Prepregnancy weight category
BMI (kg/m2)
Recommended weight gain (pounds)
Mean (range) in pounds/week in second and third trimestera
Recommended weight gain for twin gestation (pounds)
Underweight
<18.5
28–40
1 (1–3)
No recommendations
Normal weight
18.5–24.9
25–35
1 (0.8–1)
37–54
Overweight
25–29.9
15–25
0.6 (0.5–0.7)
31–50
Obese
≥30
11–20
0.5 (0.4–0.6)
25–42
Comorbidities in Pregnancy
Although obesity by itself can be considered a comorbidity in pregnancy, many medical conditions that are common in obese women often complicate pregnancy. These include hypertension, diabetes, hyperlipidemia, obstructive sleep apnea (OSA), and history of bariatric surgery.
Chronic Hypertension
Chronic hypertension is present in up to 5 % of all pregnant women, and is much more common in obese women [14, 15]. Chronic hypertension can cause end-organ damage, thereby complicating pregnancy even further by causing cardiomegaly, ischemic heart disease, left ventricular hypertrophy, renal involvement, or retinopathy [16]. Additionally, chronic hypertension increases the maternal risks of overall mortality, preeclampsia, cesarean delivery, and placental abruption, and the fetal risks of growth restriction and fetal demise [17–19].
Pregestational Diabetes
Pregestational diabetes is present in 1 % of all pregnancies and is associated with significant morbidity in pregnancy [20]. As with chronic hypertension, women with pregestational diabetes may have significant involvement of the cardiac and renal systems. Risks that are increased by pregestational diabetes include preeclampsia, cesarean delivery, preterm delivery (PTD), spontaneous abortion (SAB), fetal demise, fetal growth abnormality, congenital anomalies, and neonatal complications [21–23].
Hyperlipidemia
Obstructive Sleep Apnea
OSA, an underdiagnosed but common comorbidity of obesity in pregnancy, is also a known secondary cause of hypertension, cardiovascular disease, and mood disturbances [26, 27]. OSA has been associated with fetal growth restriction, preeclampsia, and stillbirth [28]. However, one of the greatest considerations in obese women with sleep apnea is difficulty with anesthesia administration, especially when general anesthesia is required.
Bariatric Surgery
With the high rate of obesity, an increasing number of reproductive-age women are undergoing bariatric surgery [29]. Several studies have concluded that rates of many adverse maternal and neonatal outcomes are lower in women who become pregnant after bariatric surgery than in obese women who have not had bariatric surgery [30]. Nonetheless, there are some considerations for pregnant women with prior bariatric surgery. For instance, prior abdominal surgery can increase the risks incurred during a cesarean delivery, vitamin deficiencies can be a concern, especially in malabsorptive types of surgery, and testing for gestational diabetes may need to be altered because of rapid gastric emptying (or dumping syndrome) [31].
Maternal Complications and Risks
Pregnancy-associated maternal morbidities have consistently been shown to be higher among obese women than normal-weight women at all stages of pregnancy. Antepartum risks include gestational diabetes, gestational hypertension, and preeclampsia. Intrapartum complications include induction and cesarean delivery. Finally, postpartum complications such as venous thromboembolism and wound complication are increased in obese women.
Gestational Hypertension and Preeclampsia
Gestational hypertension complicates pregnancy in 4.8 % of normal-weight women and 10.2 % of obese women, thus putting obese women at increased risk of preeclampsia [32]. For example, a systematic review by Obrien et al. found that the risk of preeclampsia doubled for every 5–7 kg/m2 increase in prepregnancy BMI [33]. Additionally, Bodnar et al. found that obese women were at threefold higher risk for preeclampsia than normal-weight women [34].
Gestational Diabetes
Prepregnancy BMI is a strong predictor in the development of gestational diabetes [35]. Torloni et al. reported that moderately obese (Class I and II) and morbidly obese (Class III) women have three- and over fivefold, respectively, higher risk of developing gestational diabetes than normal-weight women [36]. Furthermore, a recent meta-analysis reported that severely obese women (Class II and III) have an increased risk (OR 8.6) of gestational diabetes [37].
