1. The Impact of Maternal Obesity on Obstetric Ultrasound Accuracy
Dr Sawsan Al-Obaidly Consultant, Maternal-Fetal Medicine Women’s Hospital, Hamad Medical Corporation,
Doha-Qatar

2. DISCLOSURE
I do not have any relevant financial relationship with commercial interest to disclose.

3. Objectives
The impact of maternal obesity on fetal weight estimation accuracy
How to scan a heavy woman
Macrosomia
The impact of maternal obesity on fetal morphology scan
Ultrasound ergonomics and safety consideration

4. Multiple Abdominal Surgeries
Obesity
Multiple Abdominal Surgeries
Multiple Pregnancy
COFACTORS IMPAIRING THE ACOUSTIC WINDOW:

5. FMU-September 2016 Variable Non-Obese BMI<30 Obese BMI≥30 p value
Total= 603
Variable
Non-Obese BMI<30
Obese BMI≥30
p value
Total
279
324
BMI
25.5±3
35.7±5 DM
30(11%)
57(18%)
0.017
IVF
16(6%)
49(15%)
0.0003
Singleton
239(85%)
232(72%)
0.0001
Twins
34(12%)
80(24%)
Triplets
9(3%)
12(4%)

6. Maternal Obesity and Fetal Ultrasound
Abdominal obesity limits the technical quality of the ultrasound examination.
Maternal obesity can significantly reduce the accuracy of sonographic fetal weight estimation.
Reddy, U. M., et al. Obstet Gynecol,2014
Aksoy, H et al. J Obstet Gynaecol Res 2015

7. Non-anomalous, Singleton, cephalic GA 36 – 42 weeks
Prospective study
Normal(n=41), overweight (n=44), obese class I(n=40) , class II(n=38) and Class III (n=35) women
Non-anomalous, Singleton, cephalic
GA 36 – 42 weeks
Ultrasound EFW 48 hours prior to scheduled delivery
The highest mean absolute error of sonographic fetal weight estimation was 446±151 grams in class III obese (MAPE 14±5)
They did not specify in the study the number of previous cesarean sectionss

8. Ultrasound EFW Vs Clinical EFW
Ultrasound estimation of fetal weight is not superior to clinical estimation in the obese population.
Both methods have an associated error of approximately 10%, in the series reported by Field et al., 30% of obese women had an ultrasound estimated fetal weight within 5 days of delivery that was > 10% different from the actual birth weight.
When comparing ultrasound EFW and clinical
Field NT et al. Obstet Gynecol 1995

9. HOW TO SCAN HEAVY WOMEN?
Check the average BMI of patients coming to FMU over a week. Ask nurses to make sure its recorded in Astria

10. 1- Be Considerate and Non-Judgmental

11. 2- Explore the alternatives

12. When and How?
Performing transabdominal examination later in gestation (20 to 22 weeks) in the obese gravida may improve visualization of anatomy.
Transvaginal ultrasound of fetal anatomy may be more effective earlier.
Reddy, U. M., et al. Obstet Gynecol,2014

13. Methods
Gel : prevents air from coming between the transducer and the patient. The gel also permits the ultrasound probe to gently slide over the abdomen or along the vagina.
Transducers and probes: It is important to keep in mind that higher frequency transducers provide superior resolution, but have less tissue penetration. This trade-off is important for achieving images of diagnostic quality.
Transducers and probes: The transducer is located inside the ultrasound probe. The most common transducers used for transabdominal scanning are sector or curvilinear transducers that have frequencies up to 7.0 or 8.0 MHz. Transducers used for transvaginal scanning typically have frequencies up to 9.0 MHz. It is important to keep in mind that higher frequency transducers provide superior resolution, but have less tissue penetration. This trade-off is important for achieving images of diagnostic quality.
Tempkin BB. Ultrasound Scanning: Principles and Protocols, 2nd ed, WB Saunders Co, Philadelphia 1999

14. Technical Issues & solutions:

16. Acoustic limiting factors in obese mothers:
Increased depth of insonation required and the absorption of ultrasound energy (dropout) by the abdominal adipose tissue.
The greater distance that the ultrasound waves have
to travel means greater absorption and dispersion in the
surrounding tissues. At the end of their journey, the ultrasound waves are weaker, having lost a significant amount of energy, and the backscatter from refraction is much higher. As a consequence, the signal-to-background
noise ratio is also decreased.
Paladini, D. Ultrasound Obstet Gynecol 2009

17. To deal with these problems:
Ultrasound equipment producers have followed two lines of action.
1- Reducing the mean array emission frequency to warrant better penetration.
Paladini, D. Ultrasound Obstet Gynecol 2009

