Obesity is a rising global epidemic. Obesity during pregnancy is associated with increased maternal and fetal risks, which is inversely correlated with the severity level of obesity. Other comorbidities are common (diabetes mellitus, hypertensive disorders, etc.) and contribute to an even increased risk. Maternal obesity during pregnancy contributes also to offspring obesity and noncommunicable diseases later in life in a vicious cycle. Managing these problems, and potentially reducing their risk, can pose a challenge in obstetric care. It is important to provide preconception nutritional and exercise care, and guidance during pregnancy and post pregnancy for appropriate weight loss.
Obesity – introduction
A noncommunicative disease (NCD) is considered a medical condition, which by definition is noninfectious and non-transmissible among people. The World Health Organization (WHO) reports NCDs to be by far the leading cause of death in the western world .
We believe that obesity in general, and in obstetrics in particular, should be independently considered one of the NCDs. Obesity is often accompanied by other chronic and obstetric diseases; however, it is not always clear whether obesity is the direct cause of adverse pregnancy outcomes by itself or only associated with pregnancy outcome The recent National Health and Nutrition Examination Survey found that more than one-third of reproductive-aged women were obese, and 7.6% of those women were extremely obese (body mass index (BMI) ≥40 kg/m 2 ) .
Definitions
Overweight and obesity are defined as abnormal or excessive percent fat accumulation that may impair health. The WHO and the National Institutes of Health define underweight as a BMI of ≤18.5, normal weight as a BMI of 18.5–24.9, overweight as a BMI of 25–29.9, and obesity as a BMI of ≥30. Obesity is further characterized by BMI into class I (30–34.9), class II (35–39.9), and class III (>40) .
However, BMI by itself is a surrogate marker of adiposity and does not measure adipose tissue directly. As a result, it has limitations and provides no information on fat distribution . As a rule, women have more body fat than men, and it is widely agreed that women with > 25% body fat are obese . Moreover, much of the published research on obesity is based on self-reporting of height and weight which has been shown to be unreliable .
Due to expected weight gain variability during pregnancy and the short interval of time, there is no accepted definition for obesity during pregnancy. It is strongly recommended that in pregnant women, BMI will be calculated at the first antenatal visit in the first trimester, as during pregnancy the BMI is not recalculated. Some of the studies use other measures to define obesity including weight at delivery and the waist to hip ratio (WHR) .
Gestational weight gain is generally lower in obese women compared with normal-weight women irrespective of any interventions . There have also been inconsistencies in the way gestational weight gain is measured . In the United States, gestational weight gain is measured during pregnancy. The US Institute of Medicine (IOM) guidelines , based on observational data , stated that healthy women who are at a normal weight for their height (BMI 18.5–24.9) should gain 11.5–16 kg (25–35 pounds) during pregnancy. As BMI increases, gestational weight gain should be decreased ( Table 1 ).
| Prepregnancy BMI (kg/m 2 ) | Range (kg) | Range (lb) |
|---|---|---|
| Underweight (<18.5) | 12.5–18.0 | 28–40 |
| Normal weight (18.5–24.9) | 11.5–16.0 | 25–35 |
| Overweight (25.0–29.9) | 7.0–11.5 | 15–25 |
| Obese (>29.9) | 5.0–9.0 | 11–20 |
The Society of Obstetricians and Gynecologists of Canada published in 2010 a clinical practice guideline with roughly similar numbers. Overweight and obese women gaining weight within IOM recommendations have less preeclampsia and emergency cesarean sections; however, they continue to be at an increased risk of gestational diabetes, small for gestational age, and preterm and perinatal mortality compared with those who gain less than the IOM recommendations .
Weight gain above the IOM recommendations has been associated with poor maternal and fetal outcomes independent of prepregnancy BMI. By contrast, Britain’s National Institute for Health and Clinical Excellence (NICE) recommends that women should not be weighed repeatedly during pregnancy as a matter of routine and only if weight has a clinical influence or if nutrition is a concern.
Pregnancy is considered a window of opportunity for the promotion of healthy eating and physical activity behavior among women .
