TECHNICAL CHALLENGES IN SONOGRAPHY OF GRAVID OBESE WOMEN: PITFALLS AND SOLUTIONS

Author: Avni KP Skandhan, Aster MIMS,  Kottakkal, Kerala. Email: avniskandhan@gmail.com

The World Health Organization (WHO) defines an individual as overweight (1) if their body mass index (BMI) is ≥ to 25 Kg/m2. An individual with a BMI ≥ 30 Kg/m2 is defined as obese.(1) 

The American College of Obstetricians and Gynaecologists (ACOG) describes three levels of obesity that reflect the increasing health risks that go along with increasing BMI, with the lowest risk being a BMI of 30 – 34.9 Kg/m2, medium risk is a BMI of 35.0–39.9 Kg/m2 and the highest risk is a BMI of 40 Kg/m2 or greater.(2) The same categories of obesity are classified as Classes I, II and III respectively by the National Institute for Health and Clinical Excellence.(3).

The worldwide prevalence of obesity nearly tripled between 1975 and 2016; with over 1.9 billion adults who are obese (1), thus transforming obesity from a clinical concern to a socio-clinical concern. The effects of obesity on pregnancy may extend from the prenatal to the perinatal period and have long-term consequences for the foetus. Several studies have reported an increased risk of complications like miscarriage, stillbirth, pre-eclampsia, gestational diabetes and thromboembolic disorders in obese gravid women.(4-14) Obese gravid women also have a  higher incidence of caesarean section, anaesthetic problems, wound infections (15), and chances of developing hernia.  Obesity may also lead to an increase in birth difficulties, macrosomia and perinatal death.(4,5)  Congenital anomalies such as neural tube defect (NTD), orofacial clefts, anorectal atresia, omphalocele, diaphragmatic hernia and congenital heart defects are associated with maternal obesity.(6,7, 11-13, 16)

Sonography is an important modality for prenatal diagnosis and foetal management and interventions if there are associated foetal abnormalities.(8-10) Sonography is used to assess the foetal anatomy, screen for foetal anomalies and assess presence of foetal aneuploidies.(7, 17, 18) Foetal anatomy, foetal anomalies (19) and estimation of foetal weight (18) is poorly delineated in an obese gravida sonographically. Several studies have reported a suboptimal visualization of cardiac (14,20,21) and the cranial and spinal structures (5) in the obese mothers. The abdominal panniculus of the maternal abdomen limits the visualisation (8), due to hampered ultrasound insonation at a greater depth, an increase in the absorption of the ultrasound by the adipose layer and by increased back scatter from refraction leading to degradation of the image quality.(5, 17,18, 22, 24, 25) Several studies have explored the relationship between ultrasound image visibility and the different BMI groups.(5, 6, 10-16) These studies largely showed a decreasing ability to scan foetuses of obese women as the obesity category increased. Thornburg et al reported a visibility of 72% in Class I patients (BMI: 30-34.9 Kg/m2 )  a  visibility of 61% in  Class II (BMI : 35 – 39.9 Kg/m2) and a visibility of 49% in class III ( BMI ≥ 40 Kg/m2 ).(26) A similar study conducted by Dashe et al reported values corresponding to 57%, 41% and 30% respectively. Fuchs et al suggests that even if women with Class I obesity have no abdominal folds, the chances of them having a tense hard abdomen leads to a difficulty for ultrasound penetration.(28) Conversely, women with a Class III obesity have abdominal folds, yet it may be possible to scan through a small abdominal ‘‘window’’.(28) Sonography in obese mothers may result in inability to view structures and necessitate a repeat examination to the extent mothers may need to be called for repeated scans and yet there is a suboptimal visualisation.(5) 

The scans demand additional physical stress, on the person doing the sonography during examinations because of the various technical challenges that are encountered due to additional allocation of time and pressure in the scan period.(5) At times the people carrying out sonography end up acquiring muscular injuries as a result of performing such scanning methodologies.(29-31) The stress exists not only for the person performing the sonography but also in the obese mothers who end up having multiple scans, leaving them apprehensive especially if they have an underlying family history of anomalies.(9) 

Various studies have been conducted to better understand how to improvise the visibility in the obese mothers to optimize foetal visualisation.(5, 6, 10-16) The primary goal in doing this is to minimise the distance between the sonography probe and the foetus, and to take maximal leverage of the various advanced ultrasound technologies available in the newer ultrasound machines for the post-processing (32).  