18. 2- Use pre- and postprocessing filters and techniques to increase the signal-to-background noise ratio which include: A- Tissue harmonic imaging, which increase with depth. B- Spatial compounding reduces speckle artifacts and improves contrast resolution. C- Speckle reduction filters are post-processing tools that further improve image quality and contrast.
Paladini, D. Ultrasound Obstet Gynecol 2009

25. 3- Acknowledgement of Scanning Limitations
We are still in how to scan heavy women

26. Total twins= 300
Normal BMI 179, Overweight 67, Obese 54. GA >28 weeks
Increased MAPE for both twins in the obese compared to normal weight if delivery happened between 8 and 14 days from ultrasound,
,(twin A) 19 Vs 5%, (twin B) 13 Vs 3, P < 0.05.
This difference was diminished if the ultrasound was performed within seven days of delivery. The ultrasound detection of inter-twin weight discordance was similar among the three BMI groups.
Al-Obaidly, S. et al. J Obstet Gynaecol Can 2015

27. 106 Obese patients with recorded BMI≥30 kg/m2, class I and II (BMI kg/m2) compared with Class III, IV and V (BMI ≥40 kg/m2), who gave birth after 28 weeks gestation of viable singleton, who had an ultrasound within 7 days of delivery with reported normal amniotic fluid and no major fetal anomaly; the EFW was consistently measured through Hadlock regression formula over one year period. Differences between the EFW and actual birth weight (ABW) were assessed by percentage error, accuracy in predictions within ±10% of error and the Pearson correlation coefficient was used to correlate EFW with the ABW. Class I and II as the first group (n= 53). Class III as the second group (n= 53). The average gestational age (GA) at birth was 36 ± 2 weeks for both groups (p=0.5). The average EFW in grams were 2804 ± 691 and 2997 ± 815 for first and second groups respectively (p=0.5). The average ABW in grams were 2759 ± 756 and 3045 ± 879 for first and second groups respectively (p=0.07). The Pearson correlation coefficient equal 1 in both groups. The overall Mean absolute difference (MAD) in grams of the whole obese cohort was 242 ± 213. The MAD was 242 ± 202 and 242 ± 246 grams for first and second group respectively (p=1.0). The overall mean absolute percentage error (MAPE) in this obese cohort was 8%. The MAPE for the first and second group respectively were 9% and 8% (p=0.4)
Accepted for RCOG 2017 congress

28. Fetal Macrosomia

29. Fetal Macrosomia DIAGNOSIS:
2D ultrasound is the standard modality used for diagnosis of fetal macrosomia and LGA.
Sonography is most predictive, however not highly accurate, even when performed near the time of delivery in singleton, cephalic presenting, nondiabetic pregnancies.
EFW is not precise at any GA.
Ben-Haroush et al. Am J Obstet Gynecol 2007
Thorsell M et al. Ultrasound Obstet Gynecol 2010

30. Fetal Macrosomia Standard sonographic approach:
fetal weight is NOT a parameter that can be measured directly, but must be calculated by integrating biometric measurements into a formula.
Limitations:
Since the fetus is irregular, the ability of formulas to predict fetal weight has been limited, without good sensitivity and specificity.
Sonographic measurement does not permit differentiation between pathologically large and large but healthy infants, as is also the case for the small fetus.
Formulas for estimating fetal weight perform better for normal sized fetuses than for macrosomic ones.
Limitations:
Since the fetus is irregular, the ability of formulas to predict fetal weight has been limited, without good sensitivity and specificity.
Sonographic measurement does not permit differentiation between pathologically large and large but healthy infants, as is also the case for the small fetus.
Serial measurements can be taken over time to create individual growth curves, which enhance diagnostic accuracy.
Formulas for estimating fetal weight perform better for normal sized fetuses than for macrosomic ones.
Combs CA et al. J Matern Fetal Med 2000

31. A review of 14 studies on the sonographic detection of macrosomia (≥4000 g) in general obstetrical populations reported widely varying results: sensitivity 12 to 75 percent, specificity 68 to 99 percent.
The diagnosis of macrosomia defined as ≥4500 was even less accurate, and there were no data on the ability to identify fetuses >5000 g.
These studies used a variety of methods for sonographic estimate of fetal weight and illustrate the difficulty in accurately diagnosing macrosomia.
A review of 14 studies on the sonographic detection of macrosomia (≥4000 g) in general obstetrical populations reported widely varying results: sensitivity 12 to 75 percent, specificity 68 to 99 percent, and post test probability after a positive test 17 to 79 percent; results for populations with a high prevalence of macrosomia were at the upper end of these ranges.
The diagnosis of macrosomia defined as ≥4500 was even less accurate, and there were no data on the ability to identify fetuses >5000 g. These studies used a variety of methods for sonographic estimate of fetal weight and illustrate the difficulty in accurately diagnosing macrosomia.

