BELIEVE MIDWIFERY SERVICES, LLC

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1 , LLC TITLE: ESTABLISHING the GESTATIONAL AGE & ROUTINE ULTRASOUND EFFECTIVE DATE: November 11th, 2013 POLICY STATEMENT Establishing accurate pregnancy dating impacts the management of normal and abnormal pregnancies and thus is one of the most important responsibilities of prenatal care providers. Accurate dating is essential for timing tests such as prenatal screening tests for aneuploidy, assessment of proper fetal growth and maturity and management of the pregnancy past the due date. Common usage of the term gestational age refers to menstrual age that equals conceptional age plus 14 days. Currently, the gestational age is assessed by menstrual history, clinical examination, ultrasound or by a known conceptional date. Gestational age is most accurately established by a certain conception date as occurs with reproductive technologies, single intercourse associated conceptions and basal body temperature records, each of which is highly predictive of conceptional age. The next most accurate assessment of menstrual age is by a six to eleven-week crown-rump length measurement by ultrasound followed by a certain last menstrual period in women with regular cycles, then by early second-trimester sonographic examinations and then first trimester followed by second-trimester physical examination. Dating the pregnancy by menstrual history or clinical examination is subject to considerable error. The mother s initial detection of fetal movements and late pregnancy ultrasound are too unreliable to be useful for accurate assessment of the gestational age. BLOOD BORNE PATHOGEN EXPOSURE CATEGORY: II (Involves no exposure to blood, body fluids, or tissues) FUNCTION: Care of Clients EQUIPMENT: 1. Gestational wheel 2. Ultrasound POINTS OF EMPHASIS: Menstrual Dating Frederich Naegele, a 19th-century obstetrician, is credited with developing a simple calculation to determine the EDD by adding 7 days to the first day of the LMP and then subtracting 3 months. This calculation, commonly referred to as Naegele s rule, establishes an EDD that is more or less 280 days from the LMP depending on which calendar months are involved. Because ovulation is not an easily observed event, using Naegele s rule provides an indirect measure of conception and remains the current standard for calculating the EDD based on the first day of the LMP. The reliability of this method depends on several factors: the woman s accurate recall of her LMP; the regularity of her cycles; the presence of early or light bleeding; and other factors, such as oral contraceptive use or breastfeeding that could influence ovulation timing. Interestingly, no recent studies have been found examining the length of human gestation; however, past sources have reported data that suggest human gestation lasts up to 7 days longer than the presumed 280 days. These results support the findings of Baird et al., Wilcox et al., and Nakling et al., which suggest that Naegele s rule does not correlate reliably with the date of conception despite the accuracy of the reported LMP. Errors in LMP Recall Even with the most careful questioning by well-intended nurses, physicians and midwives, there can be considerable errors in a woman s LMP recall, further adding to the dubiousness of this time-honored rule. For example, in a review of more than 43,000 birth records, Walker et al. found that women were more likely to report their LMP as occurring on one of seven preferred days with 15 being the most reported LMP date across all socioeconomic and ethnic groups. The authors attributed this unexpected finding to recall rounding, which would most likely lead to overestimating the gestational age, especially when compared to early ultrasound dating. The Role of Pregnancy Wheels

2 PRACTICE GUIDELINE Page 2 of 7 These wheels are primarily manufactured by drug companies and are used extensively in obstetrics to calculate both the EDD and gestational age. Despite their convenience and widespread use, there can be up to a 5-day difference between wheels, and surprisingly few research studies have addressed this inconsistency, with non showing any evidence of manufacturer quality control. In addition, pregnancy wheels typically do not correlate with Naegele s rule. McParland and Johnson also reported the added likelihood of inaccurate readings caused by misalignment from the central mounting on the wheel and the presence of unevenly spaced lines, making these wheels notoriously hard to read. It is unclear why the continued use of pregnancy wheels is still so pervasive, especially because there are now several readily available computer-based systems using actual calendar dates that are free