After a review of articles; the various modifications that can be attempted in such scenarios to improve visibility can be at the: 

1) Maternal end 

2) Ultrasound machine 

3) Technique

Maternal End:

• Optimal foetal position: Wait for the optimal foetal position with the foetal spine posterior which would aid in a better visualisation of the cardia.(33) 

• Maternal position: The mother lying in various alternate positions such as decubitus, oblique, semi-recumbent or upright will help the abdominal fat to fall away from the region of interest, aiding the thinned out abdominal wall to be used as a window while pointing the transducer towards the region of interest. 

• Mobilising abdominal fat :  Some maternal abdomens are significantly floppy, but this can be used maximally by making the patient herself lift up the fatty part of the abdomen or asking an assistant to do the same and thereby using the crease inferior to it as a region of minimal distance between the foetus and the ultrasound probe.(8, 22)

• Multiple maternal positions: Positioning of the mother can be changed based on the foetal position in relation to the maternal abdomen over the scan period to visualise the anatomy of the various regions.(32) 

• Full urinary bladder: If the visualisation is difficult, making the patient fill the bladder displaces the uterus cephalad where the anterior abdominal fat is thinner; thereby improving visibility.(34)

Ultrasound machine end:

• Usual obstetric scans are done with a 2-5 MHz probe. If this can be replaced by a lower frequency transducer (e.g. 1MHz), it will lead to less absorption, less attenuation and more penetration; however, there is a degradation of the resolution noted. 

• Penetration pre-set: Most of the newer machines come with a pre-set of penetration enabled which uses certain programs that correct and adjust for the speed changes that occur in fatty tissue. It leads to an improved resolution and a greater depth of penetration. 

• Trans-vaginal scan:  A transvaginal approach is a method of choice in the first trimester and in the scenarios where the foetal parts that are placed close to the cervix are sub optimally visualised e.g. intracranial anatomy in a cephalic foetus. 

• Vaginal probe: Vaginal probe alternate to the trans-vaginal scan, can also be placed directly in the umbilicus, where an acoustic window can be provided with adequate ultrasound gel application. This methodology has been shown to helpful for foetal cardiac examinations in obese maternal abdomens.(35)

• Tissue harmonic imaging: A technique that helps improve the contrast resolution of a grey scale image especially in patients who are difficult to image with conventional techniques.(33) 

• Compound imaging: Multiple slices of the images are obtained from different angles and are used to generate an improved composite sonographic image.(33)

• Speckle reduction filters: This is a post‐processing tool that improves image quality and contrast and leads to better edge recognition.

Technique End:

1. Site of probe placement: The primary goal in an ultrasound is to get the organ of interest as close as possible to the transducer to improve visibility. The thickest portion of the abdominal fat is located in the midline between the umbilicus and the pubic symphysis. Placing the probe away from this region and yet visualising the foetus would improve visibility.(8)  
2. Foetal mobilisation:  As the pregnancy advances, to certain extent it is possible to mobilise the foetus – in the second and third trimesters and same could be attempted using a free hand and without an undue pressure on the foetus.(32)

Ergonomic tips for the ultrasound performer: 

Scanning an obese patient leads to multiple repetitive injuries due to applying pressure for long periods of time, improper position and longer scanning periods. Knowing appropriate posture and avoiding awkward and jerky twisting movements or undue period of pressures should be avoided to prevent any injury. (8)

