When LMP and Ultrasound Dates Don’t Match: When to Redate?

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Most often used during the early stages of pregnancy. In these cases, a pregnancy wheel can still be used, but some simple calculations are necessary. Review by Mark Curran, M.

Your doctor may change your due date if your fetus is significantly smaller or larger than the average fetus at your particular stage of pregnancy. The LMP is used because most women know when their last period was, but may not know when they actually conceived. Request an appointment First Name required Last Name required Your Email Your Phone Please contact me by: required Email Phone Either I want to schedule an appointment for: Pregnancy Testing: First date of last period: Pregnancy dating by ultrasound A positive pregnancy test must be confirmed at Blue Ridge Women's Center to schedule an ultrasound.

How to Calculate Your Due Date

Calculate estimated due date EDD and gestational age based on : Conception date date of ovulation, egg retrieval, or insemination Date of 3-day embryo transfer Date of 5-day embryo blast transfer Due date by sonogram reverse calculation First day of last menstrual period See Also Determining the Date of Conception Because the human egg is capable of fertilization for only 12 to 24 hours after ovulation the date of ovulation may be taken as being the date of conception. However, ultrasound determination of the date of ovulation has the same imprecision as does the ultrasound estimate of the gestational age and, therefore, a precise date of conception cannot usually be determined as with in vitro fertilization. Determining the Estimated Due Date The estimated due date EDD or EDC is the date that spontaneous onset of labor is expected to occur. The due date may be estimated by adding 280 days 9 months and 7 days to the first day of the last menstrual period LMP. The accuracy of the EDD derived by this method depends on accurate recall by the mother, assumes regular 28 day cycles, and that ovulation and conception occurs on day 14 of the cycle. In cases where the date of conception is known precisely, such as with in vitro fertilization, the EDD is calculated by adding 266 days to the date of conception. Ultrasound uses the size of the fetus to determine the gestational age the time elapsed since the the first day of the last menstrual period. The accuracy of the ultrasound estimate of the gestational age varies according to the gestational age. The gestational age should ,therefore, be at least 10 to 12 weeks if fetal heart tone are heard. The gestational age would, therefore, be at least 3 to 4 weeks at the time of a reliable hCG pregnancy test. Twins When a twin pregnancy is the result of in vitro fertilization determination of gestational age should be made from the date of embryo transfer. The tendency for multiple gestations to be delivered earlier than singleton pregnancies should not be interpreted that multiples should be assigned an earlier estimated due date. Review by Mark Curran, M. Chervenak FA, Skupski DW, Romero R, et al: How accurate is fetal biometry in the assessment of fetal age?. Am J Obstet Gynecol 1998; 178:678. Mongelli M, Wilcox M, Gardosi J. Am J Obstet Gynecol 1996; 174:278. Savitz DA, Terry Jr JW, Dole N, et al: Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination. Am J Obstet Gynecol 2002; 187:1660. Clinical management guidelines for obstetricians-gynecologists. Number 55, September 2004 replaces practice pattern number 6, October 1997. Management of Postterm Pregnancy. Kramer MS, McLean FH, Boyd ME, Usher RH: The validity of gestational age estimation by menstrual dating in term, preterm and postterm gestations. Savitz DA, Terry JW Jr, Dole N, Thorp JM Jr, Siega-Riz AM, Herring AH. Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination. Am J Obstet Gynecol. Wilcox M, Gardosi J, Mongelli M, et al. Birth weight from pregnancies dated by ultrasonography in a multicultural British population. Sep 4 1993;307 6904 :588-91. ACOG Practice Bulletin No. American College of Obstetricians and Gynecologists. Obstet Gynecol 2008;112: 1419—44. Rossavik IK, Fishburne JI. Conceptional age, menstrual age, and ultrasound age: a second-trimester comparison of pregnancies of known conception date with pregnancies dated from the last menstrual period. Henderson SO, Mallon WK. Emerg Med Clin North Am. Hay DL, Lopata A. Chorionic gonadotropin secretion by human embryos in vitro. J Clin Endocrinol Metab. Wilcox AJ, et al. Time of implantation of the conceptus and loss of pregnancy. N Engl J Med. Lohstroh P, et al. Daily immunoactive and bioactive human chorionic gonadotropin profiles in periimplantation urine samples. ACOG Practice Bulletin No. The American College of Obstetricians and Gynecologists. Berghella V, et al. Ultrasound Obstet Gynecol 2003;21:140-144. ACOG Practice Bulletin No. American College of Obstetricians and Gynecologists. Obstet Gynecol 2009;113: 451—61. Prevention of Rh D alloimmunization. Number 4, May 1999 replaces educational bulletin Number 147, October 1990. Clinical management guidelines for obstetrician-gynecologists. American College of Obstetrics and Gynecology. Int J Gynaecol Obstet. ACOG Practice Bulletin No. American College of Obstetricians and Gynecologists. Obstet Gynecol 2008;112: 717—26 19. Number 9, October 1999 replaces Technical Bulletin Number 188, January 1994. Clinical management guidelines for obstetrician-gynecologists. Int J Gynaecol Obstet. Institute for Clinical systems Improvement. American College of Obstetricians and Gynecologists. ACOG Practice Bulletin No. Morin L, Lim K. Ultrasound in twin pregnancies. J Obstet Gynaecol Can. Sperling L, Tabor A. Twin pregnancy: the role of ultrasound in management. Acta Obstet Gynecol Scand. Method for estimating due date. Ameri-can College of Obstetricians and Gynecologists. Allen J Wilcox, David Dunson, and Donna Day Baird. Wilcox AJ, Weinberg CR, Baird DD. Timing of sexual intercourse in relation to ovulation. Effects on the probability of conception, survival of the pregnancy, and sex of the baby. N Engl J Med. Determination of Gestational Age by Ultrasound No. J Obstet Gynaecol Can 2014;36 2 :171—181 29. Martin JA, et al. Natl Vital Stat Rep. Multifetal gestations: twin, triplet, and higher-order multifetal pregnancies. American College of Obstetricians and Gynecologists. Page JM, The risk of stillbirth and infant death by each additional week of expectant management in twin pregnancies. Am J Obstet Gynecol. Epub 2015 Mar 19. Burgess JL, Unal ER, Nietert PJ, Newman RB. Risk of late-preterm stillbirth and neonatal morbidity for monochorionic and dichorionic twins. Am J Obstet Gynecol. Epub 2014 Mar 5. Definition of term pregnancy. American College of Obstetricians and Gynecologists. Obstet Gynecol 2013;122:1139—40 All calculations must be confirmed before use. The suggested results are not a substitute for clinical judgment. Copyright © 2009-2018 by Focus Information Technology. This material may not be republished, broadcast, rewritten or redistributed.

Natl Vital Stat Rep. The north date is based on the ultrasound measurements. Ultrasound is safe for you and your baby when done by your health care provider. Call 540-362-4357 if you have any questions regarding this. An ultrasound is generally performed for all pregnant women around 20 weeks into her pregnancy. Per completing this activity, the participant should be better able to: 1.