for use by anyone with a computer that can use the software. Ross concludes that until a more acceptable and consistent method is developed to determine gestational age, obstetric providers should be aware of these potential inaccuracies and carefully evaluate the accuracy and reliability of their current dating techniques. Naegele s Rule Revisited One last caveat in regard to the issues raised with menstrual dating can be found in Basket and Naegele s1 review of Frederich Naegele s original 19th-century German obstetrics textbook. These authors1 discovered that the centuries-old Naegele s rule was in fact not Naegele s original idea but based on the writings of Hermann Boerhaave, an 18th-century professor of botany and medicine in the Netherlands. Naegele credited Boerhaave with developing the formula to calculate the delivery date from the last menses, which some historians believe Boerhaave loosely based on observations found in the Bible that human gestation lasted 10 lunar months (280 days). Later textbooks of obstetrics and gynecology in the early 20th century began crediting Naegele with this rule, and it has been unquestionably handed down as the standard for pregnancy dating ever since. What remains unclear in the translation and review of both Naegele s and Boerhaave s writings; however, is whether the calculation was meant to start from the beginning or the end of the last menses. Defining Naegele s rule as specifically starting from the first day of the LMP was thought to have originated in some of the early American obstetric textbooks and was never specified as such in Naegele s original writings. In response to this concern, Baskett and Naegele suggest that Naegele and Boerhaave were possibly misinterpreted and that the calculation might have more reliability when compared to ultrasound dating if counting began at the end of the menses or 10 days were added to the first day of the LMP instead of the standard 7 days used today when doing the calculation. As technology advances and more and more women receive ultrasound testing in pregnancy, it remains to be seen whether Naegele s rule, regardless of its original inception, will continue to stand the test of time. Ultrasound Dating A large randomized control study published in 1993, the Routine Antenatal Diagnostic Imaging with Ultrasound Study (RADIUS), found no clinical benefit to routine ultrasound screening in pregnancy. They further concluded that the costs associated with routine screening were too prohibitive to justify its use in the absence of clear medical indications. Most experts concur however, that an ultrasound performed before 24 weeks gestation establishes a more accurate EDD than relying solely on the LMP. Several studies have demonstrated a decrease in postterm induction rates when gestational age has been established by ultrasound. When one also considers the costs of postterm surveillance, which typically includes twice weekly nonstress tests and weekly amniotic fluid measurements, there are potential cost savings with accurate dating by early ultrasound assessment not to mention the costs of fetal fibronectin cultures or the clinical and legal implications of inappropriately managing preterm labor. Ultrasound s accuracy depends greatly on the skill of the person performing the examination and the quality of the images, not to mention the size of the patient and the fetal position. These technical and training issues have been addressed by the American Institute for Ultrasound in Medicine (AIUM), which has set the professional standards for minimal training requirements and equipment specifications. ACOG has also published specific guidelines that address training, quality assurance, safety, and clinical recommendations. Ultrasound s accuracy of detecting fetal anomalies remains controversial, with higher detection rates reported at tertiary centers and higher sensitivity rates overall for central nervous system and urinary tract verses cardiac anomalies. The safety of ultrasound has also come into question, and these concerns have been addressed by the AIUM. Ultrasound energy generates sound waves in a pulsed fashion that can theoretically raise the temperature of body tissues. This vibration effect, commonly referred to as cavitation, has been cited in some studies as potentially causing harm to developing fetuses. There have been no studies to demonstrate any adverse bioeffects on human fetuses as a result of exposure to low levels of ultrasound energy in use today. There remains a remote possibility

