- Email: [email protected]
Last menstrual period versus ultrasound for pregnancy dating
International Journal of Gynecology and Obstetrics (2004) 87, 38 -- 39
www.elsevier.com/locate/ijgo
BRIEF COMMUNICATION
Last menstrual period versus ultrasound for pregnancy datingB W.B. Barra,*, C.C. Peccib a
Department of Family Practice and Community Medicine and Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania, Philadelphia, PA 19104, USA b Tufts University School of Medicine and Greater Lawrence Family Health Center, Lawrence, MA, USA Received 23 December 2004; received in revised form 10 June 2004; accepted 21 June 2004
KEYWORDS Gestational age; Ultrasonography; Prenatal; Hispanic--Americans; Last menstrual period
Most clinical decisions during pregnancy are influenced by the presumed gestational age of the fetus at the time decisions need to be made. As there is no direct method to calculate gestational age, we approximate it by calculating the estimated date of delivery (EDD). In several large studies, the EDD calculated during a second trimester ultrasound was more accurate than an EDD based on a reliable last menstrual period (LMP) [1--3], but these studies did not include Latinas. Since ultrasound anthropometric measurements could differ by B Presented at the North American Primary Care Research Group (NAPCRG) 2002 Annual Meeting, November 17--20, 2002, New Orleans, LA, USA. * Corresponding author. Tel.: +1-215-615-3818; fax: +1-215662-3591. E-mail address: [email protected] (W.B. Barr).
ethnic group, there is need for investigating whether the findings from these large studies could be applied to other ethnicities [4]. A retrospective within-subject matched pair cohort design was used to compare EDD calculated based on second trimester ultrasound (12--24 weeks) to that calculated based on a reliable LMP in a mostly Caribbean Latina sample of 109 patients. The demographic and potential confounding variables for the sample are shown in Table 1. The primary outcome measure was the absolute difference between the actual date of delivery and the EDD for each method. Table 2 shows the descriptive statistics for the absolute differences and the results of the Wilcoxon Paired
Table 1
Characteristics of study sample
N Age (mean) Gravity (mean) Parity (mean) Hispanic (%) Smokers (%) Public or no insurance (%) Inductions (%)
109 23.4 2.3 1.0 86.2 9.3 62.4 4.6
0020-7292/$ - see front matter D 2004 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ijgo.2004.06.008
Last menstrual period versus ultrasound for pregnancy dating Table 2 A comparison of the absolute difference in days between the actual date of delivery (DOD) and the estimated date of delivery (EDD) calculated from LMP and U/S Median difference Inter quartile range Wilcoxon ( P-value)
LMP
Ultrasound
7.0 2--12 b0.001
5.0 2--8
Rank-Sum Test. Ultrasound-based EDD had significantly less difference in days than LMP from the actual date of delivery ( Pb0.001). Previous studies had found similar results with larger samples but none included a significant proportion of Latinas in their sample [1--3]. This is of increasing importance to have external validity in the United States where Latinos are now the largest and fastest growing minority group. This study also finds that Naegle’s Rule is not simply less accurate than second trimester ultrasound but is also less reliable (as measured by interquartile ranges) and therefore Naegle’s Rule can not be improved by simply adding 2--3 days to the EDD. LMP has long been considered the standard for establishing the EDD, but this study and others find that second trimester ultrasound is more accurate.
39
This could lead to the argument that second trimester ultrasounds are adequate to establish an accurate EDD and therefore a first trimester ultrasound is not necessary when the LMP is unknown or unreliable (as was the case in approximately half of the initial study sample). This would allow for more efficient use of medical resources by combining both a dating ultrasound and anatomic fetal survey in one optimally timed scan.
References [1] Mongelli M, Wilcox M, Gardosi J. Estimating the date of confinement: ultrasonographic biometry versus certain menstrual dates. Am J Obstet Gynecol 1996;174:278 -- 81. [2] Waldenstrom U, Axelsson O, Nilsson S. A comparison of the ability of a sonographically measured biparietal diameter and the last menstrual period to predict the spontaneous onset of labor. Obstet Gynecol 1990;76:336 -- 8. [3] Savitz DA, Terry JW, Dole N, Thorp JM, Siega-Riz AM, Herring AH. Comparison of pregnancy gating by last menstrual period, ultrasound scanning, and their combination. Am J Obstet Gynecol 2002;187:1660 -- 6. [4] Wilcox M, Gardosi J, Mongelli M, Ray C, Johnson I. Birth weight from pregnancies dated by ultrasonography in a multicultural British population. Br Med J 1993;307:588 -- 91.
