Overweight Pregnant Women Need More Ultrasounds


Obesity has increased dramatically worldwide over the last two decades, becoming a social concern. In pregnancy, obesity is associated with increased risk of maternal death and of significant complications, such as pre-eclampsia, diabetes and postpartum hemorrhage.

Several papers have also reported an increased risk of major anomalies in the offspring of obese pregnant women. At the same time, carrying out an ultrasound examination on an obese pregnant woman is a difficult task, due to the impaired acoustic window.

(c) 2009 ISUOG.

Overweight Pregnant Women Need More Ultrasounds

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Introduction and Scope of the Problem Previous sectionNext section

Obesity is a major global public health concern, with rising trends in obesity in virtually all age groups. In the United States, over 60% of women are overweight or obese with just over one third considered frankly obese [1]. Thus, obesity has become the most common clinical risk factor in obstetric practice, placing approximately 40% of pregnant patients into a high-risk category, with the resultant increased burden on our health care systems.

The expertise required to provide high-quality imaging for the obese pregnant woman is crucial given the increased maternal and fetal morbidity and mortality. Simply put, as the degree of maternal obesity increases, risks to mother and fetus increase while our ability to optimally image this population decreases.

What Is Obesity?

The most practical and commonly used definition of obesity is a body mass index (BMI) greater than 30 kg/m2 [2] (Table 1). Nonetheless, many experts believe that obesity represents the visible symptom of a complex medical entity referred to as the “metabolic syndrome,” which incorporates associated conditions such as insulin resistance, dyslipidemia, and diabetes mellitus. As shown in Figure 1, children of obese parents are at high risk of adulthood obesity; thus, the health care burden is anticipated to progressively increase in the future. In response to this challenge, a number of so cieties, including the American, Canadian, and British colleges of obstetricians and gynecologists, have recently published guidelines for managing obese pregnant women [35].

Data table

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TABLE 1:Body Mass Index Classification

Despite antiobesity drugs, dietary, and exercise regimens, the only effective long-term means of controlling severe obesity remains bariatric or weight loss surgery. As most pregnancies are unplanned, there is often not enough time to implement effective dietary and exercise plans. Furthermore, antiobesity drugs and bariatric surgery are not appropriate for the pregnant woman. Pregnancy is a unique time in a woman’s life where she may feel especially motivated to adhere to strict weight gain guidelines. In 2009, the Institute of Medicine revised pregnancy weight guidelines such that obese women are advised to gain 11–20 pounds, in contrast to 25–35 pounds in the average weight pregnant population [6]. In some cases, a controlled or minimal weight gain during pregnancy may have a dramatic positive impact on pregnancy outcomes for both the mother and her baby.

What Is the Role of the Imaging Specialist?

The imaging specialist plays a central role in the management of the obese pregnant woman. This includes areas such as anatomic evaluation of the fetus, monitoring fetal well-being and the development of uteroplacental insufficiency, determination of estimated fetal weight (EFW), ultrasound guidance of neuraxial anesthesia, and managing the imaging options for maternal complications that may occur during pregnancy or the postpartum period. Although ultrasound remains the initial imaging study of choice, the imaging specialist must judge whether the limitations imposed by an obese body habitus warrants additional imaging techniques such as MRI [7, 8]. Detailed knowledge of ultrasound image optimization parameters, new algorithms, software, and hardware options may convert a suboptimal examination into a diagnostic evaluation. In particular, it is important to communicate to obese pregnant patients the reality of the limitations of an obstetrical ultrasound evaluation.

Maternal Risks Associated With Obesity Previous sectionNext section

Obesity is an independent risk factor for adverse maternal obstetrical outcome [9]. Consequences of maternal obesity in pregnancy are listed in Table 2 [3, 4, 1012].

Data table

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TABLE 2:Maternal Risks of Obesity

Many obese women have already faced significant health challenges before they arrive for the first ultrasound evaluation. These may include ovulatory infertility, increased fetal wastage, hypertension, diabetes, venous thromboembolism, cardiorespiratory disease, and obstructive sleep apnea. Maternal obesity is also associated with increased rates of complications in late pregnancy, including gestational diabetes, preeclampsia, nonprogression of labor, shoulder dystocia, and cesarean section [1118].