Induction of Labor and Cesarean Delivery
Obesity has been found to be an independent risk factor for induction of labor and cesarean delivery [38, 39]. For example, a retrospective cohort study by Kominiarek et al. reported that the risk for cesarean increased by 2–5 % for every 1 kg/m2 rise in BMI [39], and several studies have demonstrated that obese women are at increased risk of cesarean regardless of parity or prior cesarean history [40]. Some studies have shown that obese women are at increased risk of cesarean during the first, but not the second stage of labor [41]. This may be due to differences in the labor curve in obese women, which will be discussed later in this chapter.
Venous Thromboembolism
The rate of hospitalization for pregnancy-associated venous thromboembolism has increased along with the rate of obesity. Ghaji et al. found that from 1994 to 2009, there was a 14 % increase in the total rate of venous thromboembolism; rates increased by 17 % and 47 % in the antepartum and postpartum periods, respectively. In the same time frame, the prevalence of obesity among pregnant women hospitalized for pregnancy-associated venous thromboembolism doubled [42].
Wound Complication
Obese women are at higher risk for wound complications after cesarean delivery, including separation and infection, than normal-weight women. Rates of such complications range from 3.5 to 30 % [43–47]. Additionally, a dose–response relationship exists between BMI and risk of post-cesarean wound complications [48] (Fig. 8.1).
Fig. 8.1
Incidence of wound complication related to increasing BMI. Figure from: Conner SN, Verticchio JC, Tuuli MG, Odibo AO, Macones GA, Cahill AG. Maternal Obesity and Risk of Postcesarean Wound Complications. American Journal of Perinatology. 2013 Jun 13
Fetal and Obstetric Complications
Possible obstetric complications of maternal obesity include SAB and PTD. The fetal risks include macrosomia, stillbirth, and congenital anomalies.
Spontaneous Abortion
Several studies have observed an association between high BMI and risk of SAB. For example, a meta-analysis performed by Boots et al., which included a pooled cohort of over 28,000 women with spontaneous conception, found higher rates of SAB in obese women than normal-weight women (13.6 % vs. 10.7 %, OR 1.31, 95 % CI 1.18–1.46) [49]. Metwally et al. included overweight women in their meta-analysis and found that the OR for SAB in women with BMI > 25 was 1.67 (95 % CI 1.25–2.25) [50]. Investigations into SAB rate in obese women after confirmed fetal heart activity reveal conflicting findings; some studies suggested an increased risk of SAB, whereas others showed no difference [51, 52]. Additionally, there is evidence that obese women undergoing infertility treatments have increased SAB rates [53, 54].
Preterm Delivery
The association between obesity and risk for PTD has not been well delineated. Rates of indicated PTD are clearly elevated among obese women because of comorbid conditions and increased rates of maternal, fetal, and obstetric complications, but the relationship between obesity and spontaneous PTD is not clear. Reviews have consistently shown that women in higher obesity classes (II and III) have increased risks for PTD, but risk estimates for women in obesity Class I are less consistent [55, 56]. A recent population-based retrospective cohort study of over 1.5 million deliveries found an overall increased risk for PTD in obese women and observed a dose response for higher BMI classes. However, when investigating the risk for spontaneous PTD, only extreme PTD (22–27 weeks’ gestation) was found to be elevated in women with BMI ≥ 30 [57]. More data are needed to determine the risk of spontaneous PTD in obese women.
Macrosomia
Diabetes is a well-known risk factor for macrosomia (birth weight >4,500 g), but obesity alone has also been shown to be an independent risk factor for fetal macrosomia. A retrospective cohort study of over 12,000 deliveries found that, compared to subjects with normal BMI, obese women were at higher risk for birth weight in the 90th percentile or greater (16.8 % vs. 10.5 %) [58]. Furthermore, a recent meta-analysis found that obese women have over threefold higher risk for macrosomia than women with normal BMI (OR 3.23, 95 % CI 2.39–4.37) [59].
Stillbirth
Congenital Anomalies
Several investigations have shown an association between maternal obesity and increased risk of specific congenital anomalies. Obese women are at the highest risk for fetuses with neural tube defects, hydrocephaly, and cardiac defects [64–67] (see Table 8.3). Compounding this finding, limitations in ultrasound because of body habitus can make diagnosis of fetal anomalies difficult in women with high BMI.