32. Fetal Macrosomia Abdominal circumference:
Abdominal circumference (AC) is the most common and reliable single parameter used to assess risk of macrosomia.
It is measured on a defined plane incorporating the liver since growth abnormalities are often reflected by changes in liver size.
Abdominal circumference (AC) is the most common and reliable single parameter used to assess risk of macrosomia.
It is measured on a defined plane incorporating the liver since growth abnormalities are often reflected by changes in liver size.
The most commonly used thresholds for prediction of macrosomia are ACs of 35 to 38 cm.
The sensitivity of the AC measurement depends upon the cut-off chosen, definition of macrosomia, and gestational timing of the examination.
Rosati P et al. J Matern Fetal Neonatal Med 2010
De Reu PA et al. J Perinat Med 2008

33. Fetal Macrosomia Estimated fetal weight:
The most popular formulas are Hadlock's and Warsof's with Shepard's modification.
Comparisons of these formulas concluded that the formula using BPD, FL and AC (second Hadlock formula) resulted in the best estimate of fetal weight, while the formula using only BPD and AC (Shepard formula) had the least accurate estimate.
Ultrasound examination typically involves measurement of multiple biometric parameters that are incorporated into a formula for calculating estimated fetal weight (EFW).
Most commonly, a combination of biparietal diameter (BPD), head circumference (HC), AC, and femur length (FL) is used.
The most popular formulas are Hadlock's and Warsof's with Shepard's modification.
Comparisons of these formulas concluded that the formula using BPD, FL and AC (second Hadlock formula) resulted in the best estimate of fetal weight, while the formula using only BPD and AC (Shepard formula) had the least accurate estimate.
Hadlock FP et al. Radiology 1985
Warsof SL et al. Am J Obstet Gynecol 1977
Shepard MJ et al. Am j Obstet Gynecol 1982

34. Fetal Macrosomia
Adjusting EFW for the date of delivery, maternal weight, maternal height, and presence of diabetes yields better sensitivity and specificity than traditional unadjusted formulas, particularly in macrosomic fetuses.
Including maternal weight in weight-estimation formulas also improves the accuracy, to a mean absolute percentage error of 3.69 percent with 97.1 percent of fetuses within 10 percent of actual birth weight.
Coomarasamy A et al. BJOG 2005
Sokol RJ et al. Am J Obstet Gynecol 2000
Hart NC et al. Ultrasound Obstet Gynecol 2010

35. Fetal Macrosomia Serial measurements:
The rationale for determining individualized growth curves is that fetal measurements obtained at intervals allow construction of a growth curve specific to an individual fetus.
Possible to extrapolate from multiple points to predict birth weight.
Superiority and cost-effectiveness of this approach have not been established definitively.
Owen P et al. Ultrasound Obstet Gynecol 1998
Hedriana HL et al. Am J Obstet Gynecol 1994

36. Fetal Macrosomia Soft tissue measurements:
Adipose tissue is subject to major changes when conditions associated with accelerated or decreased growth are present.
Diabetic mothers with poor glycemic control are at increased risk of having a macrosomic infant with a large volume of subcutaneous fat
Ultrasound has been used to assess subcutaneous fat to provide better evaluation of normal and disturbed growth.
Prenatal sonographic evaluation of adipose tissue appears to have good correlation with postnatal skin fold measurements, although data are limited.
Bernstein IM et al. Obstet Gynecol 1992

38. Fetal Macrosomia
Combinations of soft tissue measurements or other parameters with EFW may be more useful for predicting macrosomia than any method alone.
Hackmon R et al. Am J Obstet Gynecol 2007

39. DIAGNOSIS OF FETAL MACROSOMIA IN DIABETIC MOTHERS
The methods for detection of macrosomia are standardized for singleton, cephalic presenting, nondiabetic pregnancies.
The methods for detection of macrosomia are standardized for singleton, cephalic presenting, nondiabetic pregnancies.
Overestimations and underestimations are more common in estimating weight in infants of diabetic mothers, multiple gestations, and breech fetuses.
O’Reilly-Green et al. Clin Obstet Gynecol 2000

40. Diabetic mother
The growth pattern of fetuses of women with diabetes, especially when glycemic control has been poor, is different from that in fetuses of nondiabetic mothers.
Macrosomic infants of diabetic mothers have larger shoulders and greater amounts of body fat
Several studies have used this information in an attempt to predict the risk of shoulder dystocia in diabetic pregnancies, but no method has proven to be reliable.
The growth pattern of fetuses of women with diabetes, especially when glycemic control has been poor, is different from that in fetuses of nondiabetic mothers.
Macrosomic infants of diabetic mothers have larger shoulders and greater amounts of body fat, decreased head-to-shoulder ratio, and increased skin folds in the upper extremities.
Several studies have used this information in an attempt to predict the risk of shoulder dystocia in diabetic pregnancies, but no method has proven to be reliable.
Durnwald C et al. Am J Obstet Gynecol 2004