Given the potential difficulties in performing an emergent cesarean section in the morbidly obese patient, a prescheduled procedure with preoperative consultations may be preferred. Difficulties in achieving intubation, line placement, and neuraxial anesthesia may prolong and complicate the process, especially in the urgent setting. Despite the difficulties in placement of an epidural needle, general anesthesia is generally avoided to reduce the difficulties of intubation and high ventilation pressures, which may result in barotrauma. During cesarean section, the abdominal pannus may need to be retracted or harnessed cephalad. In women in the 350-pound range or more, the pannus may weigh as much as 100 pounds, and displacing this weight upward on the maternal abdomen may compromise the mother’s breathing [19]. Ultrasound guidance of neuraxial analgesia is being used to enhance the accuracy of needle placement [20] (Figs. 2A, 2B, and 2C).

Pregnancy and the puerperium are well established risk factors for venous thromboembolism, primarily on the basis of venous stasis, hypercoagulability, and vascular damage. The risk is greatest postpartum. Pulmonary embolism (PE) is a significant cause of maternal mortality [21]. Both obesity and pregnancy are independent risk factors for the development of deep venous thrombosis and PE, with the risk for the obese pregnant patient 1.4–3.6-fold that of normal weight pregnant women [11, 10, 22].

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Fig. 1Schematic of metabolic syndrome and effects on fetal and childhood development.

The recommended diagnostic strategies for deep venous thrombosis and PE are the same in both the pregnant and nonpregnant populations [23]. Although every effort is made to avoid fetal exposure to radiation, these concerns should not prevent the appropriate diagnostic evaluation [8]. The estimated mean radiation dose of CT angiography to the fetus is 3–131 μGy across pregnancy, less than those calculated for ventilation–perfusion scanning (680–800 μGy) [24]. The combination of automatic tube modulation with commercially available breast shields, such as tungsten in-line shields, can provide significant reduction in radiation dose to the breast without substantial deterioration in image quality [25, 26]. In the obese pregnant population, there is limited information available to guide physicians on the relative degradation and increase in nondiagnostic evaluations for compression ultrasound, CT, MRI, or ventilation–perfusion imaging [27]. MRI has been shown to be highly sensitive and specific for evaluation of pelvic veins in the nonpregnant population and may have a role to play in the obese pregnant population.

The safety of MRI during pregnancy has not been proven, although no adverse effects have been documented to date; thus, an informed choice process is recommended. According to the American College of Radiology, the utilization of MRI is growing faster than any other imaging technique [28]. Although documentation is more limited, MRI utilization is also on the rise during pregnancy.

Because MRI is less affected by obesity than ultrasound, we anticipate it will progressively become a basic tool of investigation for complications of pregnancy. The current generation of MRI technology can provide relatively short bores with larger vertical diameters (70 cm), tables that can accommodate patients weighing up to 550 pounds, and MRI units that operate at 1.5-T strengths with significant improvements in image resolution compared with previous generations of “open” magnets. CT scanner capacities have “upsized” from maximum gantry diameters of 70 cm to as high as 90 cm and table capacities of up to 680 pounds. The variation in geographic distribution of these “upsized” CT and MRI units may affect patient referral patterns and care outcomes. Future prospective studies are required to establish a correlation between BMI and image quality for each technique. This would be helpful in directing radiologists to perform the most appropriate test in a given clinical situation.

Fetal Risks of Maternal Obesity Previous sectionNext section
Congenital Fetal Abnormalities

The increased risk of fetal structural anomalies remains independent of other maternal risk factors such as diabetes [2931]. The ultrasound diagnosis of a fetal anomaly presents a special challenge in the obese gravida for two main reasons: she is more likely to carry a fetus with a congenital anomaly, and the imaging of her fetus is technically more difficult. With regard to anomalies, the major anatomic areas of concern are the neural tube and heart. The two largest retrospective cohorts as well as a meta-analysis examining the relationship between maternal obesity and the risk of neural tube defects concluded that there is a direct correlation between maternal BMI and the risk of neural tube defects of 1.3–3-fold [3234] (Table 3). This risk persisted in obese women even after the widespread folic acid fortification in the 1990s [33].

