Introduction: Gestational age (GA) refers to age of an unborn baby. Accurate determination of GA is crucial as precise calculation of GA helps reducing post-date labor induction and is particularly useful to assess viability in premature labor and in post-date deliveries.
Aim: The aim of the article was to determine GA by a minimal number of fetal parameters along with greater accuracy.
Materials and methods: This was a prospective cross-sectional study, comprising a total of 229 singleton pregnant mothers enrolled from December 2015 to November 2016 in Ibn Sina Diagnostic and Imaging Center and Ad-Din Hospital in Dhaka, Bangladesh. Multiple linear regression models were fitted with four fetal parameters, namely biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL), and lack of fit was tested in each of the cases. In case of having a significant lack of fit, different types of transformation including Box-Cox transformation have been adopted on the variables to improve the adequacy of the model.
Results: Among all the fitted models for gestational age by last menstrual period (GALMP), a model with a single explanatory variable, BPD, was found to be comparatively better than others. The Box-Cox transformation was taken on the dependent variable GALMP with λ that equals 0.2, and lack of fit test was not significant at 1% level (p-value = 0.027). Though the results from comparative models do not vary substantially, emphasis on BPD in GA calculation might suffice while cost of experimentation or screening is a grave concern.
Conclusion: By considering the Box-Cox transformation and proper dealing of outliers, a model for GALMP was obtained without lack of fit where only the BPD appeared to be sufficient as an explanatory variable.
Machado L, Vaclavinkova V, Gibb H. Evaluation of applicability of standard growth curves to healthy native Omani women by fetal biometry at selected gestational ages. Sultan Qaboos Univ Med J [SQUMJ] 2000;2(2):97–104. https://journals.squ.edu.om/index.php/squmj/article/view/1203.
Shehzad K, Ali M, Zaidi S. Fetal biometry. Pak J Med Sci 2006;22(4):503. https://pjms.com.pk/issues/octdec06/pdf/fetal_biometry.pdf.
Butt K, Lim K, Bly S, et al. Determination of gestational age by ultra-sound. J Obstet Gynaecol Can 2014;36(2):171–181. DOI: 10.1016/S1701-2163(15)30664-2.
Konje J, Abrams K, Bell S, et al. Determination of gestational age after the 24th week of gestation from fetal kidney length measurements. Ultrasound Obstet Gynecol 2002;19(6):592–597. DOI: 10.1046/j.1469-0705.2002.00704.x.
Zaidi S, Shehzad K, et al. Sonographic foetal measurements in a cohort of population of Karachi, Pakistan. JPMA 2009;59(4):246–249. https://www.jpma.org.pk/PdfDownload/1676.pdf.
Benson C, Doubilet P. Sonographic prediction of gestational age: accuracy of second-and third-trimester fetal measurements. AJR 1991;157(6):1275–1277. DOI: 10.2214/ajr.157.6.1950881.
Chervenak FA, Skupski DW, Romero R, et al. How accurate is fetal biometry in the assessment of fetal age? Am J Obstet Gynecol 1998;178(4):678–687. DOI: 10.1016/s0002-9378(98)70477-6.
Mailath-Pokorny M, Polterauer S, Worda K, et al. Isolated short fetal femur length in the second trimester and the association with adverse perinatal outcome: experiences from a tertiary referral center. PLoS One 2015;10(6):e0128820. DOI: 10.1371/journal.pone.0128820.
Rahman ML, Sultana A, Das K. Determination of gestational age: a perspective with the Bangladeshi ethnicity. Eur Sci J 2018;14(6):375–386. DOI: 10.19044/esj.2018.v14n6p375.
Box GE, Cox DR. An analysis of transformations. J R Stat Soc 1964;26(2):211–243. http://links.jstor.org/sici?sici=0035-9246%281964%2926%3A2%3C211%3AAAOT%3E2.0.CO%3B2-6.
Neter J, Kutner MH, Nachtsheim CJ, et al. Applied linear statistical models, vol. 4. Chicago: Irwin; 1996.
Yan X, Su X. Linear regression analysis: theory and computing. World Scientific; 2009. DOI: 10.1142/6986.
Jaiswal P, Masih WF, Jaiswal S, et al. Assessment of fetal gestational age by ultrasonic measurement of bi-parietal diameter in the southern part of Rajasthan. Med J Dr DY Patil Univ 2015;8(1):27. DOI: 10.4103/0975-2870.148839.
Kurtz AB, Wapner RJ, Kurtz RJ, et al. Analysis of biparietal diameter as an accurate indicator of gestational age. J Clin Ultrasound 1980;8(4):319–326. DOI: 10.1002/jcu.1870080406.
Hadlock FP, Harrist R, Deter RL, et al. Fetal femur length as a predictor of menstrual age: sonographically measured. Am J Roentgenol 1982;138(5):875–878. DOI: 10.2214/ajr.138.5.875.
Kramer MS, McLean FH, Boyd ME, et al. The validity of gestational age estimation by menstrual dating in term, preterm, and postterm gestations. JAMA 1988;260(22):3306–3308. DOI:10.1001/jama.1988.03410220090034.
Sultana A, Rahman ML. Ultrasonographic estimation of fetal gestational age by biparietal diameter: a cross sectional study in an urban area of Bangladesh. J Med Sci Clin Res 2018;6(4):1144–1151. DOI: 10.18535/jmscr/v6i4.187.