3 PRACTICE GUIDELINE Page 3 of 7 that adverse effects could be identified in the future; however, current evidence indicates that the potential benefits of ultrasound far outweigh these risks. ACOG and AIUM have issued position statements discouraging the nonmedical use of ultrasound for the purpose of gender identification or keepsake videos and pictures. This position is supported by the US Food and Drug Administration, which considers the nonmedical use of ultrasound to be an unapproved use of a medical device. The midwifery model of care is predominantly a noninterventive approach; therefore, a single ultrasound prior to 24 weeks may in fact reduce the likelihood of unnecessary interventions. In spite of the reliability and accuracy of ultrasound, its routine use in all pregnancies is still not recommended. Instead, menstrual dating remains the primary method for pregnancy dating in the absence of any complications. The Simple Solution: Rule of Eights In today s ultrasound-savvy environment, ultrasound biometery performed by an experienced provider has a fairly consistent 8% margin of error at any gestation. Therefore, one can potentially calculate and compare this margin of error against a dating discrepancy at any point in pregnancy. However, because ACOG has established guidelines for managing dating discrepancies up to 20 weeks gestation, using the 8% margin of error may be more useful in later gestations when there is discordance between menstrual and ultrasound dating. CALCULATING THE RULE OF EIGHTS 1. Double-check and recalculate the LMP due date (ideally with a computer) 2. Calculate the number of days difference between the LMP and US due dates 3. Convert the GA from the earliest US to days 4. Multiply this number by 0.08 for the 8% MOE 5. If the difference is greater, use the ultrasound date 6. If the MOE is greater, use the LMP date 7. Document the calculation in the chart with the final EDD EXAMPLE LMP 4/18/08 -> EDD 1/23/09 US 8/15/ wks -> US EDD 1/10/09 (13- day difference) GA of 20 wks 2 days = 142 days (20x7+2) 142 days x 0.08 = MOE Difference > MOE = US date Difference < MOE = LMP date Final EDD 1/10/09 Ultrasound in the First Trimester of Pregnancy In the first trimester, if a gestational sac is seen, its location should be documented. The gestational sac should be evaluated for the presence or absence of a yolk sac or embryo, and the crown-rump length is a more accurate indicator of gestational (menstrual) age than is mean gestational sac diameter. However, the gestational sac diameter may be recorded when an embryo is not identified. Caution should be used in presumptively diagnosing a gestational sac in the absence of a definite embryo or yolk sac. Without these findings, intrauterine fluid collection could represent a pseudogestational sac associated with an ectopic pregnancy. With transvaginal scans, cardiac motion should be observed when the embryo is 5 mm or greater in length. An embryo should be visible by transvaginal ultrasonography with a mean gestational sac diameter of 20 mm or greater. Fetal number should be reported, and amnionicity and chorionicity should be documented for all multiple gestations. The uterus and adnexal structures should be evaluated. The presence, location and size of adnexal masses should be recorded. The presence of leiomyomas should be recorded, and measurements of the largest or any potentially clinically significant leiomyomas may be recorded. The cul-de-sac should be evaluated for the presence or absence of fluid. For clients who desire an assessment of their individual risk of fetal aneuploidy, a standardized measurement of the nuchal translucency during a specific age interval is necessary. Nuchal translucency measurements should be used (in conjunction with serum biochemistry) to determine the risk of Down syndrome, trisomy 13, trisomy 18, or other anatomic abnormalities, such as heart defects. Ultrasound in the Second Trimester of Pregnancy Fetal cardiac activity, fetal number and fetal presentation should be reported. Any abnormal heart rates or rhythms should be reported. Multiple gestations require the documentation of additional information: chorionicity,

4 PRACTICE GUIDELINE Page 4 of 7 amnionicity, comparison of fetal sizes, estimation of amniotic fluid volume on each side of the membrane, and fetal genitalia. An estimate of amniotic fluid volume should be reported. The placental location, appearance, and relationship to the internal cervical os should be recorded. If a low-lying placenta or placenta previa is suspected early in gestation, verification in the third trimester by repeat ultrasonography is indicated. Transvaginal or transperineal ultrasonography may be considered if the cervix appears shortened. First-trimester crown-rump measurement is the most accurate means for ultrasound dating of pregnancy. Beyond this point, a variety of ultrasound parameters, such as biparietal diameter, abdominal circumference, and