Data table

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TABLE 3:Fetal Risks of Maternal Obesity

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Fig. 2A27-year-old normoglycemic obese gravida one patient was transferred to high-risk center for elective cesarean induction at term (38 weeks’ gestation). Biometry performed at 36 weeks’ gestation gave estimated fetal weight {amp}gt; 5,000 g. In view of risk of birth trauma, shoulder dystocia, and potential technical difficulties that might be encountered in emergency cesarean section, patient declined trial of labor. Preoperative ultrasound was performed to determine depth for insertion of epidural needle. Arterial line insertion was required preoperatively to permit reliable monitoring of vital signs. Abdominal pannus was harnessed to ceiling to avoid weight of panniculus compromising ventilation. Total procedure time was approximately 5 hours. A 6700 g baby was delivered. In ultrasound sagittal image, sonographic depth to fetal face was ∼11 cm.

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Fig. 2B27-year-old normoglycemic obese gravida one patient was transferred to high-risk center for elective cesarean induction at term (38 weeks’ gestation). Biometry performed at 36 weeks’ gestation gave estimated fetal weight {amp}gt; 5,000 g. In view of risk of birth trauma, shoulder dystocia, and potential technical difficulties that might be encountered in emergency cesarean section, patient declined trial of labor. Preoperative ultrasound was performed to determine depth for insertion of epidural needle. Arterial line insertion was required preoperatively to permit reliable monitoring of vital signs. Abdominal pannus was harnessed to ceiling to avoid weight of panniculus compromising ventilation. Total procedure time was approximately 5 hours. A 6700 g baby was delivered. Ultrasound was used to determine site and depth for penetration for epidural analgesia (arrows). Three attempts were required.

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Fig. 2C27-year-old normoglycemic obese gravida one patient was transferred to high-risk center for elective cesarean induction at term (38 weeks’ gestation). Biometry performed at 36 weeks’ gestation gave estimated fetal weight {amp}gt; 5,000 g. In view of risk of birth trauma, shoulder dystocia, and potential technical difficulties that might be encountered in emergency cesarean section, patient declined trial of labor. Preoperative ultrasound was performed to determine depth for insertion of epidural needle. Arterial line insertion was required preoperatively to permit reliable monitoring of vital signs. Abdominal pannus was harnessed to ceiling to avoid weight of panniculus compromising ventilation. Total procedure time was approximately 5 hours. A 6700 g baby was delivered. Retraction of panniculus was achieved by combination of harnesses both retracting and vertically suspending abdominal panniculus to ceiling hook (arrow). Photographs reproduced with patient permission.

In a U.S. study of over 7,000 cases of congenital heart defects, the presence and severity of maternal obesity increased the risk of having a child born with the abnormality [35]. The most recent data from the U.S. National Birth Defects Prevention Study confirmed that the higher the BMI, the greater the risk of congenital heart disease [36].

Stothard and colleagues [37] performed both a systematic review and meta-analysis of multiple studies involving maternal obesity and fetal anomalies and concluded that odds were greater for not only cardiac defects but also cleft lip and palate, anorectal atresia, hydrocephaly, and limb reduction anomalies. Interestingly, the risk of gastroschisis was significantly lower in fetuses of obese women.


One of the underappreciated risks of maternal obesity is the propensity of the fetus to become macrosomic and the challenge of accurately assessing EFW at the upper extremes of fetal weight. Macrosomia is a well-known risk factor for adverse events surrounding delivery, including postpartum hemorrhage, anorectal sphincter lacerations, increased risk of cesarean section, fetal injury associated with shoulder dystocia, asphyxia, and prolonged labor (including studies from Sweden [18], Denmark [38], United States [3941], United Kingdom [42], and Argentina [43]). The higher the degree of maternal obesity, the greater the risk for these adverse outcomes.

