Assessment of Gestational Age by Ultrasound | GLOWM
(gestational age, ultrasound biometry, ultrasound dating). Results were .. suggest there is no clinically important difference among confidence intervals. To assist clinicians in assigning gestational age based on ultrasound biometry. Outcomes. To determine whether ultrasound dating provides more accurate gestational The majority suggest there is no clinically important difference among. Determination of gestational age by ultrasound is a routine clinical of different dating formulae in estimating gestational age when dating was.
A Cochrane review concluded that ultrasonography can reduce the need for postterm induction and lead to earlier detection of multiple gestations 6. Because decisions to change the EDD significantly affect pregnancy management, their implications should be discussed with patients and recorded in the medical record. Measurements of the CRL are more accurate the earlier in the first trimester that ultrasonography is performed 11, 15— The measurement used for dating should be the mean of three discrete CRL measurements when possible and should be obtained in a true midsagittal plane, with the genital tubercle and fetal spine longitudinally in view and the maximum length from cranium to caudal rump measured as a straight line 8, Mean sac diameter measurements are not recommended for estimating the due date.
Dating changes for smaller discrepancies are appropriate based on how early in the first trimester the ultrasound examination was performed and clinical assessment of the reliability of the LMP date Table 1.
For example, for a day-5 embryo, the EDD would be days from the embryo replacement date. Likewise, the EDD for a day-3 embryo would be days from the embryo replacement date. Clinical Considerations in the Second Trimester Using a single ultrasound examination in the second trimester to assist in determining the gestational age enables simultaneous fetal anatomic evaluation.
Women's Health Care Physicians
With rare exception, if a first-trimester ultrasound examination was performed, especially one consistent with LMP dating, gestational age should not be adjusted based on a second-trimester ultrasound examination. Ultrasonography dating in the second trimester typically is based on regression formulas that incorporate variables such as the biparietal diameter and head circumference measured in transverse section of the head at the level of the thalami and cavum septi pellucidi; the cerebellar hemispheres should not be visible in this scanning plane the femur length measured with full length of the bone perpendicular to the ultrasound beam, excluding the distal femoral epiphysis the abdominal circumference measured in symmetrical, transverse round section at the skin line, with visualization of the vertebrae and in a plane with visualization of the stomach, umbilical vein, and portal sinus 8 Other biometric variables, such as additional long bones and the transverse cerebellar diameter, also can play a role.
Date changes for smaller discrepancies 10—14 days are appropriate based on how early in this second-trimester range the ultrasound examination was performed and on clinician assessment of LMP reliability.
Because of the risk of redating a small fetus that may be growth restricted, management decisions based on third-trimester ultrasonography alone are especially problematic; therefore, decisions need to be guided by careful consideration of the entire clinical picture and may require close surveillance, including repeat ultrasonography, to ensure appropriate interval growth. The best available data support adjusting the EDD of a pregnancy if the first ultrasonography in the pregnancy is performed in the third trimester and suggests a discrepancy in gestational dating of more than 21 days.
Conclusion Accurate dating of pregnancy is important to improve outcomes and is a research and public health imperative. As soon as data from the LMP, the first accurate ultrasound examination, or both are obtained, the gestational age and the EDD should be determined, discussed with the patient, and documented clearly in the medical record.
The American College of Obstetricians and Gynecologists, the American Institute of Ultrasound in Medicine, and the Society for Maternal—Fetal Medicine recognize the advantages of a single dating paradigm being used within and between institutions that provide obstetric care.
How Doctors Date Pregnancies, Explained
Table 1 provides guidelines for estimating the due date based on ultrasonography and the LMP in pregnancy, and provides single-point cutoffs and ranges based on available evidence and expert opinion. Fetal Imaging Workshop Invited Participants.
A comparison of recalled date of last menstrual period with prospectively recorded dates. J Womens Health Larchmt ; Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination. Am J Obstet Gynecol ; Last menstrual period versus ultrasound for pregnancy dating. Int J Gynaecol Obstet ; First trimester ultrasound screening is effective in reducing postterm labor induction rates: Ultrasound for fetal assessment in early pregnancy.
Cochrane Database of Systematic ReviewsIssue 7. Predicting delivery date by ultrasound and last menstrual period in early gestation. New charts for ultrasound dating of pregnancy and assessment of fetal growth: Ultrasound Obstet Gynecol ; First- and second-trimester ultrasound assessment of gestational age.
Methods for Estimating the Due Date - ACOG
First- vs second-trimester ultrasound: Br J Obstet Gynaecol ; Gestational age in pregnancies conceived after in vitro fertilization: Ultrasound dating at 12—14 weeks of gestation. Some women will deliver on their due date, others before, and others after.
The body is not on a clock counting down to delivery; natural variation will introduce uncertainty. Here I explain the three methods of pregnancy dating and how medical professionals use them.
Last Menstrual Period Get the facts, direct to your inbox. Subscribe to our daily or weekly digest. Logically, one might imagine we represent a pregnancy by how much time has elapsed since conception.
- Assessment of Gestational Age by Ultrasound
- How Doctors Date Pregnancies, Explained
- Methods for Estimating the Due Date
Instead, we most commonly date pregnancies from the first day of the last menstrual period LMP. One reason for not dating pregnancies from the day of conception is that we cannot know that day exactly excluding cases of assisted reproductionbut we can know the first day of LMP, based on what a patient reports to us. Also, when providers all use the same LMP date, we are using one system that provides a standard convention. The average time between menstrual periods is about 28 days, and ovulation occurs about 14 days before the next period begins.Gestational Age Vs. Fetal Age
The expected duration of a pregnancy is 40 weeks from the first day of LMP four weeks more than the traditional nine months by which many count. It is not used by medical professionals to describe pregnancy length and is solely a political term. Sometimes we do use a trimester system if we are seeking to describe how far along a woman is in general terms. Trimesters, however, have a variability of a few weeks, so they should be thought of as general benchmarks.
The first trimester is generally considered to comprise the time up to 12 or 14 weeks from the LMP.