MRI – A Future problem-solving tool:

MRI might be a problem-solving tool in the future for obese gravidae in whom repeated ultrasound and different manoeuvres are inconclusive. Several studies have found there is no alteration of the foetal heart rate, or any effect on the intrauterine foetal growth after a MRI study.(37-40). There is considerable speculation regarding the affect of acoustic noise on the foetuses, and studies have provided reassuring results with no significant risk to the foetus during perinatal MRI.(41,42) Foetal MRI is routinely being used to better delineate the foetal anatomy in cases suspected with anomalies sonographically (43-49). Though MRI is not routinely used for evaluation of the foetuses in obese gravida, this is a possibility that needs to be studied further, because quality of MRI images is less affected by obesity than ultrasound images.(8) 

Conclusion 

Obesity is a growing epidemic.  Obese patients have an increased risk of adverse outcomes in the mothers and the foetuses. However, the pregnant obese patients present a significant technical challenge for performing sonography. Keeping in mind the patient habitus, foetal position, maternal anatomy and machine settings and options, the performer should leverage the maximal changes to optimise the quality of the images, without significant muscular strain of the performer. Similarly, the maternal anxiety can be alleviated by proper counselling and patient interaction during the scan. 

References: 

1. https://www.who.int/news-room/fact-sheets/detail/obesity-and-overweight
2. https://www.acog.org/patient-resources/faqs/pregnancy/obesity-and-pregnancy
3. National Institute for Health and Clinical Excellence. Obesity: the prevention, identification, assessment and management of overweight and obesity in adults and children. National Institute for Health and Clinical Excellence (NICE), 2006; http://www.nice.org.uk/guidance/CG43 .
4. World Health Organization. Obesity and overweight Fact Sheet 2016; [Internet]. [cited 2017 May 7]. Available from: http://www.who.int/mediacentre/factsheets/fs311/en/.
5.  Maxwell C, Dunn E, Tomlinson G, Glanc P. How does maternal obesity affect the routine fetal anatomic ultrasound? J Matern Fetal Med 2010;23(10):1187–92. 
6. Stothard K, Tennan P, Bell R, Rankin J. Maternal Overweight and Obesity and the Risk of Congenital Anomalies: A Systematic Review and Meta-analysis. JAMA 2009;301(6): 636–50. 
7. Tsai PJ, Loichinger M, Zalud I. Obesity and the challenges of ultrasound fetal abnormality diagnosis. Best Practice and Research: Clin Obstet Gynecol 2015;29(3):320–7. 
8. Maxwell C, Glanc P. Imaging and Obesity: A Perspective During Pregnancy. AJR 2011;196(2):311–9. 
9. Tsai LJ, Ho MK, Pressman EL, Thornburg L. Ultrasound screening for fetal aneuploidy using soft markers in the overweight and obese gravida. Prenat Diagn 2010;30(9): 821–6. 
10. Khoury F, Ehrenberg H, Mercer B. The impact of maternal obesity on satisfactory detailed anatomic ultrasound image acquisition. J Matern Fetal Med 2009;22(4):337–41. 
11.  Agaard-Tillery KM, Flint Porter T, Malone FD, Nyberg DA, Collins J, Comstock CH, et al. Influence of maternal BMI on genetic sonography in the FaSTER trial. Prenat Diagn 2010;302010;14(1):22. 