Definitions
Overweight and obesity are defined as abnormal or excessive percent fat accumulation that may impair health. The WHO and the National Institutes of Health define underweight as a BMI of ≤18.5, normal weight as a BMI of 18.5–24.9, overweight as a BMI of 25–29.9, and obesity as a BMI of ≥30. Obesity is further characterized by BMI into class I (30–34.9), class II (35–39.9), and class III (>40) .
However, BMI by itself is a surrogate marker of adiposity and does not measure adipose tissue directly. As a result, it has limitations and provides no information on fat distribution . As a rule, women have more body fat than men, and it is widely agreed that women with > 25% body fat are obese . Moreover, much of the published research on obesity is based on self-reporting of height and weight which has been shown to be unreliable .
Due to expected weight gain variability during pregnancy and the short interval of time, there is no accepted definition for obesity during pregnancy. It is strongly recommended that in pregnant women, BMI will be calculated at the first antenatal visit in the first trimester, as during pregnancy the BMI is not recalculated. Some of the studies use other measures to define obesity including weight at delivery and the waist to hip ratio (WHR) .
Gestational weight gain is generally lower in obese women compared with normal-weight women irrespective of any interventions . There have also been inconsistencies in the way gestational weight gain is measured . In the United States, gestational weight gain is measured during pregnancy. The US Institute of Medicine (IOM) guidelines , based on observational data , stated that healthy women who are at a normal weight for their height (BMI 18.5–24.9) should gain 11.5–16 kg (25–35 pounds) during pregnancy. As BMI increases, gestational weight gain should be decreased ( Table 1 ).
| Prepregnancy BMI (kg/m 2 ) | Range (kg) | Range (lb) |
|---|---|---|
| Underweight (<18.5) | 12.5–18.0 | 28–40 |
| Normal weight (18.5–24.9) | 11.5–16.0 | 25–35 |
| Overweight (25.0–29.9) | 7.0–11.5 | 15–25 |
| Obese (>29.9) | 5.0–9.0 | 11–20 |
The Society of Obstetricians and Gynecologists of Canada published in 2010 a clinical practice guideline with roughly similar numbers. Overweight and obese women gaining weight within IOM recommendations have less preeclampsia and emergency cesarean sections; however, they continue to be at an increased risk of gestational diabetes, small for gestational age, and preterm and perinatal mortality compared with those who gain less than the IOM recommendations .
Weight gain above the IOM recommendations has been associated with poor maternal and fetal outcomes independent of prepregnancy BMI. By contrast, Britain’s National Institute for Health and Clinical Excellence (NICE) recommends that women should not be weighed repeatedly during pregnancy as a matter of routine and only if weight has a clinical influence or if nutrition is a concern.
Pregnancy is considered a window of opportunity for the promotion of healthy eating and physical activity behavior among women .
Scope of the problem
The latest reports of the WHO indicate that in 2008 approximately 1.4 billion adults were overweight. Of these overweight adults, over 200 million men and nearly 300 million women were obese. The WHO also projects that, by 2015, approximately 2.3 billion adults will be overweight and >700 million will be obese .
Human pregnancy is an insulin-resistant condition by itself, potentially compounded by increased pregravid insulin resistance in obese women. There is a 40–50% increase in insulin resistance during pregnancy (from the pregravid condition) .
International guidelines
Worldwide, international committees addressed the issue of obesity in pregnancy and advise an oriented weight surveillance approach .
The American College of Obstetricians and Gynecologists (ACOG), in their committee opinion , strongly encourage preconception assessment and counseling for obese women that should include the provision of specific information concerning the maternal and fetal risks of obesity in pregnancy, as well as encouragement to undertake a weight-reduction program including diet, exercise, and behavior modification. At the initial prenatal visit, height and weight should be recorded for all women to allow calculation of BMI, and recommendations for appropriate weight gain, guided by IOM recommendations, should be reviewed both at the initial visit and periodically throughout pregnancy.
