses were classified as SGA and 42 as LGA by only custEFW in contrast to only popEFW, which identified 1 fetus as SGA and 2 fetuses as LGA that were not identified by the custEFW. On prenatal ultrasound, more fetuses were identified as SGA using custEFW percentile compared to popEFW percentile (15.1% vs 3.8%, P < .0001; relative risk [RR], 163.2; 95% confidence interval [CI], 22.4–1186.5). Of all fetuses identified as SGA by prenatal ultrasound, 48.4% diagnosed by the custEFW percentile and 14.8% diagnosed by the popEFW percentile were ultimately diagnosed as SGA at birth (RR, 7.1; 95% CI, 5.1–9.8; and RR, 13.3; 95% CI, 5.8–30.4, respectively). All secondary outcome measures (PTB <34 weeks, PTB <37 weeks, NICU admission, and CD for fetal indications) were also more frequent among those diagnosed as SGA by custEFW percentile ( Table 2 ). Additionally, more fetuses were identified as LGA using custEFW percentile compared to popEFW percentile (6.8% vs 1.7%; P < .0001; RR, 75.7; 95% CI, 17.2–332.5). Of those fetuses identified as LGA by prenatal ultrasound, 44.6% diagnosed by the custEFW percentile and 12.5% diagnosed by the popEFW percentile were ultimately diagnosed as LGA at birth (RR, 11.6; 95% CI, 7.3–18.4; and RR, 15.1; 95% CI, 5.3–43.5, respectively). The remaining outcomes are further characterized in Table 3 . We calculated sensitivity, specificity, PPV, NPV, and likelihood ratios for outcomes, which are further described in Tables 4 and 5 .



TABLE 1

Study population characteristics




















































Characteristics n = 782
Maternal age, y 26.6 ± 6.1
Race/ethnicity
White 155 (19.8)
Black 361 (46.2)
Hispanic 209 (26.7)
Other 57 (7.3)
BMI, kg/m 2 32.6 ± 8.1
Government insurance 400 (51.2)
Birthweight, g 2961 ± 705
Nulliparity 325 (41.6)
CD 313 (40)
CD for fetal indications 87 (11.1)
Preterm birth <37 wk 192 (24.6)
Preterm birth <34 wk 65 (8.3)
NICU admission 123 (15.7)

BMI, body mass index; CD, cesarean delivery; NICU, neonatal intensive care unit.

Data presented as n (%) and mean ± SD.

Kase. Customized estimated fetal weight: diagnosing abnormal fetal growth. Am J Obstet Gynecol.


TABLE 2

Outcomes of pregnancies diagnosed as small for gestational age by population-based compared to customized estimated fetal weight centiles





























Outcome SGA by popEFW centile SGA by custEFW centile P value
PTB <37 wk, n = 192 10 (5.2%) 56 (29.2%) < .0001
PTB <34 wk, n = 65 0 (0%) 19 (29.2%) < .0001
CD for fetal indications, n = 87 8 (9.2%) 24 (27.6%) < .0001
NICU admission, n = 123 13 (10.6%) 46 (37.4%) < .0001

CD, cesarean delivery; custEFW, customized estimated fetal weight; NICU, neonatal intensive care unit; popEFW, population-based estimated fetal weight; PTB, preterm birth; SGA, small for gestational age.

Kase. Customized estimated fetal weight: diagnosing abnormal fetal growth. Am J Obstet Gynecol.


TABLE 3

Outcomes of pregnancies diagnosed as large for gestational age by population-based compared to customized estimated fetal weight centiles
























Outcome LGA by popEFW centile LGA by custEFW centile P value
Birthweight >4000 g, n = 28 6 (21.4%) 9 (32.1%) .007
Customized birthweight >90th%ile, n = 56 7 (12.5%) 25 (44.6%) .037
CD for arrested labor, n = 68 2 (2.9%) 7 (10.3%) .009

CD, cesarean delivery; custEFW, customized estimated fetal weight; LGA, large for gestational age; popEFW, population-based estimated fetal weight.

Kase. Customized estimated fetal weight: diagnosing abnormal fetal growth. Am J Obstet Gynecol.


TABLE 4

Statistical summary for comparison between population-based and customized estimated fetal weight <10th%iles



















































































Variable PopEFW <10th%ile CustEFW <10th%ile
NICU admission Sensitivity 10.6% Sensitivity 37.4%
Specificity 97.4% Specificity 89.1%
PPV 43.3% PPV 39%
NPV 85.4% NPV 88.4%
LR+ 4.1 LR+ 3.4
LR– 0.92 LR– 0.70
CD for fetal indications Sensitivity 9.2% Sensitivity 27.6%
Specificity 96.8% Specificity 86.5%
PPV 26.7% PPV 20.3%
NPV 89.5% NPV 90.5%
LR+ 2.9 LR+ 2.04
LR– 0.94 LR– 0.84
PTB <37 wk Sensitivity 5.2% Sensitivity 29.2%
Specificity 96.6% Specificity 89.5%
PPV 33.3% PPV 47.5%
NPV 75.8% NPV 79.5%
LR+ 1.54 LR+ 2.78
LR– 0.98 LR– 0.79
Sensitivity 0.8% Sensitivity 29.2%
Specificity 95.8% Specificity 86.2%
PPV 1.6% PPV 16.1%
NPV 91.3% NPV 93.1%
LR+ 0.18 LR+ 2.1
LR– 1.0 LR– 0.82

CD, cesarean delivery; custEFW, customized estimated fetal weight; LR, likelihood ratio; NICU, neonatal intensive care unit; NPV, negative predictive value; popEFW, population-based estimated fetal weight; PPV, positive predictive value; PTB, preterm birth.

Kase. Customized estimated fetal weight: diagnosing abnormal fetal growth. Am J Obstet Gynecol.


TABLE 5

Statistical summary for comparison between population-based and customized estimated fetal weight >90th%iles

































































Variable PopEFW>90th%ile CustEFW>90th%ile
Customized birthweight >90th%ile Sensitivity 12.5% Sensitivity 44.6%
Specificity 99.2% Specificity 96.1%
PPV 53.8% PPV 47.2%
NPV 93.6% NPV 95.7%
LR+ 15.1 LR+ 11.6
LR– 0.88 LR– 0.58
Birthweight >4000 g Sensitivity 21.4% Sensitivity 33.3%
Specificity 99.1% Specificity 94.2%
PPV 46.2% PPV 17%
NPV 97.1% NPV 97.5%
LR+ 23.1 LR+ 5.7
LR– 0.79 LR– 0.71
CD for arrested labor Sensitivity 2.9% Sensitivity 10.3%
Specificity 97.9% Specificity 93.5%
PPV 28.5% PPV 30.4%
NPV 78.4% NPV 80%
LR+ 1.44 LR+ 1.58
LR– 0.99 LR– 0.96

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May 15, 2017 | Posted by in GYNECOLOGY | Comments Off on Customized estimated fetal weight: a novel antenatal tool to diagnose abnormal fetal growth
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