12.  Racusin D, Stevens B, Campbell G, Aagaard K. Obesity and the Risk and Detection of Fetal Malformations. Semin Perinatol 2012;36(3):213–21. 
13. Hildebrand E, Gottvall T, Blomberg M. Maternal Obesity and Detection Rate of Fetal Structural Anomalies. Fetal Diagn Ther 2013;33(4):246–51. 
14. Hendler I, Blackwell SC, Bujold E, Treadwell MC, Wolfe HM, Sokol RJ, et al. The impact of maternal obesity on mid-trimester sonographic visualization of fetal cardiac and craniospinal structures. Int J Obes 2004;28(12):1607–11.
15. Hartge D, Spiegler J, Schroeer A, Deckwart V, Weichert J. Maternal super-obesity. Arch Gynecol Obstet 2016;293(5): 987–92
16. Dashe J, Mcintire D, Twickler D. Effect of Maternal Obesity on the Ultrasound Detection of Anomalous Fetuses. Obstet Gynecol 2009;113(5):1001–7.
17. Weichert J, Hartge D. Obstetrical Sonography in Obese Women: A Review. J Clin Ultrasound 2011;39(4):209–16
18.  O’brien CM, Poprzeczny A, Dodd J. Implications of maternal obesity on fetal growth and the role of ultrasound. Expert Rev Endocrinol Metab 2017;12(1):45–58.
19. Maxwell, C, Dunn, E, Tomlinson , G, Glanc, P. How does maternal obesity affect the routine fetal anatomic ultrasound? The Journal of Maternal-Fetal & Neonatal Medicine. 2010; 23(10): 1187-1192.
20. Thornburg L, Miles K, Ho M, Pressman E. Fetal anatomic evaluation in the overweight and obese gravida. Ultrasound Obstet Gynecol 2009;33(6):670–5. 
21.  Adekola H, Soto E, Dai J, Lam-Rachlin J, Gill N, Leon-Peters J, et al. Optimal visualization of the fetal four-chamber and outflow tract views with transabdominal ultrasound in the morbidly obese: Are we there yet? J Clin Ultrasound 2015;43(9):548–55.
22. Weichert J, Hartge D. Obstetrical Sonography in Obese Women: A Review. J Clin Ultrasound 2011;39(4):209–16.
23. Pasko D, Wood S, Jenkins S, Owen J, Harper L. Completion and Sensitivity of the Second-Trimester Fetal Anatomic Survey in Obese Gravidas. J Ultrasound Med 2016;35(11): 2449–57
24. Phatak M, Ramsay J. Impact of maternal obesity on procedure of mid-trimester anomaly scan. J Obstet Gynaecol 2010;30(5):447–50. 
25.  Best K, Tennant PWG, Bell R, Rankin J. Impact of maternal body mass index on the antenatal detec
26. Thornburg LL, Miles K, Ho M, Pressman EK. Fetal anatomic evaluation in the overweight and obese gravida. Ultrasound Obstet Gynecol 2009; 33: 670–675.
27. Dashe JS, McIntire DD, Twickler DM. Maternal obesity limits the ultrasound evaluation of fetal anatomy. J Ultrasound Med 2009; 28: 1025–1030.
28. Fuchs F, Houllier M, Voulgaropoulos A, Levaillant JM, Colmant C, Bouyer J, et al. Factors affecting feasibility and quality of second-trimester ultrasound scans in obese pregnant women. Ultrasound Obstet Gynecol 2013;41(1):40–6
29. Harrison G, Harris A. Work-related musculoskeletal disorders in ultrasound: Can you reduce risk? Ultrasound 2015;23(4): 224–30. 
30. Evans K, Roll S, Baker J. Work-Related Musculoskeletal Disorders (WRMSD) Among Registered Diagnostic Medical Sonographers and Vascular Technologists. J Diagn Med Sonography 2009;25(6):287–99. 
31. Pike I, Russo A, Berkowitz J, Baker V, Lessoway VA. The prevalence of musculoskeletal disorders among diagnostic medical sonographers. J Diagn Med Sonography 1997;13(5): 219–27.