Shoulder dystocia and birth injury risks increase sharply with increasing fetal macrosomia, risks further augmented by the presence of maternal diabetes [44, 45] Most authors favor an EFW greater than 4,000–4,500 g as a reasonable definition of macrosomia with an estimated risk of shoulder dystocia commonly quoted as about 5% at 4,000 g and increasing to 30% by 4,500 g; thus, obstetricians tend to counsel to early induction of labor or cesarean section on the basis of the EFW. In contrast to the clear clinical impact of macrosomia, the ability to accurately estimate fetal weight at the upper extremes is relatively low, with errors exceeding 10% of the birth weight [46, 47].When birth weight is greater than 4,500 g, only half of the fetuses will fall within 10% of the EFW. In other words, EFW needs to exceed 4,800 g in order for 50% of the fetuses to achieve the 4,500-g cutoff designated as macrosomia [48, 49]. Significant refinements of EFW formulae are required to improve the accuracy of EFW predictions at the upper extremes of birth weight. It is important to inform the patient and her care team that the ultrasound evaluations may be limited, in particular on the basis of suboptimal visualization and inaccurate EFW at the upper extremes of fetal weight, to limit legal liability.

Obesity is an independent risk factor for stillbirth (as much as a three-fold risk) [50, 51]. It is speculated that the accelerated fetal growth induced by the endogenous hyperinsulinemia in obese women, in combination with uteroplacental insufficiency, may lead to fetal hypoxia and death.

Quality of Patient Care: Limitations of Ultrasound, Ergonomic Issues, Imaging Tips, and Patient Safety Previous sectionNext section
Limitations of Ultrasound During Visualization of Fetal Anatomy

The sonographer tasked with examining the fetus of the obese gravida is likely to be aware of the fact that the scan may be difficult or impossible to complete. Data collected for over 8,000 women as part of the FaSTER trial in the United States showed that detection rates of cardiac anomalies were significantly lower and the missed diagnosis rate for multiple aneuploid markers was significantly higher in obese women [52]. Investigators in the United States [5356] and Canada [57] have shown suboptimal visualization rates ranging from 20% to 50% in obese women at the time of fetal anatomic scanning in the second trimester, mostly involving the cardiac and craniospinal structures.

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Fig. 3AIllustrative images of potential advantages of transvaginal ultrasound. Routine transabdominal image of fetal abdomen at 20 weeks provides limited detail. Note overlying extensive abdominal pannus.

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Fig. 3BIllustrative images of potential advantages of transvaginal ultrasound. Fifteen-week transvaginal image of fetal abdomen provides detailed image of abdominal structures.

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Fig. 3CIllustrative images of potential advantages of transvaginal ultrasound. Routine transabdominal of fetal heart at 20 weeks provides good anatomic detail.

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Fig. 3DIllustrative images of potential advantages of transvaginal ultrasound. Fifteen-week transvaginal image of fetal heart provides excellent detail.

Despite all maneuvers, visualization can remain limited with decreased completion rates for the anatomic survey in the obese pregnant patient. Studies have variably shown that delaying, repeating, or increasing the duration of the examination may only partially, if at all, mitigate the technical limitations that obesity imposes on visualization [30, 53, 58]. There is a growing body of evidence showing that fetal anatomic evaluation in the average weight gravida can be accomplished via the transvaginal route in early pregnancy, resulting in a trend to providing prenatal diagnosis in the late first [5962] or early second trimester [63]. Imaging of the heart is possibly the most controversial area with respect to timing. Although one can begin to evaluate the fetal heart as early as 13 weeks, there is no doubt that the larger the heart is, the easier it is to image. Yagel et al. [64] performed over 6,000 fetal echocardiography examinations at 13–16 weeks and found that full cardiac anatomy could be visualized in 95% of cases at 11–12 weeks and in 100% of cases at 13–15 weeks’ gestation, when the fetus was in a favorable position during the transvaginal ultrasound study [6466]. For the obese population, we speculate that early fetal anatomic assessment by transvaginal ultrasound may provide the only satisfactory window for evaluating fetal anatomy (Figs. 3A, 3B, 3C, and 3D).

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Fig. 4Patient who presented for 19-week routine anatomy ultrasound examination. Note overhanging abdominal pannus, which will require lifting for much of examination (arrow). It is important to engage patient and her partner in lifting to minimize ergonomic stress on sonographer. Photograph reproduced with patient permission.

For nuchal translucency measurements, transabdominal and transvaginal readings are generally in agreement and are not affected by maternal BMI [67]. Although imaging the fetal nasal bone may be more problematic and the use of transvaginal ultrasound is more frequently needed, nuchal translucency measurement has not been associated with suboptimal visualization in the obese gravida [68].