www.elsevier.com/locate/ijgo
BRIEF COMMUNICATION
Last menstrual period versus ultrasound for pregnancy datingB W.B. Barra,*, C.C. Peccib a
Department of Family Practice and Community Medicine and Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania, Philadelphia, PA 19104, USA b Tufts University School of Medicine and Greater Lawrence Family Health Center, Lawrence, MA, USA Received 23 December 2004; received in revised form 10 June 2004; accepted 21 June 2004
KEYWORDS Gestational age; Ultrasonography; Prenatal; Hispanic--Americans; Last menstrual period
Most clinical decisions during pregnancy are influenced by the presumed gestational age of the fetus at the time decisions need to be made. As there is no direct method to calculate gestational age, we approximate it by calculating the estimated date of delivery (EDD). In several large studies, the EDD calculated during a second trimester ultrasound was more accurate than an EDD based on a reliable last menstrual period (LMP) [1--3], but these studies did not include Latinas. Since ultrasound anthropometric measurements could differ by B Presented at the North American Primary Care Research Group (NAPCRG) 2002 Annual Meeting, November 17--20, 2002, New Orleans, LA, USA. * Corresponding author. Tel.: +1-215-615-3818; fax: +1-215662-3591. E-mail address: [email protected] (W.B. Barr).
ethnic group, there is need for investigating whether the findings from these large studies could be applied to other ethnicities [4]. A retrospective within-subject matched pair cohort design was used to compare EDD calculated based on second trimester ultrasound (12--24 weeks) to that calculated based on a reliable LMP in a mostly Caribbean Latina sample of 109 patients. The demographic and potential confounding variables for the sample are shown in Table 1. The primary outcome measure was the absolute difference between the actual date of delivery and the EDD for each method. Table 2 shows the descriptive statistics for the absolute differences and the results of the Wilcoxon Paired
Table 1
Characteristics of study sample
N Age (mean) Gravity (mean) Parity (mean) Hispanic (%) Smokers (%) Public or no insurance (%) Inductions (%)
109 23.4 2.3 1.0 86.2 9.3 62.4 4.6
0020-7292/$ - see front matter D 2004 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.ijgo.2004.06.008
Last menstrual period versus ultrasound for pregnancy dating Table 2 A comparison of the absolute difference in days between the actual date of delivery (DOD) and the estimated date of delivery (EDD) calculated from LMP and U/S Median difference Inter quartile range Wilcoxon ( P-value)
LMP
Ultrasound
7.0 2--12 b0.001
5.0 2--8
Rank-Sum Test. Ultrasound-based EDD had significantly less difference in days than LMP from the actual date of delivery ( Pb0.001). Previous studies had found similar results with larger samples but none included a significant proportion of Latinas in their sample [1--3]. This is of increasing importance to have external validity in the United States where Latinos are now the largest and fastest growing minority group. This study also finds that Naegle’s Rule is not simply less accurate than second trimester ultrasound but is also less reliable (as measured by interquartile ranges) and therefore Naegle’s Rule can not be improved by simply adding 2--3 days to the EDD. LMP has long been considered the standard for establishing the EDD, but this study and others find that second trimester ultrasound is more accurate.
39
This could lead to the argument that second trimester ultrasounds are adequate to establish an accurate EDD and therefore a first trimester ultrasound is not necessary when the LMP is unknown or unreliable (as was the case in approximately half of the initial study sample). This would allow for more efficient use of medical resources by combining both a dating ultrasound and anatomic fetal survey in one optimally timed scan.
References [1] Mongelli M, Wilcox M, Gardosi J. Estimating the date of confinement: ultrasonographic biometry versus certain menstrual dates. Am J Obstet Gynecol 1996;174:278 -- 81. [2] Waldenstrom U, Axelsson O, Nilsson S. A comparison of the ability of a sonographically measured biparietal diameter and the last menstrual period to predict the spontaneous onset of labor. Obstet Gynecol 1990;76:336 -- 8. [3] Savitz DA, Terry JW, Dole N, Thorp JM, Siega-Riz AM, Herring AH. Comparison of pregnancy gating by last menstrual period, ultrasound scanning, and their combination. Am J Obstet Gynecol 2002;187:1660 -- 6. [4] Wilcox M, Gardosi J, Mongelli M, Ray C, Johnson I. Birth weight from pregnancies dated by ultrasonography in a multicultural British population. Br Med J 1993;307:588 -- 91.