32. Han, C, Holliman, K, Tomlinson , G, Glanc, P. How to optimize imaging in the obese gravida. MJH Life Sciences. [Online] 2019;64(06): . Available from: https://www.contemporaryobgyn.net/article/how-optimize-imaging-obese-gravida [Accessed 10/05/2020].
33. Oktar SO, Yucel C, Ozdemir H, Uluturk A, Isik S. Comparison of conventional sonography, real-time compound sonography, tissue harmonic sonography, and  tissue harmonic compound sonography of abdominal and pelvic lesions. Am J Roentg. Nov 2003;181(5):1341-1347.
34. Benacerraf B. The use of obstetrical ultrasound in the obese gravida. Sem Perinatol. 2013;37:345-347.
35. Rosenberg JC, Guzman ER, Vintzileos AM, Knuppel RA. Transumbilical placement of the vaginal probe in obese pregnant women. Obstet Gyncecol. 1995;85:132-134.
36. Paladini, D, Holliman, K, Tomlinson , G, Glanc, P. Sonography in obese and overweight pregnant women: clinical, medicolegal and technical issues. Ultrasound in Obstetrics and gynaecology. 2009;33(06): 720-729.
37. Myers C, Duncan KR, Gowland PA, Johnson IR, Barker PN. Failure to detect intrauterine growth restriction following in utero exposure to MRI. BrJ Radiol 1998;71:549–51. 
38. Poutamo J, Partanen K, Vanninen R, Vaino P, Kirkinen P. MRI does not change fetal cardiotocographic parameters. Prenat Diagn 1998;18:1149–54. 
39. Barker PN, Johnson IR, Harvey P, Gowland PA, Mansfield P. A three year follow-up of children imaged in utero with echo-planar magnetic resonance imaging. Am J Obstet Gynecol 1994;170:32–33. 
40. Clements H, Duncan KR, Fielding K, Gowland PA, Johnson IR, Barker PN. Infants exposed to MRI in utero have a normal paediatric assessment at 9 months of age. BrJ Radiol 2000;73:190–4.
41. Baker PN, Johnson IR, Harvey PR, Gowland PA, Mansfield P. A three-year follow-up of children imaged in utero with echo-planar magnetic resonance. Am J Obstet Gynecol 1994;170:32–3. 
42. Gover P, Hykin J, Gowland P, Wright J, Johnson I, Mansfield P. An assessment of the intrauterine sound intensity level during obstetric echo-planar magnetic resonance imaging. BrJ Radiol 1995;68:1090–4. doi:10.1259/0007-1285-68-814-1090
43. Plunk M.R., Chapman T. The Fundamentals of Fetal MR Imaging: Part 1. Curr. Prob. Diagn. Radiol. 2014;43:331–346. doi: 10.1067/j.cpradiol.2014.05.014.
44. Manganaro L., Bernardo S., Antonelli A., Vinci V., Saldari M., Catalano C. Fetal MRI of the central nervous system: State-of-the-art. Eur. J. Radiol. 2017;93:273–283. 
45. Glenn O.A. MR imaging of the fetal brain. Pediat Radiol. 2010; 40:68–81. doi: 10.1007/s00247-009-1459-3.
46. Huisman T.A., Kellenberger C.J. MR imaging characteristics of the normal fetal gastrointestinal tract and abdomen. Eur. J. Radiol. 2008;65:170–181. doi: 10.1016/j.ejrad.2007.02.013.
47. Furey E.A., Bailey A.A., Twickler D.M. Fetal MR Imaging of Gastrointestinal Abnormalities. RadioGraphics. 2016;36:904–917. doi: 10.1148/rg.2016150109.
48. Rodríguez M.R., Ten P.M., Pedregosa J.P., López C.B., Degenhardt I.T., Abascal I.P. Fetal MRI: Thoracic, abdominal and pelvic pathology. EPOS. 2012;76:9–28.
49. Mehollin-Ray A.R., Cassady C.I., Cass D.L., Olutoye O.O. Fetal MR Imaging of Congenital Diaphragmatic hernia. RadioGraphics 2012; 32:1067–1084. doi: 10.1148/rg.324115155.