ISUOG Practice Guidelines (updated): performance of 11–14‐week ultrasound scan

The International Society of Ultrasound in Obstetrics and Gynecology (ISUOG) is a scientific organization that encourages sound clinical practice and high-quality teaching and research related to diagnostic imaging in women's healthcare. The ISUOG Clinical Standards Committee (CSC) has a remit to develop Practice Guidelines and Consensus Statements as educational recommendations that provide healthcare practitioners with a consensus-based approach, from experts, for diagnostic imaging. They are intended to reflect what is considered by ISUOG to be the best practice at the time at which they are issued. Although ISUOG has made every effort to ensure that Guidelines are accurate when issued, neither the Society nor any of its employees or members accepts liability for the consequences of any inaccurate or misleading data, opinions or statements issued by the CSC. The ISUOG CSC documents are not intended to establish a legal standard of care, because interpretation of the evidence that underpins the Guidelines may be influenced by individual circumstances, local protocol and available resources. Approved Guidelines can be distributed freely with the permission of ISUOG ([email protected]). Performing a routine first-trimester ultrasound examination at 11 + 0 to 14 + 0 weeks' gestation is of value for confirming viability and plurality, accurate pregnancy dating, screening for aneuploidies, identification of major structural anomalies and screening for preterm pre-eclampsia. This document aims to provide guidance for healthcare practitioners performing, or planning to perform, pregnancy scans at 11 + 0 to 14 + 0 weeks. Details of the grades of recommendation and levels of evidence used in ISUOG Guidelines are given in Appendix 1. In general, the main goal of a pregnancy ultrasound scan is to provide accurate information which will facilitate delivery of optimized antenatal care, ensuring the best possible outcomes for mother and fetus. In early pregnancy, it is important to confirm viability, establish gestational age accurately, determine the number of fetuses and, in the presence of a multiple pregnancy, assess chorionicity and amnionicity. Towards the end of the first trimester, the scan also offers an opportunity to detect major fetal abnormalities and, in healthcare systems that offer first-trimester aneuploidy screening, to measure the nuchal translucency (NT) thickness. However, many major malformations may develop later in pregnancy or may not be detected even with appropriate equipment and in the most experienced of hands. If an earlier first-trimester ultrasound scan has not been done, it is advisable to offer the first scan when gestational age is estimated to be between 11 + 0 and 14 + 0 weeks' gestation, as this provides an opportunity to achieve the aforementioned aims, i.e. confirm viability, establish gestational age accurately, determine the number of viable fetuses and, if requested, evaluate fetal anatomy and risk of aneuploidy1-18. Before starting the examination, a healthcare provider should counsel the woman/couple regarding the potential benefits and limitations of the first-trimester ultrasound scan (GOOD PRACTICE POINT). Individuals who perform obstetric scans routinely should have specialized training that is appropriate to the practice of diagnostic ultrasound for pregnant women (GOOD PRACTICE POINT). An examination report should be produced as an electronic and/or paper document (see Appendices 2 and 3 for examples). The document should be stored locally and, in accordance with local protocol, made available to the woman and referring healthcare provider (GOOD PRACTICE POINT). There are no indications that the use of B-mode or M-mode prenatal ultrasonography may be harmful during the first trimester, due to their limited acoustic output20, 21. However, scanning time should be limited and the lowest possible power output should be used to obtain diagnostic information according to the ALARA (As Low As Reasonably Achievable) principle (GOOD PRACTICE POINT). Doppler ultrasound is, however, associated with greater energy output and, therefore, there are more potential bioeffects, especially when it is applied to a small region of interest and in the embryonic period before 11 weeks' gestation20, 22, 23. From 11 + 0 to 14 + 0 weeks, spectral Doppler, color flow imaging, power Doppler imaging and other Doppler ultrasound modalities may be used routinely for certain clinical indications, such as screening for aneuploidies and cardiac anomalies. When performing Doppler ultrasound, the displayed thermal index (TI) should be ≤ 1.0 and the exposure time should be kept as short as possible (usually no longer than 5–10 min). Scanning of the