A Prospective Study on Correlation of First Trimester Crown-Rump Length With Birth Weight

Background Ultrasound examination has been a crucial part of the evaluation of fetal health during pregnancy. It has become more accurate over the past few decades as a result of advances in radiodiagnostic imaging. While obstetric ultrasonography in the first trimester has been utilized extensively for gestational age assessment and confirmation of fetal viability, the imaging technique has seen little exposure in predicting pregnancy outcomes. This study was thus undertaken to find out any possible association between one of the first trimester parameters, i.e. crown-rump length (CRL) noted at the beginning of a pregnancy, and the birth weight of the neonate. Methods This prospective cohort study conducted at a teaching hospital in India spanning over a period of eighteen months included women with a spontaneously conceived intrauterine pregnancy at six to ten weeks period of gestation as calculated from the last menstrual period. Transvaginal sonography was performed for all such women and the CRL was noted. These CRL values were then compared to a standard nomogram and assigned to either of three categories i.e. CRL <5(th) centile, 5(th )to 95(th) centile, or >95(th) centile. The women were then followed up at the hospital with standard care till the end of their pregnancy, and finally, the birth weights were noted. Data were recorded in an MS Excel spreadsheet program and analysis was performed with regard to CRL in the first trimester and birth weights using SPSS v23 (IBM Corp.). Results Crown-rump lengths and birth weights of 104 cases were evaluated. The mean age of the study population was 26.6 years and the mean period of gestation (weeks) was 8.28 ± 1.01. The incidence of low birth weight (LBW) in the study was 22.1%. The distribution of LBW was significantly different between the three CRL categories (χ2 = 15.868, p = <0.001), being considerably higher in the CRL <5(th) centile category. No embryos with CRL >95(th) centile had low birth weight. Conclusions Our study suggested a congruence between the crown-rump length of an embryo noted in the first trimester and its weight at birth, with low birth weight being a fairly common occurrence in the deficient CRL category. This study highlights the role of a carefully performed first-trimester ultrasound examination in possibly predicting an adverse pregnancy outcome such as low birth weight and the probable inherent tendency of growth restriction in fetuses that are destined to develop the same.