Gestational Diabetes During and After Pregnancy

14. Maternal Obesity and Epidemiological Review of Pregnancy Complications

Wanda K. Nicholson 

(1)

Department of Obstetrics and Gynecology, Centre for Women’s Health Research, University of North Carolina at Chapel Hill, Chapel Hill, MD, USA

Wanda K. Nicholson

Email: wkichol@med.unc.edu

Abstract

The epidemic of obesity in the general population is now reflected in childbearing women. Obesity was first acknowledged as a risk factor for pregnancy more than 50 years ago (Galtier-Dereure et al. Am J Clin Nutr. 2000;71:1242S-1248S), with considerable perinatal and long-term health consequences for the mother and developing fetus. Maternal obesity increases the risk of several adverse reproductive outcomes, including hypertensive disorders, gestational diabetes mellitus, cesarean delivery, thromboembolic events, postoperative morbidity, and anesthesia complications. Immediate fetal effects include difficulties with ultrasound assessment of in utero development, neural tube defects, and stillbirth. This chapter reviews current evidence linking maternal obesity with maternal and fetal complications during pregnancy.

14.1 Introduction

Both the developed wAbstract The epidemic of obesity in the general population is now reflected in childbearing women. Obesity was first acknowledged as a risk factor for pregnancy more than 50 years ago (Galtier-Dereure et al. Am J Clin Nutr. 2000;71:1242S-1248S), with considerable perinatal and long-term health consequences for the mother and developing fetus. Maternal obesity increases the risk of several adverse reproductive outcomes, including hypertensive disorders, gestational diabetes mellitus, cesarean delivery, thromboembolic events, postoperative morbidity, and anesthesia complications. Immediate fetal effects include difficulties with ultrasound assessment of in utero development, neural tube defects, and stillbirth. This chapter reviews current evidence linking maternal obesity with maternal and fetal complications during pregnancy.orld and developing countries are experiencing a rapid increase in the prevalence of adult obesity (body mass index or BMI ≥ 30 kg/m2). Globally, a 50% increase in obesity was reported from 1995 to 2000. Estimates from the International Obesity Task Force (IOTF) (http://www.iotf.org/intro/global.htm) indicate that over 300 million adults are obese and another 1 billion are overweight worldwide. Obesity in the United States has reached epidemic proportions, with an estimated 33% of women of all ages classified as obese.1 Data from the National Health and Nutrition Examination Survey (1999–2004) indicate that among nonpregnant women aged 20–39 years, approximately 25% are overweight, 28% are obese and 6% are considered extremely obese.12 About one-third (29%) of childbearing women aged 20–39 years are obese and 8% are extremely obese. With the increase in sedentary lifestyles and caloric intake in the United States, the number of overweight and obese adults is projected to rise even further over the coming decades. As such, the effect of obesity on maternal and neonatal outcomes3 is destined to become one of the biggest challenges for clinicians providing perinatal care in the twenty-first century. This chapter provides an epidemiologic review of the evidence on the effect of maternal obesity on pregnancy complications. Where possible, potential mechanistic pathways underlying the effect of obesity on each complication is presented. We include maternal and fetal complications that are specific to the prenatal period.

14.2 Defining Overweight and Obesity

The three primary measures of obesity include ideal body weight, absolute body weight, and BMI. BMI, defined as weight in kilograms per height in meters squared (kg/m2), is the most commonly used measure of obesity. It is used to estimate adiposity because of its strong correlation with fat mass. BMI is limited, however, in that it does not account for differences that may exist in fat mass by sex, age, or race/ethnicity. But for most patients, BMI is a reliable and easily usable tool to assess obesity. Clinicians can access an on-line BMI calculator for use in clinical practice at the National Heart Lung and Blood Institute website (http://www.nhlbisupport.com/bmi/).

The 1998 Clinical Guidelines on the Identification, Evaluation and Treatment of Overweight and Obesity in Adults accepts the following weight classifications for adults aged 20 years and older: underweight is defined as a BMI < 18.5 kg/m2, normal weight is a BMI 18.5–24.9 kg/m2, overweight is a BMI 25.0–29.9 kg/m2 and obesity is a BMI ≥ 30 kg/m2. The World Health Organization (WHO), National Institutes of Health (NIH) and the IOTF recommend these same threshold values in clinical practice and epidemiologic studies.4 (Table 14.1) Several early studies have used BMI values for overweight and obesity that vary from those outlined above, making it difficult to draw meaningful conclusions across studies and populations. Recent analyses, however, have consistently used the categories advocated by the NIH and IOTF.