femoral diaphysis length, can be used to estimate gestational age. However, the variability of gestational age estimations increases with advancing pregnancy. Significant discrepancies between gestational age and fetal measurements may suggest the possibility of a fetal growth abnormality, intrauterine growth restriction, or macrosomia. The pregnancy should not be redated after a date has been calculated from an accurate earlier scan that is available for comparison. Currently, even the best fetal weight prediction methods can yield errors as high as plus or minus 15%. Three-Dimensional Ultrasonography The technical advantages of three-dimensional ultrasonography include its ability to acquire and manipulate an infinite number of planes and to display ultrasound planes traditionally inaccessible by two-dimensional ultrasonography. Despite these technical advantages, proof of a clinical advantage of three-dimensional ultrasonography in prenatal diagnosis in general is still lacking. Potential areas of promise include fetal facial anomalies, neural tube defects, and skeletal malformations where three-dimensional ultrasonography may be helpful in diagnosis as an adjunct to, but not a replacement for, two-dimensional ultrasonography. Ultrasound Facility Accreditation The American Institute of Ultrasound in Medicine and the American College of Radiology offer ultrasound facility accreditation. This process involves review of submitted ultrasound case studies, equipment use and maintenance, report generation, storage of images, and ultrasonographer and physician qualifications. Practices, not individuals, may be accredited in ultrasonography for obstetrics, gynecology, or both. Practices that receive ultrasound accreditation have been shown to improve compliance with published standards and guidelines for the performance of obstetric ultrasound examinations. Physicians who perform, evaluate, and interpret diagnostic obstetric ultrasound examinations should be licensed medical practitioners with an understanding of the indications for such imaging studies, the expected content of a complete obstetric ultrasound examination, and a familiarity with the limitations of ultrasound imaging. They should be familiar with the anatomy, physiology, and pathophysiology of the pelvis, the pregnant uterus, and the fetus. These physicians should have undergone specific training in obstetric ultrasonography either during or since their residency training and should be able to document this training. Completion of an approved residency in obstetrics and gynecology with documentation of obstetric ultrasound experience and training with certification by the American Board of Obstetrics and Gynecology is evidence of the necessary and appropriate training. Physicians are responsible for the quality and accuracy of ultrasound examinations performed in their names, regardless of whether they personally produced the images. Physicians also are responsible for the quality of the documentation of examinations and the quality control and safety of the environments and the procedures. Patient Safety Ultrasonography is safe for the fetus when used appropriately and when medical information about a pregnancy is needed; however, ultrasound energy delivered to the fetus cannot be assumed to be completely innocuous, and the possibility exists that such biological effects may be identified in the future. Ultrasonography should be performed only when there is a valid medical indication, and the lowest possible ultrasound exposure setting should be used to gain the necessary diagnostic information under the as-low-as-reasonably achievable principle. Diagnostic levels of

5 PRACTICE GUIDELINE Page 5 of 7 ultrasonography can produce physical effects, such as mechanical vibrations (referred to as cavitation) or an increase in tissue temperature under laboratory conditions. Although there is no reliable evidence of physical harm to human fetuses from diagnostic ultrasound imaging using current technology, public health experts, clinicians, and industry representatives agree that casual use of ultrasonography, especially during pregnancy, should be avoided. The use of either two-dimensional or threedimensional ultrasonography only to view the fetus, obtain a picture of the fetus, or determine the fetal sex without a medical indication is inappropriate and contrary to responsible medical practice. Viewed in this light, exposing the fetus to ultrasonography with no anticipation of medical benefit is not justified. The U.S. Food and Drug Administration views the promotion, sale, or lease of ultrasound equipment for making keepsake fetal videos as an unapproved use of a medical device. Use of ultrasonography without a licensed provider