Table 8.3
Obesity and risk of specific congenital anomalies
|
Anomaly |
Stothard et al. |
Watkins et al. |
Waller et al. |
Shaw et al. |
|---|---|---|---|---|
|
Meta-analysis |
Case control |
Case control |
Case control | |
|
NTD/spina bifida |
1.87 (1.62–2.15) |
3.50 (1.20–10.30) |
2.19 (1.69–2.85) |
1.90 (1.30–2.90) |
|
Hydrocephaly |
1.68 (1.19–2.36) |
– |
1.27 (0.74–2.19) |
– |
|
Cardiac |
1.30 (1.12–1.51) |
2.00 (1.20–3.40) |
1.33 (1.17–1.52) |
– |
|
Cleft lip and palate |
1.20 (1.03–1.40) |
– |
1.07 (0.86–1.32) |
– |
|
Gastroschisis |
0.17 (0.10–0.30) |
– |
0.19 (0.10–0.35) |
– |
Pregnancy Management Guidelines
Given the prevalence of obesity encountered in general obstetric practice, it is important to have an evidence-based approach to antepartum, intrapartum, and postpartum management to minimize morbidity in these patients. It is important to note, however, that patients are individuals with differing comorbidities, and their care should not be determined solely on the basis of BMI.
Initial Counseling
All initial prenatal visits for obese pregnant patients should include counseling regarding nutrition, weight gain, and anticipated risks to the pregnancy. Women should be informed of the recommendations about daily caloric intake, daily amounts of each food group for each trimester, and key vitamins and minerals required during pregnancy. This can be accomplished by providing patients with the education pamphlet from ACOG on nutrition during pregnancy or referring patients to a registered dietician for additional counseling. Obese pregnant patients should be counseled regarding optimal weight gain, as discussed previously in this chapter [11]. In addition, the initial counseling session should highlight maternal, fetal, and obstetric risks associated with obesity, and attention should be paid to portray accurate risk estimates.
Early Anatomy Scan
Most pregnant women undergo a routine anatomic survey to detect fetal anomalies during the second trimester, between 18 and 22 weeks’ gestation [68]. Although obese women are at higher risk for fetal congenital anomalies, multiple large retrospective cohort studies have shown that the odds of detection of fetal anomalies are significantly decreased in obese women [69–71]. For example, Thornburg et al. found that whereas completion rates for a standard anatomic survey were 79 % for normal-weight women, they were 72 %, 61 %, and 49 % for women with Class I, Class II, and Class III obesity, respectively [71]. Another study reported that 66 % of fetal anomalies were detected with standard ultrasound examination in normal-weight women, but 25–48 % of such anomalies were detected in obese women [70]. Based on these findings, first-trimester ultrasound is emerging as an additional screening tool for detection of severe fetal anomalies in morbidly obese women. First-trimester evaluation of limited fetal anatomy can be performed transvaginally, thus avoiding the abdominal pannus. However, further research is needed to assess the benefit of first-trimester ultrasound for fetal anatomy screening in obese women.
Early Screening for Gestational Diabetes
Because maternal obesity increases the risks for gestational and pregestational diabetes, early screening can improve fetal outcomes. Performing a one-hour glucose challenge test as early as the first prenatal visit in women with BMI ≥ 30 can effectively identify women with undiagnosed type 2 diabetes [72, 73]. When early screening is negative, repeat screening should be implemented between 24 and 28 weeks’ gestation.
Aneuploidy Screening
First and second trimester screening for aneuploidy should be routinely offered to all pregnant women [74]. Evidence suggests that high BMI is not associated with suboptimal visualization on first-trimester nuchal translucency measurement, but there is a higher likelihood that transvaginal views will be required to complete the assessment [75]. Additionally, there are no data to suggest that maternal serum screening accuracy is affected by maternal weight. Therefore, counseling on genetic screening options should be identical for obese and normal-weight women.
Monitoring Fetal Growth
Obese women are at increased risk for macrosomia and large-for-gestational-age infants [76, 77], but because of maternal habitus in obese patients, clinical sizing by Leopold maneuvers and fundal height measurements can often be misleading and overestimate fetal size. This problem is often obviated because many obese patients will have other comorbidities, such as diabetes or chronic hypertension, that act as indications for serial fetal growth assessment via ultrasound. For obese women with no indications for serial assessments of fetal growth, there is a paucity of evidence on the best method of screening for fetal growth abnormalities. It is reasonable to attempt clinical sizing based on maternal body habitus, and then obtain ultrasound measurements if fetal growth abnormality is suspected. Further research is required on this subject.