Table 14.1

Categories of body mass index (BMI) for adults, 20 years and older

Weight category

BMI (kg/m2)

Underweight

<18.5

Normal weight

18.5–24.9

Overweight

25.0–29.9

Obesity

30.0–39.9

Extreme obesity

≥40

From data of the World Health Organization4

14.3 Obesity and Childbearing

Childbearing has been considered by many as one of the most important factors contributing to the development of long term obesity.58 Most of the weight gain with childbearing is thought to occur with the first pregnancy.67 In addition to being heavier at the time of conception, women are gaining more weight during pregnancy. One in five American women gains more than 40 pounds during pregnancy and most will retain about 40% of the weight.9Racial and ethnic subgroups of women are at greater risk for excessive gestational weight gain and gestational diabetes mellitus (GDM) compared with their white counterparts.10 In a cross-sectional analysis,11 obese African-American women had a higher likelihood of cesarean delivery (odds ratio [OR] 1.40, 95% confidence interval [CI] 1.24–1.58) and low birth weight infants (OR 1.94, 95% CI 1.57–2.40) compared to white women. Single status and high parity are associated with higher risks of weight retention, particularly among minority women.12 Rural residence has also been linked to greater risk of obesity in women.13,14 Living in nonmetropolitan areas may be related to greater postpartum weight retention.15,16

Despite the rising prevalence of obesity in childbearing women and the disproportionate number of minority women affected by obesity, there is no national source of data on obesity trends during pregnancy. The Pregnancy Risk Assessment Monitoring System (PRAMS), a population-based surveillance project supported by the Centers for Disease Control and Prevention (CDC) and state health departments, examines trends in pre-pregnancy obesity in 39 states. The Behavioral Risk Factor Surveillance System (BRFSS) is a viable source of robust regional estimates but is limited in the ability to provide national trends.

14.4 Obesity in the Nondiabetic Parturient

It is well known that pregnancy involves some degree of insulin resistance. There is a 40–50% increase in the level of insulin resistance during pregnancy and insulin resistance increases as pregnancy progresses. The influence of overweight and obesity on maternal and fetal health is thought to mirror, in some respects, the mechanisms of gestational and overt diabetes. Obesity was first acknowledged as a risk factor for pregnancy more than 50 years ago.17Recent evidence from the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study18 strongly suggest that varying degrees of hyperglycemia less than definitive GDM affect fetal development and newborn adiposity. Similar to the range of complications in obese, nonpregnant adults, maternal obesity is associated with higher risk of hypertensive disorders, development of gestational and type 2 diabetes mellitus and thrombo-embolic disease. Also, there can be difficulties with antenatal ultrasound assessment of the fetus in women with obesity. Operative complications include an increase in the likelihood of cesarean delivery, postoperative wound infection, endometritis, and anesthetic complications, including intubation and epidural placement. Newborn complications include congenital malformations, specifically neural tube defects and stillbirths.

14.5 Maternal Complications

14.5.1 Gestational Diabetes Mellitus

The etiology of GDM and the various risk factors related to the development of GDM are covered in detail in other chapters. In this section, we provide a summary of the association of maternal overweight and obesity with GDM. The prevalence of GDM ranges between 3 and 15%, depending on the diagnostic testing used, race/ethnicity of the population, and family history of type 2 diabetes. With the increase in maternal obesity, however, there has been a parallel increase in the prevalence of GDM.1921 Multiple investigations2226 have shown a higher likelihood of GDM with increasing weight, height, and BMI. The associations between obesity, hypertension, and insulin resistance in type 2 diabetes are also well recognized. However, obesity is thought to be an independent risk factor for developing GDM. Obesity has been estimated to be associated with a 20% increased risk of GDM.27 Ramos25found a twofold increase in GDM among overweight women (OR 2.0; 95% CI 1.8–2.2). Bianco22 reported a threefold increase in GDM among obese women compared with normal weight women. Further, the likelihood of GDM appears to increase substantially with increasing maternal BMI, indicating a dose–response relationship. A meta-analysis of 20 studies23 reported a pooled relative risk estimate for the likelihood of developing GDM of 2.14 (95% CI 1.8, 2.5), 3.56 (95% CI 3.1, 4.2), and 8.6 (95% CI 5.1, 16) among overweight, obese, and severely obese women, respectively, compared with normal weight women (Fig. 14.1a–c). These investigations can inform the development of clinical interventions to reduce pre-pregnancy BMI and the development of GDM.