s order may be a violation of state or local laws or regulations regarding the use of a prescription medical device. Thus, ultrasonography should be used in a prudent manner to provide medical benefit to the patient. What gestational age represents the optimal time for an obstetrical ultrasound examination? In the absence of specific indications, ultrasound examination between weeks of gestation allows for a reasonable survey of fetal anatomy and an accurate estimation of gestational age. At weeks of gestation, anatomically complex organs, such as the fetal heart and brain, can be imaged with sufficient clarity to allow detection of many major malformations at a time when termination of pregnancy may still be an option. Therefore, the optimal timing for a single ultrasound examination in the absence of specific indications for a first-trimester examination is at weeks of gestation. Should routine measurement of cervical length be included in ultrasonography? The value of routine cervical length measurement in low-risk pregnancies has not been established; therefore, this practice currently is not recommended. Although there is an association between short cervix and preterm delivery, there are no data to support routine screening for all women. For certain pregnant women at high risk, serial evaluation of the cervical length may identify those at increased risk of primary or recurrent preterm birth. How and when is ultrasonography used to adjust gestational age? In general, ultrasound-established dates should take preference over menstrual dates when the discrepancy is greater than 7 days in the first trimester and greater than 10 days in the second trimester. Ultrasonography may be considered to confirm menstrual dates if there is a gestational age agreement within 1 week by crown-rump measurements obtained in the first trimester or within 10 days by an average of multiple fetal biometric measurements obtained in the second trimester (up to 20 weeks of gestation). Reassigning gestational age in the third trimester should be done with caution because the accuracy of ultrasonography is within 3-4 weeks. Before six weeks of gestation, dating can be done by measurement of the gestational sac, which is visible as early as 4 weeks of gestation and certainly by the fifth week of gestation. The head circumference is the most predictive parameter of gestational age between weeks of gestation because it predicts gestational age by 3.4 days. Combining various parameters improves the prediction of gestational age slightly over the use of head circumference measurement alone. In the third trimester, the best single measurement of gestational age based on fetal biometry is the femur length. However, reported accuracy of femur length ranges from 1 week in the second trimester to 3-4 weeks at term. How is the amniotic fluid volume evaluated using ultrasonography? The AFI technique is based on the division of the uterus into four quadrants and measuring the deepest vertical pocket of fluid in each quadrant and then adding the four measurements together. Oligohydramnios is described in

6 PRACTICE GUIDELINE Page 6 of 7 various ways. Two acceptable definitions are an AFI less than 5 cm or a maximum deepest vertical pocket of less than 2 cm. In a randomized clinical trial, the use of amniotic fluid index compared with single deepest pocket technique during antepartum surveillance was associated with significantly higher rates of suspected oligohydramnios, which led to increased interventions without a demonstrable benefit. Recent studies suggest that AFI is a weaker predictor of perinatal outcome than has been classically suggested. Hydramnios commonly is described by an AFI greater than or equal to 24 cm or a maximum deepest vertical pocket of equal to or greater than 8 cm. How may ultrasonography be used to detect fetal chromosome abnormalities in the second trimester? With the current limitations of ultrasonography, ultrasound evaluation is not recommended as a primary screening modality for Down syndrome and other chromosomal abnormalities. At this time, risk adjustment based on secondtrimester ultrasound markers should be limited to individuals with expertise in the area. How is ultrasonography used to detect disturbances in fetal growth? Four standard fetal measurements generally are obtained as part of any complete obstetric ultrasound examination after the first trimester: fetal abdominal circumference, head circumference, biparietal diameter, and femur length. Fetal morphologic parameters can be converted to fetal weight estimates using published formulas and tables. Contemporary ultrasound equipment calculates and displays an estimate of fetal weight on the basis of these formulas. If the