Ergonomic Issues in Ultrasound: An Occupational Hazard

It is important to acknowledge the special challenge for sonographers involved in imaging of the obese gravida patient. Even when good ergonomic practices are applied [69, 70], the key risk factors associated with work-related musculoskeletal disorders, such as repetitive motion, forceful or awkward position, prolonged duration of pressure, and improper positioning, may still exist. The reality is that, despite best practices, additional strategies may be required. Lifting devices to remove the pannus from the groin have been developed for surgical procedures. Future developments may lead to similar devices modified for use in performing obstetrical ultrasound (Fig. 4).

Imaging Tips and Patient Safety

The obese gravida should be placed in an oblique or decubitus position to avoid the risk of aortocaval compression with secondary hypoxemia and hypotension due to the combination of uterine enlargement and a heavy abdominal pannus, which can weigh more than 100 pounds in the morbidly obese patient. A semirecumbent position may improve pulmonary mechanics and help avoid a hypoxic episode.

The abdominal pannus acts to limit visualization both by actual depth of insonation required and the increased absorption of ultrasound energy by the adipose layer associated with decreased energy and increased backscatter, resulting in an image with decreased signal-to-noise ratio [71]. A basic element of good imaging technique is placing the organ of interest, in this case the fetus, as close as possible to the transducer. The abdominal pannus is generally thickest between the pubic symphysis and the umbilicus; thus, scanning above or below may be helpful. Scanning through the umbilicus provides an imaging window through the thinnest part of the abdominal wall [72] (Figs. 5A and 5B). Turning the patient into a decubitus position causes the abdominal pannus to fall away, providing a better window at the lateral flank when pointing the transducer medially. Basic maneuvers such as repositioning the transducer to improve scan angle, avoiding reverberation artifact, and narrowing the sector width to improve resolution should be used. Advanced technology such as harmonic imaging to improve edge resolution, compound imaging to reduce angle-generated and speckle noise artifacts, and postprocessing techniques to provide imaging enhancement with improved signal-to-noise ratios and improved margin definition have proven to be helpful [71]. More recently, lower frequency transducers (1 MHz) coupled with adaption of beam-forming algorithms to better model overweight patients and tissue aberration correction programs to adjust for speed of sound in adipose tissue are permitting both greater depth of penetration and resolution in this population. The development of new crystal array transducers and isotropic transducers that allow real-time multiplanar imaging may prove to be helpful in the obese gravid population. MRI is proving useful for the evaluation of the obese gravida because it is less affected by obesity than ultrasound is. Gorincour and colleagues [73] performed a post hoc analysis of patients with normal BMI who had undergone MRI for various fetal indications and examined the images for feasibility of completing fetal cardiac anatomy. The results were promising for the 10 subjects they studied, and the authors pointed out that obesity per se should not alter the visualization with MRI. Newer techniques, developed in animal models, of self-gating and pulse-wave-triggered cardiac MRI are promising for evaluation of cardiac anatomic structures and functional information [74].

Future of Imaging in the Obese Gravida Previous sectionNext section

The trend toward early fetal diagnosis has been advocated more extensively in Europe than in the United States, perhaps in part because of a challenging learning curve [61]. In the obese population, we speculate that this may be the only satisfactory window for evaluating fetal anatomy. Whether ultimately this is the best direction will depend in part on the development of lower frequency transducers and algorithms to better model obese patients, thus improving the success of the routine mid-second-trimester ultrasound. In addition, the availability of large-bore magnets with 1.5-T capabilities for MRI are proving useful in static image acquisition. Newer techniques with wave-triggered cardiac MRI are promising for evaluation of cardiac structures in normal weight patients and promising for the obese gravida.

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Fig. 5AIllustrative example of utilizing transumbilical window to improve imaging in 22 weeks’ gestation fetus. Ultrasound image was obtained through abdominal pannus through subcutaneous depth of 5 cm.

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Fig. 5BIllustrative example of utilizing transumbilical window to improve imaging in 22 weeks’ gestation fetus. Ultrasound image was obtained through umbilicus through subcutaneous depth of only 2.8 cm with accompanying improved resolution.