A160858_1_En_14_Fig1_HTML.gif

Fig. 14.1

(a) Maternal overweight and likelihood of GDM (b) Maternal obesity (BMI ≥ 30 kg/m2) and likelihood of GDM. (c) Severe maternal obesity and likelihood of GDM. (Modified from Chu et. al.23)

14.5.2 Hypertensive Disorders

Maternal obesity is associated with an increased risk of hypertensive disorders of pregnancy, including chronic hypertension, preeclampsia (gestational proteinuric hypertension), and gestational hypertension. Maternal obesity with the accompanying presence of hypertriglyceridemia, hyperglycemia, and insulin resistance is thought to put the expectant mother at risk for hypertension and preeclampsia. Chronic hypertension may occur prior to conception or elevations in blood pressure may be identified for the first time during pregnancy. Hemodynamic alterations in arterial blood pressure, hemo-concentration, and cardiac function that occur more commonly in the nonpregnant obese woman also occur commonly in the obese parturient.

Findings from several large, population-based cohort studies support the association of maternal BMI with development of preeclampsia.222844 The risk of pregnancy-induced hypertension or preeclampsia is substantially greater if the mother is overweight or obese in the pregravid or early pregnancy period.30,45 Underlying mechanisms likely include the influence of elements of the metabolic syndrome, including obesity, hypertension, insulin resistance, and hyperlipidemia, on placental endothelial dysfunction. Therefore, well-designed studies examining the relation of obesity with preeclampsia account for potential confounders, including diabetes, chronic hypertension, and parity.22303537 Sebire et al33 retrospectively analyzed maternal BMI at entry into prenatal care and the development of preeclampsia in 127,213 pregnancies in northwest England. Women were categorized as normal weight, moderately obese, and very obese. Compared with normal weight women (BMI 20–24.9 kg/m2), women who were moderately obese (BMI 25–29.9 kg/m2) and very obese (BMI ≥ 30 kg/m2) had a 1.4 (1.28–1.60) and 2.14 (1.85–2.47) times higher likelihood of preeclampsia, respectively. Women at higher BMI levels were more likely to report a history of hypertension and diabetes prior to pregnancy. However, adjustment for demographic characteristics, parity, and prior history of hypertension or diabetes did not attenuate the magnitude of association between obese women and preeclampsia. Baeten et al,31 in a U.S. cohort, reported higher likelihood of preeclampsia (OR 3.3; 95% CI 3.0–3.7) among women with BMI ≥ 30 kg/m2compared with women with BMI < 20 kg/m2, after adjustment for maternal demographics, smoking status, and gestational weight gain. Among 15,262 women from the Nurses’ Health Study, Thadhani et al reported a greater likelihood of preeclampsia among women with BMI ≥ 30 kg/m2 compared with women with BMI 21–22.9 kg/m2 after adjusting for parity, diabetes, family history of hypertension, and cholesterol level. In most studies, the relation between BMI and preeclampsia increased with each BMI category, suggesting a dose–response relationship. A recent meta-analysis reported that the likelihood of preeclampsia doubled for each 5–7 kg/m2 increase in BMI.46

While it is likely that the observed association between pre-pregnancy BMI and preeclampsia is confounded by the presence of chronic hypertension, diabetes, and hyperlipidemia, the relation between BMI and preeclampsia has remained essentially unchanged after adjustment for these factors in multiple studies. Consistent with other studies of maternal obesity, pre-pregnancy BMI was based on self-reported pre-pregnancy height and weight. Also, there is heterogeneity in the BMI categories used in individual studies. Such variations make it difficult to compare results across studies or to derive a pooled estimate of the risk of preeclampsia. However, despite heterogeneity in BMI categories or potential bias in self-reported measures, there is a large body of epidemiologic studies with consistent results with multivariate adjustment for confounders.