The Royal College of Obstetricians and Gynecologists (RCOG), in a joint guideline with the Centre for Maternal and Child Enquiries (CMACE) , addressed the issues above and emphasized that the management of women with obesity in pregnancy should be integrated into all antenatal clinics, with available clear policies and guidelines for care. The guideline also reinforced the need for dietary supplements (folic acid and vitamin D) during pregnancy. Special attention was particularly given to the subclass of morbidly obese parturitions (BMI ≥ 40) and a comprehensive approach was suggested that included an antenatal consultation with an obstetric anesthetist and a documented assessment in the third trimester of pregnancy to determine manual handling requirements for childbirth and consider tissue viability issues.
The UK NICE also published guidance in 2010 regarding weight management before, during, and after pregnancy . The guidance recommends which actions should be taken in the obese population in preparing for pregnancy, during pregnancy, and after childbirth with respect to nutrition and physical activity.
The Society of Obstetricians and Gynaecologists of Canada published in 2010a clinical practice about obesity in pregnancy dealing with the issues above and also focused on the preconception period and the opportunity for the gynecologist to raise the issue of weight loss.
The Royal College of Physicians in Ireland and the Royal Australian and New Zealand College of Obstetricians and Gynaecologists also published local guidelines dealing with obesity in pregnancy .
Obstetrical management of the obese gravida
It is now universally acknowledged that maternal overweight and obesity are linked with adverse pregnancy outcome. There are known higher infertility rates, maternal complications including hypertension, diabetes, respiratory complications, (asthma and sleep apnea), thromboembolic disease, more frequent intrapartum complications and cesarean delivery with increased wound infection, endometritis, and anesthetic complications (mainly difficulties in intubation and placement of regional anesthesia). Newborn complications include congenital malformations, large-for-gestational-age infants, shoulder dystocia, and long-term adolescent complications (obesity, diabetes, and possibly more). Class II and III obese women are prone to an even increased rate of complications and adverse outcomes.
Prepregnancy consultation
Weight reduction
It is well established that the best management for obesity is prevention. Usually, by the time of pregnancy diagnosis in the obese patient, the impaired organogenesis may have already occurred . Thus, the ideal time for intervention is before conception and the primary care services should ensure that all women of childbearing age have consultation on how to optimize their weight prior to pregnancy. Interventions include behavioral modification, dietary changes, exercise, pharmacotherapy, and surgical intervention of bariatric surgery . Inter-pregnancy weight reduction among women with obesity has been shown to significantly reduce the risk of developing GDM . An increase in pregravid weight between the first and second pregnancies resulted in an increased risk of preeclampsia (odds ratio (OR), 3.2; 95% confidence interval (CI), 2.5–4.2), whereas a decrease in pregravid weight between the first and second pregnancies from obese to a normal BMI decreased the risk of cesarean delivery and large-for-gestational-age infants .
Consultation regarding risks and outcomes of obesity
Women with a BMI ≥30 should receive information and advice about the risks of obesity during pregnancy and childbirth, and they should be advised about the possible strategies to minimize them prior to conception. Several studies have shown an increased risk of anovulatory infertility in obese women (OR = 2–3) by mechanisms including hyperandrogenism and polycystic ovary syndrome (PCOS), which share several pathophysiological characteristics, namely insulin resistance . Body fat distribution in women of reproductive age seems to have more impact on fertility than age or obesity itself; a 0.1-unit increase in waist–hip ratio led to a 30% decrease in probability of conception per cycle (hazards ratio (HR) 0.7; 95% CI 0.5–0.8) . If an in vitro fertilization (IVF) treatment is needed, the patient should be aware of the possible association of obesity with decreased chances of pregnancy (insufficient follicular development, lower oocyte counts, poor oocyte quality, endometrial quality, or a combination of these factors) . In a systematic review and meta-analysis including 33 studies and almost 48,000 IVF/intra-cytoplasmatic sperm injection (ICSI) treatment cycles, women who were overweight or obese (BMI ≥ 25 kg/m 2 ) had a statistically significant small reduction in clinical pregnancy rate (relative risk (RR) = 0.90) and live-birth rate (RR = 0.84) and a significantly higher miscarriage rate (RR = 1.31) than normal-weight women (BMI < 25 kg/m 2 ) . Some reports found that the outcomes were comparable to nonobese women but needed higher doses of ovulation-inducing agents .