Prediction of Stillbirth, Intrauterine Growth Restriction, and Preeclampsia in Obese Pregnant Women

Investigators such as Gardosi [75] have suggested that the increase in stillbirth in obese pregnancies may be due in part to unrecognized fetal growth restriction when conventional growth standards are used. Groups in The Netherlands [76], Sweden [77], and the United Kingdom [78] have suggested utilizing customized growth curves. Obese women may benefit from screening with umbilical or uterine artery Doppler velocimetry to predict adverse pregnancy outcome.

Laser Doppler Velocimetry

Stewart et al. [79] studied microvascular function in obese women during the first trimester by use of laser Doppler perfusion scanning of endothelium. They observed impaired endothelial function and chronic endothelial activation. An exciting future application of this noninvasive technique is the ability to identify a potentially high-risk group of obese pregnant women with an underlying inflammatory vascular state. This inflammatory vascular state is postulated to affect both uteroplacental and maternal systemic circulation, potentially resulting in fetal growth restriction, maternal preeclampsia, thrombocytopenia, renal impairment, and hepatic dysfunction on the basis of microvascular multisystem end organ damage.

Diabetes and Obesity in Pregnancy

Obesity is an important risk factor for both pregestational and gestational diabetes [80, 81]. Maternal hyperglycemia is a potent fetal cardiac teratogen [82, 83]. Measurement of the visceral fat by transabdominal ultrasound in the first trimester is positively correlated with abnormal glucose challenge testing in the third trimester [84]. This ultrasound screening could be used to identify those women at greatest risk for gestational diabetes earlier and impact the onset of diagnostic testing and treatment.

Multiple Gestation

There are very limited data on multiple pregnancy outcomes in obese gravidas. Obesity does not appear to influence rates of prematurity, growth discordance, or birth weight less than 2,500 g, although increased risk of still-birth and hypertensive disorders are documented [85, 86]. The estimation of EFW, in particular for Twin B, has been shown to be decreased in accuracy. This has potentially grave implications on the obstetrician choosing the safest mode of delivery (i.e., vaginal or operative route). Clearly, as our pregnant population becomes older, potentially more overweight and obese women will use artificial reproductive technology, and thus more multiple pregnancies are likely to be affected by obesity.

Labor and Delivery Management

Obese pregnant patients are more likely to experience complications during regional anesthesia placement [87, 88] (Figs. 2A, 2B, and 2C). However, epidural and spinal anesthesia are preferred to general anesthesia given the considerable risks with failed intubation, difficulty with ventilation, and potential for barotrauma in the obese gravida. Ultrasound measurement of the epidural space depth has been shown to improve the placement, quality, and patient experience of epidural anesthesia in small studies [20, 89, 90].

Short- and Long-Term Implications of Maternal Obesity on the Next Generation

Macrosomic infants have a nine-fold increased risk of adult obesity and development of the metabolic syndrome. Infants who had an accelerated fetal growth pattern are fivefold more likely to become obese adults [91]. In the U.S. Growing Up Today Study, a cohort study of over 14,000 adolescents, a 1-kg increment in birth weight among full-term infants was associated with a 50% increase in the risk of overweight at ages 9–14 years [92]. It is speculated that maternal obesity, hyperglycemia, and the metabolic syndrome may result in a vicious cycle leading to fetal hyperinsulinemia, which in turn may reset the CNS appetite regulation centers leading to future hyperphagia (overeating) with impaired glucose tolerance. This in turn leads to a hypothalamic form of insulin resistance with alterations in neurotransmitter production for satiety promoting obesity and the metabolic syndrome in the child of an obese mother. Thus, macrosomic infants and children of obese mothers are at significantly increased risk to become obese adults and develop the metabolic syndrome.

Summary Previous sectionNext section

Obesity is a major health challenge for our society, and both radiologists and obstetricians will face an increasing number of pregnancies affected by this condition. Important issues that require further investigation include the optimization of fetal scanning and prenatal screening, estimation of fetal weight, and the potential role of MRI in both maternal and fetal diagnosis.