14.5.3 Cesarean Delivery

Numerous studies report a positive association between maternal obesity and cesarean delivery.28,4749 The biological pathway through which obesity affects labor is not completely understood.50,51 Some investigators have hypothesized that obesity results in a soft tissue dystocia, where maternal pelvic soft tissue narrows the birth canal and increases the risk of failure of infant descent.47,52,53 Other studies suggest that the increased risk of cesarean is related to differences in labor progression or response to oxytocin in obese women compared with normal weight women.54 Obesity can also affect the risk of cesarean delivery through the increase in comorbidities, particularly GDM and hypertension.5556

Because of the higher prevalence of GDM in obese women, it is important to determine whether obesity increases the risk of cesarean delivery independent of GDM or whether the effect of obesity is mediated through a higher prevalence of GDM in obese women. Multiple studies consistently report a higher likelihood of cesarean delivery among obese women. Several studies have been conducted among women without GDM.49,525759 For example, Jensen et al49 reported a 1.8 times higher likelihood of cesarean (OR 1.8; 95% CI 1.6–2.2) among obese women without GDM compared to normal weight women. Two studies among obese women with GDM reported higher cesarean delivery among obese women with GDM.6061 Among seven studies25,28,33,47,50,60,62,63 that controlled for GDM, maternal obesity was associated with a 1.2–4.0 higher likelihood of cesarean delivery among obese women vs. normal weight women. Similar findings have been reported for overweight and severely obese women. A meta-analysis64 of 20 studies reported pooled estimates for the likelihood of cesarean delivery by BMI categories. The likelihood of cesarean delivery was 1.46 (95% CI 1.34–1.60), 2.05 (95% CI 1.86–2.27), and 2.89 (95% CI 2.28–3.79) higher, respectively, among overweight, obese, and severely obese women compared with normal weight women (Table 14.2).

Table 14.2

Pooled estimates for cesarean delivery by BMI status from meta-analysis by Chu et al64

Comparison groups

Number of studies

Odds ratio

95% Confidence interval

Overweight vs. normal

23

1.46

1.34–1.60

Obese vs. normal

29

2.05

1.86–2.27

Severely obese vs. normal

7

2.89

2.28–3.79

14.5.4 Preterm Delivery

The relationship of obesity to spontaneous preterm labor and delivery is still being investigated. Multiple investigations have been conducted. Several studies report a small, but positive association; others report no relation between maternal BMI and spontaneous preterm labor. In the Primary Preterm Prevention Study, obese women were less likely to have spontaneous preterm birth than were normal weight women (6.2 vs. 11.2%).65 Conversely, studies do show an association between maternal obesity and indicated preterm birth, particularly in deliveries occurring prior to 32 weeks gestation. In most instances, these deliveries occur in response to hypertension, preeclampsia, or conditions involving poor fetal growth or well-being.

14.5.5 Thrombo-Embolic Events

Pregnancy is a hypercoagulable state. Obesity further increases the risk of thrombosis by promoting venous stasis, increasing blood viscosity and promoting activation of the coagulation cascade. Women are at highest risk at term and there is an increased risk with cesarean delivery.6667 Roberts reported a substantial increase in the odds of deep vein thrombosis (DVT) in overweight and obese women in a prospective study of 14,000 parturients in Nova Scotia even after adjustment for other risk factors. Obese women were 1.9 times more likely to have a DVT (OR 1.9; 1.1–3.9) compared with normal weight women. Severely obese women (BMI ≥40 kg/m2) were 4 times more likely to experience a DVT (OR 4.3; 95% CI 1.2–14.84) relative to normal weight women. Thrombo-embolism is the leading cause of maternal death in pregnancy in developed countries. It is possible that the incidence will increase with increasing maternal obesity. Suggested medical interventions for obese women include the use of pneumatic compression stockings during antenatal hospitalizations as well as labor, cesarean delivery, and postpartum recuperation. Clinicians should encourage ambulation and consider heparin prophylaxis in obese women with prolonged antenatal or postpartum hospitalizations.

14.5.6 Other Maternal Complications

The obese parturient is at risk for several additional complications including wound infection and anesthesia complications. Intubation can be more difficult. The placement of epidural anesthesia can be complicated by difficulty in identifying landmarks. Anatomical distortion can sometimes lead to a higher rate of epidural failure in obese women. Also, because the onset of labor and need for cesarean delivery is unpredictable, obese patients are at increased risk of aspiration due to elevations in gastric residual volume and lower gastric pH.68

Several small studies have examined wound infection in obese women. In a cohort of 239 women, Wall et al69 reported higher rates of infection in obese women (BMI greater than 35 kg/m2) who had a vertical compared to transverse skin incision (34.6 vs. 9.4%). Wolfe and associates70 reported no relation between the type of skin incision and postoperative infection in 107 obese women. Houston and Raynor71 examined the use of the supraumbilical midline skin incision with a fundal uterine incision and breech extraction of the fetus compared with low transverse skin incision. The supraumbilical approach provided less operative time and better wound healing, presumably due to a lesser amount of adipose tissue involved in creating the incision.