maternal uterine arteries (UtA) at any point in the first trimester is unlikely to have any fetal safety implications as long as the embryo/fetus lies outside the Doppler ultrasound beam22. These Guidelines represent an international benchmark for the first-trimester ultrasound scan, but consideration must be given to local circumstances, protocols and medical practice. If the examination cannot be completed in accordance with these Guidelines, it is advisable to document the reasons for this. In most circumstances, it will be appropriate to repeat the scan, or to refer the case to another healthcare practitioner. This should be done as soon as possible, to minimize unnecessary patient anxiety and any associated delay in achieving the desired goals of the initial examination (GOOD PRACTICE POINT). Determination of chorionicity and amnionicity is important for care, testing and management of multifetal pregnancies. Chorionicity should be determined in early pregnancy, when characterization is most reliable24, 25. Once this is accomplished, further antenatal care, including the timing and frequency of ultrasound examinations, should be planned according to the available health resources and ISUOG or local guidelines26 (GOOD PRACTICE POINT). In early pregnancy, viability is defined by identification of a fetal heartbeat, which is achieved most easily using ultrasound. Fetal cardiac activity can be identified with 2D B-mode ultrasound and the heartbeat can be heard using spectral Doppler. The heart rate, which should be recorded, can be measured using either M-mode or spectral Doppler and is best assessed over a number of cycles (GOOD PRACTICE POINT). Cardiac activity is typically visible from 5–6 weeks' gestation. Heart rate increases with gestational age up to 10 weeks' gestation (mean, 171 bpm) and then decreases through to 14 + 0 weeks' gestation (mean, 156 bpm)27. Fetal tachy- or bradycardia may be indicative of aneuploidy or associated with a structural cardiac abnormality28, 29. If the fetal heart rate lies outside the normal range, it should be reassessed later in the examination. Once viability has been demonstrated, it is important to confirm the intrauterine nature of the pregnancy. An intrauterine gestational sac should be bounded completely by myometrium. This is best assessed by performing a sweep covering the entire uterus (GOOD PRACTICE POINT). The integrity of the uterus may be breached when a pregnancy is located in a Cesarean section scar (see section on ‘Assessment of risk of obstetric complications’) or associated with a rudimentary uterine horn. There are specific charts for assessing first-trimester fetal biometry38. Systematic measurement of cephalic, abdominal and femoral biometry enables documentation of the presence of essential anatomical landmarks, and abnormalities in measurements can reveal early expression of serious pathologies. However, the cut-off values to be used and the follow-up procedures must be decided in accordance with local protocols, in order to avoid an excessive number of false-positive findings or follow-up examinations. Crown–rump length (CRL) should be measured as part of the routine first-trimester scan, either transabdominally or transvaginally (Figure 1a). This measurement should be performed, following standard criteria, with the fetus oriented horizontally on the screen so that the measurement line between crown and rump is at about 90° to the ultrasound beam. The fetus should be in a neutral position (i.e. neither flexed nor hyperextended). The image should be magnified to fill most of the width of the ultrasound screen. Calipers should be placed on the end points of the crown and the rump, which need to be visualized clearly30, 31. The measurement of CRL should be used to estimate gestational age in all cases except in pregnancies conceived by in-vitro fertilization32, 33. When multiple CRL measurements have been taken, gestational age should be assessed based on the best-quality CRL measurement between 45 and 84 mm. A number of different charts have been published and there are small but significant variations in reported measurements for gestational age34. Although older charts are still used widely, it is recommended to use recent, international, prescriptive charts35, because these take into account improvements in image and machine quality and aim to avoid possible statistical bias36, 37. The CRL (and not the calculated gestational age) should be used as a gestational reference to define where measurements of NT, UtA Doppler pulsatility index (PI) and biochemical markers free β-human chorionic gonadotropin (β-hCG), pregnancy-associated plasma protein-A (PAPP-A) and placental growth factor (PlGF) lie in relation to the normal range. The CRL is reduced in fetuses affected by and and