estimated fetal weight is below the 10 th percentile, further evaluation should be considered for intrauterine growth restriction. Similarly, if the estimated fetal weight is more than 4,000 grams or 4,500 grams, evaluation should be considered for fetal macrosomia. Serial ultrasound measurements are of considerable clinical value in confirming or excluding the diagnosis and assessing the progression and severity of growth disturbances. Serial ultrasonography to determine the rate of growth should be obtained approximately every 2-4 weeks. Measurements at shorter intervals (less than 2 weeks) may overlap and cause interpretation errors. PROCEDURE FOR DATING: 1. Careful inquiry of every woman s LNMP recall and bleeding history must be taken into consideration and first-trimester ultrasound obtained if there is any question about the accuracy of this information. 2. Gestational age permitting, first-trimester ultrasound should be used to establish the gestational age and EDD if there is any uncertainty regarding the EDD due to: a pelvic examination discrepancy (> +/- two weeks), an unknown or uncertain last menstrual period (LMP), or irregular menstrual cycles. 3. Various information and methods for dating a pregnancy may be available for consideration. EDD should be based on the most accurate information/method available for the individual pregnancy. Dating accuracy is prioritized in this order: a. In vitro fertilization (+/- 1 day); b. Ovulation induction, artificial insemination, a single intercourse record, ovulation predictor assay or basal body temperature measurement (+/- 3 days); c. First-trimester sonographic assessment (6-11 weeks) (+/- 8%); d. Reported LMP, if reliable; e. Twelve to 22-week second-trimester sonographic examination (CRL or BPD, HC, AC and FL) if the LMP is unknown or uncertain or if the LMP is more than 8 percent discordant from the sonographic examination; f. Twenty-three to 28-week second-trimester sonographic examination (BPD, HC, AC, FL) confirmed by a second examination 3-6 weeks later demonstrating normal interval growth (+/- 8%); and then g. Third-trimester sonographic evaluation (+/-8%). 4. The nurse-midwife will calculate and document in the client s chart (health history and face sheet) how the EDD was established.

7 5. Current ACOG guidelines recommend changing the EDD when a first-trimester ultrasound differs more than 7 days from the LMP date or more than 10 days between 12 and 20 weeks gestation. (Interestingly, the rule of eights would represent + 5 days difference and days difference at 20 weeks gestation.) 6. When a first-trimester dating ultrasound has not been previously performed a dating ultrasound at 16 to 22 weeks should be obtained. This examination can be combined with a basic screening anatomy ultrasound. 7. Situations with abnormal fetal biometric ratios (e.g., head / abdominal circumference [HC/AC], biparietal diameter /femur length [BPD/FL]) limit the accuracy of biometric measurements for pregnancy dating and may signal fetal anomalies or karyotype abnormalities. Such circumstances require individualized assessment by an advanced prenatal care provider to establish dating and recommend ongoing assessment (s) and management. 8. Once a final EDD has been established, it should remain the set point clinical marker for all obstetric decision making and any future assessments of adequate fetal growth. 9. When clinical decisions late in pregnancy necessitate gestational age information and the dates have not been established prior to the 29th week, fetal maturity may be assumed when one of the following criteria are met: a. 20 weeks of audible fetal heart tones by a non-electronic method b. 30 weeks of audible fetal heart tones by an electronic method c. 36 weeks from a positive pregnancy test in a reliable laboratory. 10. If a significant difference between a late second- or early third-trimester ultrasound EDD and the reported LMP due date exists or an y other dating discordance between menstrual and ultrasound dating after twenty weeks of gestation exists, the Nurse Midwife is encouraged to utilize the Rule of Eights in effort to obtain the most accurate gestational dating. 11. The nurse-midwife is encouraged to discuss with each client the limitations of ultrasound technology. ATTACHMENTS: Rule of Eights computer formula REFERENCES: ACOG Practice Bulletin, No 101. (2009). Ultrasonography in pregnancy. Obstetrics & Gynecology, 113(2), Hunter, L.A. (2009). Issues in pregnancy dating: revisiting the evidence. Journal of Midwifery and Women s Health, 54(3), Originated: July, 2010 BELIEVE MIDWIFERY SERVICES PRACTICE GUIDELINE Page 7 of 7 Penny Lane MSN, CNM DATE: 11/11/2013 Holly Hopkins MSN, CNM DATE: 8/23/2011 Michelle Burton DATE: 6/4/2012