Additional studies, ideally prospective and with standard measures of BMI, are needed to provide better data on the incidence of wound infection in women who are overweight or obese. Despite the paucity of large cohort studies, the postoperative morbidity experienced by obese women with wound infection is substantial and greatly influences perinatal cost of care.

14.6 Fetal Complications

14.6.1 Stillbirths

Although there has been a decline in the rate of stillbirths in the United States, stillbirths are not a rare event, with nearly seven stillbirths occurring per 1,000 deliveries (live and stillbirths). Data from the CDC show that there were over 27,000 stillbirths in the year 2000.72 Several epidemiologic studies have reported an increased risk of stillbirth among women who are obese, compared with normal weight women, but the exact mechanism is not completely understood. GDM and hypertensive disease are known risk factors for stillbirths and are more prevalent among obese women. It is also possible that obese women have undiagnosed GDM or some degree of glucose intolerance that adversely affects the developing fetus.

Pre-pregnancy BMI and fetal death were examined in the Danish National Birth Cohort among 54,505 pregnant women. Overweight women had a two times higher risk of stillbirth compared with normal weight women.73Overweight women also experienced a higher risk after 40 weeks gestation (2.9; 95% CI 1.1–7.7). Obese women had a 2.4 times higher risk of stillbirth compared with normal weight women. In a large British study of 325,395 women, overweight and obesity were still associated with fetal death after adjustment for complications of pregnancy (OR 1.1; 95% CI 0.9–1.2) and (OR 1.4; 95% CI 1.1–1.7), respectively.33 Further, Cnattingius et al74 reported an increase in the likelihood of fetal death among obese nulliparous women in Sweden. In a prospective study of over 167,000 women, pregnancies among overweight and obese nulliparous women had a 3.2 (95% CI 1.6–6.2) and 4.3 (95% CI 2.0–9.3) higher odds of fetal death relative to their normal weight counterparts. Among parous women, only obese women had a significant increase in the risk of late fetal death (OR 2.0; 1.2–3.3). Finally, Salihu75 reported that obese mothers were about 40% more likely to experience stillbirth than were nonobese women, after adjustment for demographics and clinical risk factors (HR 1.4; 95% CI 1.3–1.5). Further, there was a dose-dependent relationship between classifications of obesity and stillbirth (P for trend <0.01). For a balanced review, it is important to summarize investigations which reported no association between maternal BMI and stillbirths. Djrolo reported no association between maternal overweight (OR 0.5; 95% 0.15, 1.5) or obesity (0.6; 0.18, 2.0) and stillbirth among a cohort of 323 women. A strength of this study is the use of BMI categories recommended by the World Health Organization (WHO) and Institute of Medicine (IOM), but the analysis is likely limited by sample size and insufficient power, as evidenced by the wide CIs, to detect a meaningful association.

14.6.2 Neural Tube Defects

Neither the presence nor magnitude of association between maternal obesity and neural tube defects (NTDs) has been definitively established. Multiple studies have suggested that maternal obesity without diabetes is associated with an increased risk of delivering an infant with a birth defect,76,77 particularly NTDs.78 Neural tube defects are caused by a failure of neural tube closure 3–4 weeks after conception.79 While the majority of studies have shown an increased risk of NTDs with maternal obesity, other research has shown no association. Also, the magnitude of risk associated with obesity has varied widely, ranging from essentially no risk to a threefold increase in risk. The mechanisms underlying the relation of obesity with NTD are not completely understood. The risk of congenital anomalies is known to be higher among infants of women with diabetes. Therefore, one possible explanation is that obese women have some degree of underlying insulin resistance and higher circulating glucose levels which may also place their infants at risk. Other theories include a reduction in the amount of folic acid that crosses the placenta due to insufficient maternal absorption, chronic hypoxia, and increased circulating levels of triglycerides, uric acid, estrogen, and insulin.76,80