should be not to findings by in fetuses that have structural anomalies. should be if the CRL is than based on an earlier ultrasound and are measured in the of the fetal (Figure for measurement of have been or to the should be made in accordance with the used to establish the measurements for and/or abdominal or abdominal may be in early screening for and is measured in an section of the fetal at the in which the is visualized (Figure at the of the is either measured with or calculated from the abdominal and measure the are placed on the of the from the covering the to the abdominal measure the are placed on the of the the at the may be calculated using the + + An of performing this measurement is that the image used to it also the in length is measured in the of the (Figure The are placed at either end of the which is An of performing this measurement is that it that the the of the which may reveal early the presence of early of fetal structural anomalies is also on the standard of equipment available for screening, the of the and and the of the anomalies in the of structural have been and it is not these markers perform in levels of screening, a of for a structural at 11 + 0 to 14 + 0 weeks' gestation and a more of for examination of the fetus in the first trimester There is limited evidence the health of early identification of fetal structural of of of no by in their of and nuchal translucency of heart at of Heart with visible abdominal or visible and not Crown–rump length and nuchal translucency of of no by in their with of translucency translucency in of the Heart activity with heart heart position with cardiac to of with on and color Doppler in on or color Doppler on or color Doppler of on Doppler normal position in in with arteries presence with and free with and free and in relation to and to uterine Cesarean section scar into and The 11 + 0 to 14 + scan provides an opportunity to assess fetal anatomy and should not be limited to of fetal CRL and provides a of screening for aneuploidies, this cannot structural which may be associated with a more of of a structural may an than a to testing for structural anomalies can be detected in all and their presence or should be assessed as a standard in all for an 11 + 0 to 14 + scan (GOOD PRACTICE POINT). structural anomalies in pregnancies as at by to of structural anomalies on routine examination of the than examination of risk of normal anatomy at 11 + 0 to 14 + 0 provides early for most pregnant identification of a major earlier and more time for and of fetal anatomy at 11 + 0 to 14 + 0 is best achieved using and and may be to a examination of fetal and time to be for this a examination is not it may provide image for the of fetal especially in women with uterine and/or this time the fetus in of many anatomical by ultrasound is best achieved at weeks' gestation (GOOD PRACTICE POINT). have that the of a examination including a protocol is associated with a significant in the rate of anomalies in early As and more in screening at 11 + 0 to 14 + 0 weeks, from a protocol based on to a more will of a and a of structural anomalies. A to of the fetal anatomy at 11 + 0 to 14 + 0 should the following of and An of the fetus should be assessed (Figure The should as with small or or (Figure The presence or of a should be of the placental in relation to the can be in the first trimester and to false-positive of However, in a patient with a of a Cesarean a of the in the early of an This is in the section on ‘Assessment of risk of obstetric the the presence or of and should be and A in is in early gestation, in the scan, this cannot be used as a for anomalies. The are visualized as a sac the fetus and not with the When there is a of a is identified in the In multiple pregnancy, chorionicity and amnionicity should be determined and (Figure and of the fetal and is best achieved using a of and The is used to of the and the of the should be visible by 11 completed gestational weeks. 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routine screening for preterm by maternal and in all measurements of and for a of the on the of the risk from screening by maternal and (GOOD PRACTICE POINT). first-trimester screening for preterm women identified as at risk should between 11 and + weeks' gestation at a of to be every either weeks' gestation, when delivery or when is should not be to all pregnant In women with either or may the of preterm and These Guidelines should be Society of Ultrasound in Obstetrics and ISUOG Practice Guidelines of ultrasound Ultrasound or as and to the or a of or a of evidence of as + to the and of of evidence including as 2 to the and of or evidence from as or + is not to this as no or in this and of and The is not for the or of any information by the than should be to the for the