MATERNO-FETAL MEDICINE The significance of fetal sacral length in the ultrasonographic assessment of gestational age Mustafa Ozat • Mine Kanat-Pektas • Tayfun Gungor • Beril Gurlek • Mete Caglar Received: 20 March 2010 / Accepted: 3 May 2010 / Published online: 19 May 2010 Ó Springer-Verlag 2010 Abstract Objective The present study aims to establish a more sensitive nomogram of fetal sacral length measurements, as well as to specify the accuracy of fetal sacral length for the ultrasonographic assessment of gestational age. Methods The present study investigated a total of 2,184 pregnant women who were referred for routine pregnancy follow-up. All of the reviewed women had uncomplicated singleton pregnancies without known structural and chro- mosomal fetal anomalies. Results A statistically significant linear relationship was established between sacrum length and gestational age [gestational age = 4.49 ? 0.92 9 sacrum length (r = 0.98, R 2 = 0.96)]. The rate of increase in sacrum length of fetuses with a gestational age of \ 28 weeks was formulated as [gestational age =-0.05 ? 1.01 9 sacrum length (r = 0.96, R 2 = 0.98)], while the same formula was [gestational age = -0.09 ? 1.32 9 sacrum length (r = 0.94, R 2 = 0.96)] for fetuses with a gestational age of C28 weeks. On the other hand, a statistically significant correlation was found to exist between biparietal diameter (r = 0.68, P = 0.001), head circumference (r = 0.590, P = 0.001), femur length (r = 0.719, P = 0.001) and sacrum length (r = 0.696, P = 0.001). However, the same statistically significant correlation exists between abdominal circumference and the other sono- graphic measurements (r = 0.223, P = 0.375). Conclusions The fetal sacral length appears as an easily acquired and valuable parameter, which directly and strongly correlates with gestational age and other biomet- rical measurements. Therefore, fetal sacral length may be utilized as a complementary tool in both the evaluation of fetal growth and prediction of gestational age. Further research is required to determine the significance of fetal sacral length in prenatal follow-up. Keywords Fetal sacral length Á Gestational age Á Ultrasonography Introduction Gestational age is the age of a conceptional product, which is often expressed in weeks. Gestational age is calculated by counting from the first day of the last menstrual period or from 14 days before the date of fertilization. The latter method of calculation is based on the assumption that fertilization occurs 14 days after the first day of the last menstrual period, and hence it is also called conceptional age [1]. Gestational age is of high importance in the evaluation of fetal growth and development. However, gestational age calculations according to the last menstrual period can be biased since the average ovulation date varies physiologi- cally. The recalling ability of women may confound the reliability of these calculations as well [2–4]. Although the method of calculating gestational age with the last men- strual period is mostly convenient, other methods have been proposed for more accurate estimation [5]. Obstetric ultrasonography is the most popular of these techniques, because it allows the physicians to examine the fetal body in detail. During the last three decades, ultra- sonography of a number of fetal osseous structures have been adopted for the assessment of gestational age and the M. Ozat Á M. Kanat-Pektas (&) Á T. Gungor Á B. Gurlek Á M. Caglar Department of Perinatology, Dr. Zekai Tahir Burak Women Health Research and Education Hospital, Yunus Emre Mah, Dereboyu Sok. No: 71/2 Yenimahalle, 06170 Ankara, Turkey e-mail: minekanat@hotmail.com 123 Arch Gynecol Obstet (2011) 283:999–1004 DOI 10.1007/s00404-010-1510-5