Waller et al80 were the first to report an increased risk of NTDs (both anencephaly and spina bifida) in the offspring of obese women (OR 1.8; 95% CI 1.01–3.19), and especially spina bifida (2.6; 1.5–4.5). Subsequent studies reported similar results.8184 Even after adjustment for ethnicity, maternal age, education, and socioeconomic status, Watkins et al76 reported that each 1 kg/m2 increase in BMI was associated with a 7% increase in the likelihood of having an infant with a NTD. In a recent multi-site, population-based study, Waller et al77 reported adjusted ORs for risk of spina bifida and anencephaly. Obese women had a two times greater risk of spina bifida compared with normal weight women (OR 2.10; 95% 1.62–2.71). There was no increased risk reported in overweight compared with normal weight women.

Little or no association between maternal overweight and NTDs has been reported.80,8587 Hendricks reported an OR of 0.99 (95% CI 0.58, 1.58). Among 499 cases and 534 controls, Waller reported no association (OR 0.92; 95% CI 0.55, 1.55), between maternal overweight status and NTDs. Moore conducted a cohort study of 100 women and found no association between overweight and NTDs. Two studies8488 reported a higher likelihood of NTD (OR 1.91; 95% CI 1.20, 3.04) and (OR 1.61; 95% CI 1.27, 2.05), respectively. A recent meta-analysis89 summarized the findings from 12 (4 cohort and 8 case–control) studies. Using a random effects model, they reported a pooled unadjusted estimate of 1.70 (95% CI 1.34–2.15) for obese women and 1.22 (95% CI 0.99–1.49) for overweight women when compared with normal weight women.

The variability in individual studies of NTDs are due, in part, to differences in study design, including the definitions used for overweight and obesity, variation in the definition of NTDs, and the use of self-reported or measured maternal height and weight. Table 14.3 summarizes the characteristics of several studies included in this review. Only three of the studies used the standard definitions of overweight and obesity recommended by the IOM and the WHO. Five studies80,83,85,88,90 used threshold values for overweight and obesity that were similar to the standard definitions. Three studies used weight alone (in kilograms or pounds) to designate normal, overweight, and obese women.8184,91 While these investigations contribute important, relevant information, the results are somewhat difficult to compare due to heterogeneity in the categorizations of overweight and obesity. Several studies included all types of NTDs, whereas other studies focused on the two most common types of defects, which include anencephaly and spina bifida. Finally, it is possible that some women were misclassified as overweight or obese due to the use of self-reported maternal height and weight. Validity studies suggest that reproductive-age women tend to underestimate weight and overestimate height.92 If so, the association between maternal obesity and NTDs would most likely be underestimated, and therefore, would not substantially modify the results of published studies. Overall, maternal obesity is associated with an increased risk of NTDs, although the absolute increase is likely small.

Table 14.3

Characteristics of select studies of maternal obesity and neural tube defects (NTDs)7679

References

Study design/data sources

Source of maternal weight and height

Definitions

NTDs included

Anderson et al82

Case–control, Birth defects surveillance system

Self-reported

Normal:18.5–24.9 kg/m2

Overweight: 25–29.9 kg/m2

Obese: 30–39.9 kg/m2

Severely obese: ≥40 kg/m2

Anencephaly, spina bifida

Feldman et al91

Retrospective cohort

Retrieved from database

Normal: 100–140 lbs

Overweight: 141–180 lbs

Obese: 181–260 lbs

Severely obese: 261–300 lbs

Did not specify NTDs

Hendricks et al86

Case–control, Birth defects surveillance system

Self-reported

Normal:18.5–24.9 kg/m2

Overweight: 25–29.9 kg/m2

Obese: ≥30 kg/m2

Anencephaly, spina bifida, encephalocele

Kallen90

Retrospective cohort

National birth registry

Normal:19.8–26 kg/m2

Overweight: 26.1–29 kg/m2

Obese: >29 kg/m2

Anencephaly, spina bifida

Mikhail et al, 2005

Case–control, Perinatal database and clinical records

Weight and height abstracted from patient records to derive calculated BMI

Normal: <27 kg/m2

Overweight: ≥27 kg/m2

NTDs

Moore et al85

Prospective cohort from screening women in 100 obstetrical clinics

Measured

Normal: <25 kg/m2

Overweight: 25–27.9 kg/m2

Obese: ≥28 kg/m2

Did not specify type of NTDs

Ray et al81

Retrospective cohort from screening women during antenatal visits and discharge database