Nutritional and exercise recommendations
Nutrition consultation should be offered to all obese women, and they should be encouraged to follow an exercise program . The ACOG suggests a healthy diet that uses caloric restriction in combination with daily aerobic exercise . Nutritional recommendations include a diet that is high in fiber with fresh fruits, vegetables, lean protein, and complex carbohydrates while avoiding foods that contain large amounts of sugar, saturated fats, and cholesterol. Few guidelines even advise taking 5 mg of folic acid due to the higher risk of NTD in this population and evidence of lower serum folate levels even after controlling for folate intake. Regular aerobic exercises such as brisk walking, stair climbing, jogging, or swimming that use the larger skeletal muscles should be incorporated into weight reduction programs.
There is also increasing evidence regarding the need for vitamin D supplementation during pregnancy, especially in the obese women, as serum vitamin D levels are decreased in this population. Cord serum vitamin D levels in neonates of obese women have also been found to be lower than in babies born to nonobese women .
Antenatal management
Care in the first trimester
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First antenatal visit – The goal of the first meeting is to learn the “medical baseline” of the patient and to assess her level of risk for adverse maternal and perinatal outcomes. Moreover, it is important to set goals for surveillance during pregnancy and to give information and recommendations on how to minimize the risks. Special attention should be given to detailed and thorough history and complete physical examination. It is important to measure the patient’s height and weight as this will serve the physician to calculate the BMI. Questions should be oriented to the higher-risk coexisting medical conditions. As the severity of obesity increases, these are more prevalent and need closer monitoring. For pregnant women at the highest risk of comorbidities (class III obesity), additional tests should be considered as a baseline: laboratory tests (baseline chemistry and 24-h urine collection) as well as maternal echocardiography . Sleep disorder evaluation should be considered in symptomatic patients as obesity is a strong risk factor for obstructive sleep apnea (OSA) which is associated with a higher incidence of maternal (hypertension, stroke, and cardiac dysfunction) and obstetric (hypertension disorders, GDM, and fetal growth retardation) complications. Obese patients should receive dietary counseling to guide them through the pregnancy with documented weight gain goals.
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Miscarriages – Patients should be aware of an increased risk of first-trimester miscarriage, though data are not conclusive. Whereas several studies suggest that obesity may increase the risk of miscarriage due to adverse influences on the embryo, the endometrium, or both , others found no association between miscarriage and obesity . These studies lack consistency, however, mainly because of the use of different obesity classification systems that disregard the WHO criteria.
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Early screening for diabetes – Because obesity is accompanied by insulin resistance that is expected to increase during pregnancy, the obstetrician should consider an early screening for preexisting diabetes mellitus. Women with severe obesity, personal history of gestational diabetes mellitus (GDM) or delivery of large-for-gestational-age infant, glycosuria, PCOS, or a strong family history of diabetes should be given a higher degree of suspicion. A positive first-trimester diagnosis, especially with a high value of glycosylated hemoglobin, is considered pregestational in nature and requires intensive surveillance and treatment . If initially normal, a repeated early third-trimester screening is obligatory.
Care in the second and third trimester
Care in the second and third trimester should be aimed at early identification of fetal, maternal, and placental pathologies. Additional goals of mid-trimester management include ongoing counseling regarding appropriate weight gain and dietary recommendations and maintenance and improvement of coexisting medical disorders.
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Diagnosis of congenital anomalies – Some malformations are found to be in higher prevalence in the obese population and the risk may increase with increasing maternal weight . The malformations that are mostly connected with obesity are neural tube defects and cardiac malformations, though additional malformations are being associated with obesity such as diaphragmatic hernia, hydrocephaly, hypospadias, cystic kidney, omphalocele, and more . Because these types of congenital anomalies are often seen with pregestational diabetes, some investigators suggest that many of these obese women may have had undiagnosed type 2 diabetes . Apart from the increased prevalence of malformations, there is also an increased risk of failure to detect these malformations due to suboptimal visualization of fetal anatomy by ultrasound examination. Approximately 15% of normally visible structures will be suboptimally seen in women with a BMI above the 90th percentile .