Antenatal Testing
Women with BMI ≥ 30 have increased rates of stillbirth independent from obesity-related comorbidities [61, 76, 78]. Antepartum fetal surveillance through the use of non-stress tests and biophysical profiles are currently implemented for a variety of other maternal and fetal indications in order to reduce the risk of stillbirth. In 2009, Signore recommended that the role of antenatal testing in obesity should be a focus of future research [79]. Currently, convincing data on the benefit of routine antenatal fetal surveillance solely for the indication of maternal obesity is lacking. Given the technical difficulties of performing fetal testing in obese pregnant women, the false-positive rate of non-reassuring testing must be investigated before fetal testing is routinely employed in obese women who lack additional comorbidities.
Delivery Planning
Anesthesia Management
The physiologic effects of pregnancy increase the difficulty of anesthesia administration, and increasing BMI can compound these technical challenges. For example, intubation for initiation of general anesthesia in emergent cesarean deliveries is more difficult in obese women than in normal-weight women and is of primary concern. Therefore, early placement of regional anesthesia has been advocated as a strategy to reduce the need for general anesthesia in emergent situations. Another concern was illustrated by a prospective cohort study by Bamgbade et al., which found that obesity was associated with increased difficulty in performing regional anesthesia. Although more than two attempts were required for successful placement, failure rates were not increased in obese women [80]. In addition to difficult placement, obese women have been found to have more frequent persistent hypotension and fetal heart rate decelerations after epidural anesthesia [81]. Overall, in the anesthetic management of obese patients in labor, communication between obstetricians and anesthesiologists should be initiated early and often.
Induction of Labor
Because of higher rates of maternal and fetal complications in pregnancy, obese women are at increased risk for indicated induction of labor. Obese women are also more likely than normal-weight women to have a failed induction and undergo cesarean delivery. Wolfe et al. reported that the likelihood of a failed induction increased with increasing obesity class: 13 %, 20.2 %, 24.2 %, and 29 % for normal weight, obesity Class I, Class II, and Class III, respectively [82]. Furthermore, in a secondary analysis of a randomized controlled trial of women induced with prostaglandins, Pevzner et al. found that the duration of labor, oxytocin requirements, and cesarean delivery rates were significantly higher as the degree of obesity increased [83]. Therefore, it is prudent to weigh the risks and benefits of induction of labor in obese patients, especially in the case of elective induction.
Trial of Labor After Cesarean
Obesity has consistently been cited as a risk factor for failed trial of labor after cesarean, with failure rates increasing with increasing BMI [84, 85]. In a multicenter prospective cohort study of 14,529 women undergoing trial of labor after cesarean, the success rate for obese women was 68.4 %, whereas 79.6 % of nonobese women were successful [86]. Additionally, in a secondary analysis investigating maternal and neonatal morbidities from trial of labor, morbidly obese women were found to have a fivefold higher risk of uterine rupture or dehiscence than normal-weight women (2.1 % vs. 0.4 %) [87]. The etiology for decreased success rates in obese patients is unknown, but it is possible that physicians wish to avoid the morbidity associated with an emergent cesarean and thus have a lower threshold for advising a cesarean delivery. Another hypothesis is that obese women are more likely to fail trial of labor because their labor curve progression is different from their nonobese counterparts, thus leading to an increased likelihood of cesarean for labor arrest. Obese patients considering trial of labor after cesarean should be aware of the lower success rates but also consider their increased risk of morbidities incurred with cesarean delivery.
Labor Management: Changes to the Labor Curve
It is important to recognize that increasing BMI is associated with slower labor progression in both nulliparous and multiparous women [88]. A recent retrospective cohort study among 5,204 consecutive singleton term pregnancies who completed the first stage of labor found that the overall duration of labor was longer, and progression of the early part of the first stage was slower, in obese women than in normal-weight women [89]. These findings should be considered before performing a cesarean for labor arrest in an obese patient (Fig. 8.2). However, there is no association between BMI and length of the second stage or risk for cesarean [90].
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