Retrieved from database

Normal: 52–64.1 kg

Overweight: 64.2–85.6 kg

Obese: >85.6 kg

Spina bifida, anencephaly

Shaw et al88

Case–control, Birth defects surveillance system

Self-reported

Normal:19–27 kg/m2

Overweight: 28–30 kg/m2

Obese: 31–37 kg/m2

Severely obese: ≥38 kg/m2

Anencephaly, spina bifida cystic, craniorachischisis, iniencephaly

Waller et al80

Case–control, Perinatal database and genetic records

Self-reported

Normal:19–27 kg/m2

Overweight: 28–30 kg/m2

Obese: 31–37 kg/m2

Severely obese: ≥38 kg/m2

Anencephaly, spina bifida, encephalocele

Watkins et al83

Case–control, Birth defects surveillance system

Retrieved from birth certificates

Normal:19.9–26 kg/m2

Overweight: 26.1–29 kg/m2

Obese: >29 kg/m2

Anencephaly, spina bifida

Watkins et al76

Case–control, Birth defects surveillance system

Self-reported

Normal:18.5–24.9 kg/m2

Overweight: 25–29.9 kg/m2

Obese: ≥30 kg/m2

Anencephaly, spina bifida, encephalocele

Werler et al84

Case–control, Surveillance program based on tertiary and birth hospitals

Self-reported

Normal: 50–69 kg

Overweight: 70–89 kg

Obese: 90–109 kg

Severely obese: ≥110 kg

Anencephaly, spina bifida, encephalocele

14.7 Fetal Ultrasound Assessment

Obstetrical ultrasound is a primary tool in the identification of congenital anomalies, such as NTDs and in the evaluation of fetal growth and well-being. Maternal obesity can limit the accuracy of prenatal ultrasound and can therefore increase the likelihood of an undetected fetal structural abnormality. Hendler et al93 reported suboptimal rates of visualization of the fetal cardiac structures by 43% in the babies of obese women. Wolfe and associates94conducted a prospective study of 1,622 ultrasounds performed in the second and third trimesters of pregnancy. The average gestational age at the time of ultrasound was 25 weeks. Each ultrasound was reviewed and classified as visualized or suboptimally visualized. Among women with BMI in the 97th percentile, visualization was decreased to 63%. Visualization of all organ systems was decreased by 14.5% in women with BMI greater than the 90th percentile compared with women with normal BMI.

Several studies have investigated the best portion of the maternal abdomen on which to conduct ultrasound and investigated optimal timing of second trimester anatomical ultrasound. Rosenberg95 conducted a small study assessing ultrasound images through the umbilicus, the thinnest section of the abdominal wall. He reported that 18 of 19 previously incomplete cardiac surveys were possible with the transumbilical approach. Optimal timing for performing second-trimester anatomical scans in obese women is reported to be at 18–20 weeks gestation based on a prospective study by Lantz.96

14.8 Conclusions

Rates of obesity are increasing across populations. Women of childbearing age are among those affected. Maternal obesity can affect not only the health of the mother, but also the well-being of her children.97The underlying cause of this epidemic is multifactorial, including caloric intake, physical activity and potential familial and genetic components. The perinatal period is an important time frame during which to critically address obesity, particularly in the glucose-tolerant parturient who is still at risk for multiple complications, mirroring many of those that occur among glucose-intolerant women. There is a large and consistent body of literature supporting an association between maternal obesity and GDM, hypertensive disorders, cesarean delivery, NTDs, and stillbirths. Further mechanistic studies are necessary to better understand the effect of obesity on development of NTDs and the occurrence of stillbirth. Additional longitudinal studies are needed to further explore the relation of maternal obesity and spontaneous preterm delivery. While there are fewer large multicenter studies on maternal obesity and postoperative complications, multiple single site studies support a higher likelihood of anesthetic, wound, and thrombo-embolic events in this population. Further studies in these areas should focus on the implementation of operative interventions and postoperative care guidelines to reduce the incidence of these complications. Perhaps most importantly, evidence-based interventions to promote appropriate maternal weight in the preconception and interconception periods are paramount in addressing the maternal obesity epidemic and the associated pregnancy complications.

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