Obstetric Imaging in Obese Pregnant Women

Phyllis Glanc, Cynthia Maxwell
US Obstetrics & Gynecology, 2011;6(2):93-5
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Abstract

Obesity has been identified as a major global health concern and affects an increasing proportion of pregnant women. Pregnant obese women are at risk of a number of health problems, including hypertension, diabetes, abnormal labor, and Caesarean delivery. Fetal risks include increased rates of congenital anomalies, stillbirth, growth abnormalities, and birth trauma. Obstetrical imaging plays an important role in the assessment and management of these complications, and yet has significant limitations in quality and accuracy due to obesity itself. This review highlights the major challenges facing pregnant women and their care providers in the setting of obesity and pregnancy.
Keywords
Obesity, pregnancy, fetal ultrasound, imaging, gestational diabetes, macrosomia, intra-uterine growth restriction
Disclosure The authors have no conflicts of interest to declare.
Received: July 19, 2011 Accepted August 26, 2011
Correspondence: Cynthia Maxwell, MD, FRCSC, Staff Perinatologist, Maternal Fetal Medicine Division, Mount Sinai Hospital, 600 University Avenue, OPG 3271, Toronto, Ontario, Canada M5G 1X5. E: cmaxwell@mtsinai.on.ca

Obesity and overweight present a health challenge with staggering global impact. In 1997 the World Health Organization estimated that there are approximately one billion overweight adults and close to 300 million who are obese.1 While there is controversy as to whether obesity is truly a ‘disease’,2 it is clear that obesity is one of the most important risk factors for myriad health problems as well as pregnancy complications. Given the multifactorial nature of this condition, including a complex interaction of dietary intake and over-nutrition, inadequate physical activity, insulin resistance, diabetes mellitus and in some cases dyslipidaemia and other hormonal dysregulation, it is especially difficult to treat. Aside from monitoring nutrient intake and physical activity, there are few interventions that can be used in the treatment of obese pregnant women; bariatric surgery, the only proven effective treatment for obesity in the long term, and obesity drugs are contraindicated during pregnancy. Thus, with few solutions to a pervasive health issue affecting so many of our pregnant women, we are faced with perhaps the single biggest risk factor for pregnancy complications. Medical and obstetric issues including hypertension, diabetes, higher rates of Caesarean delivery and abnormal labour may all arise secondary to obesity during pregnancy. Furthermore, the complex interplay of obesity and hormones, nutrient transport, placental function and the intra-uterine environment place the foetus at risk of congenital anomalies, birth injury, the paradox of growth restriction in some cases and macrosomia in others, and ultimately the future risk of childhood diseases.

Imaging the obese pregnant woman poses special challenges as our ability to accurately visualise the foetus for anatomy and growth is compromised in the exact setting we anticipate finding higher rates of abnormalities. This review seeks to identify key areas of focus affecting imaging in pregnancies affected by obesity, and direct obstetrical providers to the critical areas in need of further study. The classification of obesity is given in Table 1. 3

Challenges in Foetal Assessment
In North America, many centres have adopted first-trimester or integrated prenatal screening into routine practice for all patients. Recent studies have assessed the quality of first-trimester imaging in obese women. Fortunately. most evidence suggests that the quality of the first trimester scan for nuchal translucency (NT) is satisfactory in obese women and that there is good correlation between transabdominal and transvaginal measurements. When a combination of both techniques was used, the authors were able to obtain NT measurements in all foetuses.4 A more recent study of 694 first-trimester foetuses revealed that obese women tended to need longer examinations and more frequently needed transvaginal scans.5 This study also examined the quality of nasal bone scanning, for which sub-optimal visualisation was significantly higher in obese as compared with normal-weight women.

Recent advances in first-trimester scanning suggest that completion of foetal anatomy may be feasible, although certain foetal structures such as the cavum septum pellucidum) must be examined later in gestation due to their developmental timing.6–9 The ability to visualise structures such as the heart, spine and face may be improved with a transvaginal approach in early pregnancy as compared with the routine second-trimester transabdominal scan. Thus, the impact of obesity on completion of first-trimester and early second-trimester anatomical scanning requires further study.

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