The estimated annual health care cost due to obesity is estimated to approach $39–100 billion [93]. Obesity in pregnancy will have an increasingly significant impact on health care resources in the future. Urgent action is needed to help diagnose and treat the complications of this epidemic to make pregnancy management and childbirth safer for our mothers and infants.

From a public health perspective, obesity is an important modifiable risk factor for adverse maternal and fetal outcome, beginning in the womb with lifelong and even multigenerational impact. Given that the only successful long-term therapy for obesity appears to be bariatric surgery, research into prevention rather than treatment should be our priority.

NEW YORK, New York — Pregnant women who are morbidly obese may need more time during their ultrasound appointments and more frequent visits because their babies may be difficult to image, researchers report.

«There’s a real prevalence of obesity in women of reproductive age; nearly one third of women are obese.» In addition, nearly 8% of these women are morbidly obese, with a body mass index of more than 40 kg/m², said Robert Ehsanipoor, MD, from the Johns Hopkins University School of Medicine in Baltimore, Maryland.

He presented the study results here at the American Institute of Ultrasound in Medicine 2013 Annual Convention.

Excess weight is associated with an increase in risk of as much as 20% for antepartum, intrapartum, and postpartum congenital anomalies, and the detection rate of these anomalies is much lower in obese women than in healthy-weight women. «Historically, you are likely to complete only half an anatomy survey on the first attempt,» Dr. Ehsanipoor noted.

To determine the actual time required to properly complete an anatomic survey, Dr. Ehsanipoor and his team conducted a retrospective review of women with singleton pregnancies at their institution. All 306 underwent a detailed anatomy survey when their fetus was a gestational age of 18 to 28 weeks.

The researchers relied on self-reported height and weight to determine BMI in the study population. Obesity was defined as a BMI from 30.0 to 39.9 kg/m²; morbid obesity was defined as a BMI of at least 40 kg/m².

The time required for the exam was determined by subtracting the time of the first image from the time of the last image. This was correlated with the total number of exams dedicated to the anatomy survey.

Cases in which fetal anomalies were reported were excluded from the analysis, as were ultrasound scans for fetal growth and fetal echocardiograms.

In general, as obesity increased, so did the number of exams required to compete the anatomy survey.

Table. Fetal Anatomy Survey (n = 306)

Outcome Not Obese Obese Morbidly Obese P value
Total ultrasound time (min) 39.2 47.3 61.2 .01
Complete anatomy survey on initial attempt, n (%) 76 (79) 40 (60) 3 (18) {amp}lt;.01
Exams needed to complete anatomy survey, n (%) 1.2 (0.4) 1.4 (0.6) 2.1 (0.7) .01
Satisfactory survey, n (%) 218 (98) 61 (91) 12 (71) {amp}lt;.01
All anatomy visualized, n (%) 96 (43) 24 (36) 1 (6) {amp}lt;.01

Dr. Ehsanipoor suggested that morbidly obese women should be scanned at a later gestational age. «Another option would be to schedule short visits early in the second trimester for major anomalies and then bring them back. Do that rather than schedule a 45-minute visit in which you’re not able to see anything.»

During the same session, Timothy Canavan, MD, from the University of Pittsburgh in Pennsylvania, reported a counterintuitive finding — that babies of obese mothers are not any heavier than those of normal-weight mothers.

More Time, But No More Weight

«I do a lot of research on how obesity affects ultrasound imaging and, statistically, how it affects fetal growth. Despite everyone’s concern that obesity dramatically affects fetal growth and well being, it actually does not,» he explained.

Dr. Canavan developed a 2-level liner modeling approach that used the fetus itself as a control. For the analysis, a retrospective review of serial biometry in the second and third trimesters from 246 normal-term singleton fetuses was performed. These data were then compared with the mother’s BMI.

Linear regression analysis of second-trimester growth indicated no significant relation between fetal growth rate and BMI.

«It just doesn’t have as much effect as people thought,» said Dr. Canavan.

Dr. Ehsanipoor and Dr. Canavan have disclosed no relevant financial relationships. Despite the shared last name, Dr. Canavan is not related to the reporter of this news story.

American Institute of Ultrasound in Medicine (AIUM) 2013 Annual Convention: Abstracts 1521317 and 1540992. Presented April 9, 2013.

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