Abstract
Estimating gestational age in resource-limited settings is prone to considerable inaccuracy because crown-rump length measured by ultrasound before 14 weeks gestation, the recommended method for estimating gestational age, is often unavailable. Judgements regarding provision of appropriate obstetric and neonatal care are dependent on accurate estimation of gestational age. We determined the accuracy of the Dubowitz Gestational Age Assessment, a population-specific symphysis-fundal height formula, and ultrasound biometry performed between 16 and 40 weeks gestation in estimating gestational age using pre-existing data from antenatal clinics of the Shoklo Malaria Research Unit on the Thai-Myanmar border, where malaria is endemic. Two cohorts of women who gave birth to live singletons were analysed: 1) 250 women who attended antenatal care between July 2001 and May 2006 and had both ultrasound crown-rump length (reference) and a Dubowitz Gestational Age Assessment; 2) 975 women attending antenatal care between April 2007 and October 2010 who had ultrasound crown-rump length, symphysis-fundal measurements, and an additional study ultrasound (biparietal diameter and head circumference) randomly scheduled between 16 and 40 weeks gestation. Mean difference in estimated newborn gestational age between methods and 95% limits of agreement (LOA) were determined from linear mixed-effects models. The Dubowitz method and the symphysis-fundal height formula performed well in term newborns, but overestimated gestational age of preterms by 2.57 weeks (95% LOA: 0.49, 4.65) and 3.94 weeks (95% LOA: 2.50, 5.38), respectively. Biparietal diameter overestimated gestational age by 0.83 weeks (95% LOA: -0.93, 2.58). Head circumference underestimated gestational age by 0.39 weeks (95% LOA: -2.60, 1.82), especially if measured after 24 weeks gestation. The results of this study can be used to quantify biases associated with alternative methods for estimating gestational age in the absence of ultrasound crown-rump length to inform critical clinical judgements in this population, and as a point of reference elsewhere.
Highlights
Accurate determination of gestational age (GA) is essential for the provision of appropriate obstetric and neonatal care, including treatment of infections during pregnancy with drugs that may be contraindicated in the first trimester, detection of growth restriction and postterm pregnancies (!42 weeks gestation), provision of antenatal corticosteroids during preterm labour, and decisions regarding whether to administer or withhold intensive care to extremely premature infants [1,2,3,4]
Overlays of the distributions of newborn GA estimated from each method indicate overestimation of GA by the Dubowitz method, the Symphysis-pubis fundal height (SFH) formula, and biparietal diameter (BPD) biometry, and underestimation of GA by head circumference (HC) biometry in reference to crown-rump length (CRL) biometry estimates (S1 Fig)
Linear mixed-effects models were fitted to determine the level of agreement between CRL biometry and the Dubowitz method, SFH formula, and HC/BPD biometry in estimating newborn GA
Summary
Accurate determination of gestational age (GA) is essential for the provision of appropriate obstetric and neonatal care, including treatment of infections during pregnancy with drugs that may be contraindicated in the first trimester, detection of growth restriction and postterm pregnancies (!42 weeks gestation), provision of antenatal corticosteroids during preterm labour, and decisions regarding whether to administer or withhold intensive care to extremely premature infants [1,2,3,4]. Fetal crown-rump length (CRL) measured by ultrasound between 7+0 and 13+6 weeks gestation is the recommended method for precise dating of spontaneously conceived pregnancies [5]. Beyond 14 weeks, ultrasound up to 24 weeks is the upper recommended limited for accurate dating using other fetal biometry measurements including head circumference (HC) and biparietal diameter (BPD) [5]. While several publications have demonstrated successful sonography in resource-limited settings, quality routine ultrasound is rarely available [6,7,8]. Late attenders to antenatal care or birth centres present dating issues in all settings because ultrasound biometry is less accurate and less precise when measured later during pregnancy [9,10,11]. Estimating gestational age in the absence of CRL biometry is a problem of global significance
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