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Gestational diabetes mellitus – Several studies demonstrated a two-to tenfold increase in the rate of GDM among obese patients . The magnitude of this risk is positively correlated with increases in maternal weight . Post partum, glucose intolerance associated with GDM generally resolves. However, obese women with a history of GDM have a twofold increased prevalence of subsequent type 2 diabetes compared to lean women . For those women whose first-trimester screening test for GDM was normal, a repeat screening test between 24 and 28 weeks with a 50-g 1-h oral glucose challenge is indicated . As for later screening, though few studies offered some advantages , there is no current evidence to support a significant clinical benefit.
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Pregnancy-associated hypertension – Obese women should be followed up closely for the development of hypertensive disorders, and patients with chronic hypertension should be followed up for the development of superimposed preeclampsia. Hypertensive disorders during pregnancy have been consistently reported to be associated with obesity . A systematic review of 13 cohort studies comprising nearly 1/4 million women showed that the risk of preeclampsia doubled with each 5–7 kg/m 2 increase in prepregnancy BMI. This relation persisted in studies that excluded women with chronic hypertension, diabetes mellitus, or multiple gestations, and other confounders . The mechanism for the association between obesity and preeclampsia is not clear and perhaps related to pathophysiologic changes such as insulin resistance, hyperlipidemia, and subclinical inflammation . Epidemiological studies have reported a relationship between pregnancies complicated by preeclampsia and an increased risk of maternal coronary heart disease in later life .
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Intrauterine fetal death – Obese pregnant women have been shown to have an increased risk of intrauterine fetal death . A meta-analysis including nine controlled studies showed that overweight and obese pregnant women experienced significantly more stillbirths than normal-weight women (OR = 1.5–2), even after controlling for other coexisting complications . The risk of stillbirth increased in a dose-dependent fashion with increase in BMI . A meta-analysis found that maternal overweight and obesity are the highest-ranking modifiable risk factor for stillbirth in high-income populations, with a population-attributable risk of 8–18% . Maternal obesity is also associated with an increased overall risk of infant death, mainly neonatal death .
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Fetal overgrowth – Obesity is a significant and independent contributor impacting fetal growth . Even after adjustment for GDM, there is approximately a twofold RR for macrosomia . Other coexisting diseases can restrict fetal growth . Because body habitus in this population may limit the use of clinical fetal weight estimation, serial ultrasound fetal weight estimation is recommended, especially near term when the decision on the mode of delivery is impending.
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Timing of delivery – Obesity carries a higher risk of preterm delivery. Evidence suggests that obesity may be associated with induced preterm delivery, but not spontaneous preterm birth . Studies show that as the BMI increases, the risk of spontaneous preterm labor decreases whereas the risk of requiring an elective preterm delivery increased . Most studies attribute the risk of induced preterm delivery to obesity-related medical and obstetrical complications (diabetes mellitus, hypertension, and preeclampsia). A recent population-based cohort study that included >1.5 million singleton deliveries observed a dose-dependent relationship between severity of obesity and the risk of spontaneous extremely preterm deliveries (22–27 weeks of gestation) after adjustment of confounders. Inflammatory upregulation mechanisms might be involved . On the other hand, post-term deliveries are also more common in an unknown mechanism. A few of the hypothesized explanations include miscalculation of gestational age or hormonal changes associated with obesity .
Labor, delivery, and post partum
Obesity can create significant challenges of intrapartum care due to difficulties in examination and assessment of the mother and fetus. Additionally, obesity complicates the management of labor by a proven association with macrosomia, shoulder dystocia, cephalopelvic disproportion, and high incidence of operative delivery. Furthermore, morbidly obese women also required more intervention, intense monitoring, and skilled clinical staff in their intrapartum care. Obstetric units that care for extremely obese patients should also have specialized equipment in the delivery room.