41. Diabetic mother
Ultrasound prediction of EFW in fetuses of diabetic mothers tends to overestimate fetal weight since the EFW formula is very sensitive to measurement of AC, and AC is increased in these fetuses.
The mean absolute percent error (MAPE) is greater in infants weighing above 4500 g (12.6 versus 8.4 percent if below 4500 g)
Regardless of diabetic status. Customized formulas for use in diabetic mothers have generally not been proven to be beneficial, although the FL/AC ratio (X100) appears to be useful for prediction of macrosomic infants in diabetic mothers.
Landon MB et al. J Matern Fetal Med 2000

42. Diabetic mother
A study reported that AC >70 percentile is predictive of poor glycemic control and increased risk of macrosomia.
Based on these findings, the American Diabetes Association recommended the use of AC >75th percentile as a measure of glycemic control and risk for macrosomia in diabetic gravidas.
Metzger, B. E., et al. (2007). "Summary and recommendations of the Fifth International Workshop-Conference on Gestational Diabetes Mellitus." Diabetes Care 30 Suppl 2: S

43. Congenital Anomalies

44. Congenital anomalies in Obese
Based on several metanalysis, maternal obesity appears to be associated with a small increase in the absolute rate of some congenital anomalies
and the risk may increase with increasing maternal weight.
The mechanism for the association is not known, but is likely related to an altered nutritional milieu for fetal development, including hyperinsulinemia.
Stothard KJ et al. JAMA 2009
Rasmussen SA et al. Am J Obstet Gynecol 2008
Cai GJ et al. Am J Obstet Gynecol 2014

45. There are several limitations to the available data.
congenital anomalies are more difficult to detect with prenatal ultrasound in obese women, resulting in fewer antepartum diagnoses and, in turn, fewer pregnancy terminations.
Maternal obesity lowers the detection of fetal anomalies by at least 20 percent compared with women with a normal body mass index.
Although most studies attempted to adjust for confounders, adjustment factors varied among the studies.
Hendler I et al. Int J Obes Relat Metab Disord 2004
Aagaard TKM et al. Prenat Diagn 2010
Best KE et al. BJOG 2012

46. Pregestational diabetes is associated with both obesity and risk of congenital malformations, failure to ascertain and adjust for pregestational diabetes could bias the findings .
Criteria for obesity and ascertainment of obesity were not consistent across all of the studies
Biggio JR et al. Obstet Gynecol 2010

47. SOGC 2010
The sonographer’s ability to evaluate fetal structures is largely dependent on maternal size. Approximately 15% of normally visible structures will be suboptimally seen in women with a BMI above the 90th percentile.
The anatomic structures commonly less well seen with increasing BMI include the fetal heart, spine, kidneys, diaphragm, and umbilical cord.
Repeat examinations 2 to 4 weeks later to assess the fetal cardiac anatomy will reduce the number of suboptimally viewed fetuses; however, 12% to 20% (depending on BMI class) will remain poorly visualized.
Wolfe HM et al. Obstet Gynecol 1990
Hendler I et al. Ultrasound Med 2005

48. HUMAN FACTORS AND ERGONOMICS
Repetitive motion associated with scanning or patient obesity.
Proper positioning and posture, applying excessive force, and overuse.
Proper table positioning and height, avoidance of twisting of the neck or trunk
Positioning the patient very close to the clinician and meticulously avoiding abduction of the scanning arm.
Some aspects of the sonographic examination that can lead to pain and musculoskeletal dysfunction may not be modifiable by the clinician, eg, the repetitive motion associated with scanning or patient obesity.
Many other aspects, can be modified to decrease the risk of musculoskeletal disorders. These include proper positioning and posture, applying excessive force, and overuse.
Many factors are important for proper positioning, but the most important are proper table positioning and height, avoidance of twisting of the neck or trunk and, most importantly, positioning the patient very close to the clinician and meticulously avoiding abduction of the scanning arm.
Baker, J. P. et al. J Ultrasound Med 2013

49. Take Home Message
Maternal obesity can significantly reduce the accuracy of sonographic fetal weight estimation.
2D ultrasound is the standard modality used for diagnosis of fetal macrosomia and LGA.
Hadlock's formula has a higher predictive value than other methods.
Combinations of soft tissue measurements with EFW may be more useful for predicting macrosomia than any method alone.
Ultrasound prediction of EFW in fetuses of diabetic mothers tends to overestimate fetal weight since the EFW formula is very sensitive to measurement of AC, and AC is increased in these fetuses.
maternal obesity appears to be associated with a small increase in the absolute rate of some congenital anomalies and the risk may increase with increasing maternal weight.

50. THANK YOU