Induction of labor
Obese women are more likely than normal-weight women to have an induction of labor because of both an increased rate of obstetrical complications and a prolonged pregnancy in an apparent dose-dependent manner with increasing class of obesity. The magnitude of this risk ranges from a 1.6- to 2.2-fold increase . Induction of labor in the obese patient, compared with the lean patient, is associated with longer induction to delivery time with prostaglandins, higher requirements of oxytocin , and higher chances of failure and subsequent cesarean section (CS) . Common indications for induction failure and CS are fetal distress and arrested labor .
Protracted labor
Observational studies on the progress of labor in the obese parturient have shown different patterns of progress. Obese women are more likely to have an inadequate contraction pattern during the first stage of labor and subsequently have a longer first stage . The exact mechanism of dysfunctional labor in obese women is not completely understood. Several authors have speculated that this dysfunction results from the added soft-tissue deposits in the pelvis of the obese gravid . Another explanation may be related to a greater volume of distribution for ripening agents during the course of labor, making them less effective. Increased levels of leptin, cholesterol, and apelin can also theoretically inhibit uterine muscle contractility . All these factors may contribute to increased rates of labor induction, dysfunctional labor requiring intrapartum cesarean delivery, and postpartum hemorrhage. The duration of the second stage of labor does not appear to be affected by an increase in BMI .
Macrosomia and shoulder dystocia
Maternal prepregnancy weight and decreased prepregnancy insulin sensitivity have been shown to strongly correlate with fetal growth, especially on fetal fat mass accumulation and distribution at birth . Obese women, even in the presence of normal glucose tolerance, are almost twice as likely to have a macrosomic infant . Clearly, this observed increase in birth weight and macrosomia in this group can result in cephalopelvic disproportion, shoulder dystocia and associated inherent birth trauma, perineal lacerations, fetal injury, and postpartum hemorrhage. A study examining maternal anthropometric parameters found that obesity is one of the strongest risk factors (2.7-fold risk) for shoulder dystocia, even after adjustment for confounding factors such as macrosomia and diabetes .
Operative delivery
Obesity is associated with an increased risk of operative vaginal delivery (OVD), probably in a dose-dependent matter . OR may be up to 1.7 for OVD for women with class III obesity in comparison to normal BMI patients . Furthermore, not only does the obese gravida carry a higher risk of operative delivery but also she is prone to fail when trying to. In a population-based database of 60,167 deliveries, the OR for failed operative delivery was 1.75 in women of BMI ≥30 compared with women with BMI <30 . The decision on an attempt of operative delivery in obese patients should be carefully considered.
Cesarean section
The incidence of cesarean delivery correlates with increased prepregnancy BMI and also with excessive gestational weight gain . For women without other complications, the estimated adjusted RR is estimated to be 1.2–1.5 for overweight and obese women and up to 3.1 for morbidly obese women . This risk is further increased by other obesity-related pregnancy complications . Unfortunately, obese women undergoing CS experience more complications, including blood loss, increased operative time, and the need for vertical skin incision . After CS, the obese pregnant patient faces a higher risk of wound infection and endometritis. Perioperative antibiotic prophylaxis to protect against endometritis and surgical site infection may not be as effective in obese patients in the accepted dose, due to different pharmacokinetics and pharmacodynamics , and should be adjusted. An attempt to decrease the incidence of wound breakdown in the obese patients after CS includes closure of the subcutaneous layer . The placement of a subcutaneous drain was not proven to be effective .
Vaginal birth after cesarean section
The impact of morbid obesity on mode of delivery, particularly in those with a previous cesarean, has only been examined in small populations and with disparate results, suggesting a significantly lower success rate of trial of labor after cesarean delivery (TOLAC) . Additionally, normal BMI women who became overweight before the second pregnancy had also decreased vaginal birth after cesarean section (VBAC) rates . In a prospective multicenter study that included >4000 TOLAC attempts, the likelihood of VBAC was related inversely to BMI. Normal-weight women had a VBAC failure rate of 15%, compared with 39% for the morbidly obese (BMI > 40 kg/m 2 ) group. A higher rate of uterine scar dehiscence or rupture was noted for the morbidly obese group (2.1%), compared with the overweight (1.4%) and normal-weight (0.9%) groups. Composite morbidity and neonatal injury rates were found to be greater with increasing BMI .
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