16 Mary Higgins and Fionnuala McAuliffe UCD Perinatal Research Centre, University College Dublin, National Maternity Hospital, Dublin, Ireland Rates of women with a body mass index (BMI) greater than 30 of reproductive age are rising, with recent estimates of over 25% common in many countries. Therefore obesity in pregnancy is a significant health issue. Obstetricians, when meeting an obese woman in early pregnancy, often focus on the short‐term complications of obesity in pregnancy, such as the risk of gestational diabetes mellitus (GDM), pre‐eclampsia and thromboembolism, the difficulty of fetal assessment, using ultrasound and fetal heart rate (FHR) monitoring, and the risks of labour. These complications often increase with increasing BMI in a dose–response fashion. Complications need to be considered seriously, as the potential problems may not be minor: obesity has been shown to increase the risk of morbidity and mortality [1]. While the immediate risks may be evident to any clinician in practice, what may not be appreciated are the subtle risks of obesity in pregnancy, how even mild obesity may affect progress in labour, the relative malnutrition of vitamins and minerals, maternal malabsorption and consequent malnutrition as a result of bariatric surgery, as well as the effects of maternal obesity on both fetal programming and long‐term risk of cardiovascular disease and the increased risk of childhood obesity. In addition, though many appreciate the risks of morbid obesity (BMI >40, class 3 obesity; Table 16.1) on pregnancy, the clinical team may not fully appreciate the risks of even ‘mild’ obesity on pregnancy and the effect of pregnancy on the associated complications of obesity. Adipose tissue is an endocrine organ, synthesizing and secreting a variety of hormones and inflammatory markers, including cytokines, leptin and adiponectin. These adipocytokines can have profound effects on pregnancy. Table 16.1 Classification of maternal BMI (kg/m2) and cut‐off points for defining maternal obesity. It is well recognized that obesity is increasing in prevalence in both the developed and developing world. Increased sedentary lifestyles, changes in diet and nutrition and a reluctance to implement large‐scale public health policies to challenge obesity [2] have resulted in a population very different to that of the 1950s when Friedman first described the ‘normal’ progress of labour, now known as the Friedman curve [3]. Then, as now, the average BMI of women in labour corresponded to the average BMI of those times, but in the 1950s the median BMI range was 20. Friedman’s curve may not apply to the obese, or even overweight, woman. While all obstetricians appreciate that routine antenatal care needs to be modified in order to provide optimal care to overweight, obese and morbidly obese women, this chapter aims to review the up‐to‐date evidence that will guide those adaptations. In adolescence, several studies have shown that obese teenagers may have a higher number of sexual partners, older partners and less use of contraception [4]. This is a worrying pattern that does not continue into adulthood, but does lead to concerns regarding pregnancy risk in a vulnerable group. For those not wishing to conceive, obesity may be a significant factor when considering contraceptive options. In contrast to adolescents, use of contraceptives does not differ in adult women based on BMI. The following points should be noted when discussing with obese women the most effective contraception. Safety of contraception should also be discussed at length, including the risk of thromboembolism with some forms of contraception. It is now well recognized that there is a reduction in fecundity in obese women. Median time to conception in obese women is 5 months, compared with 3 months for normal‐weight women. Various theories suggesting a causative mechanism have been proposed, including the following [5]. What is known is that the rate of pregnancy decreases by 5% for every unit of BMI over 29 kg/m2, even when controlled for PCOS, so there is an indirect correlation between higher BMI and fertility. Given the possible complications of obesity in pregnancy the ethics of providing subfertility treatment to obese women may be hotly debated, with some centres advocating that couples undergo weight loss prior to commencing any treatment. This is also an opportunity for pre‐pregnancy consultation, which will be outlined in more detail in the next section. Weight loss has been shown to increase conceptions, pregnancy and live births; in contrast, women desiring fertility treatment may be concerned regarding non‐modifiable factors such as age. Temporarily withholding fertility care may feel patriarchal, but may be an incentive to motivate women and their partners to achieve change. Even a weight loss of 10% of body weight can increase the rate of fertility, between 77 and 88%. The rate of spontaneous conception was doubled (to 35%), a figure comparable to the success rates of some in vitro fertilization (IVF) programmes; this suggests that weight reduction should be used as a primary tool prior to embarking on other forms of fertility treatment. When undergoing fertility treatment, women who are obese face additional challenges, including: Even in those where fertility treatment is successful, there are still increased risks to pregnancy, including increased risk of prematurity following IVF pregnancy in obese women. This risk of prematurity occurs at all ages of gestation, from viability to term. The risk of prematurity is also seen in twin deliveries following IVF; women with increased BMI are twice as likely to delivery twins prior to 28 weeks’ gestation when compared with women with a normal BMI and a twin pregnancy. Women with pre‐existing medical diseases (e.g. diabetes, cardiac disease, chronic autoimmune diseases) are advised that if they are considering a pregnancy to participate actively in multidisciplinary pre‐pregnancy counselling. This aims not just to inform the woman and her partner of the possible risks of pregnancy but also to modify behaviour and medical care in order to best prepare her for a pregnancy. Obesity, given the significant risks of maternal and fetal morbidity, should be regarded similarly. Indeed, this may be a more productive consultation, as the risk factor is modifiable in a way that cardiac disease and autoimmune disease may not be. Women who present for pre‐pregnancy consultations self‐select to inform themselves and make decisions. Empowering women to make changes can influence not just their health but also the risks of obesity to their pregnancies and their children. Most of the studies reviewing the effects of lifestyle intervention focus on pregnancy itself, but expert opinion suggests that pre‐pregnancy interventions hold considerable potential to improve maternal metabolic health. Opportunities for these consultations include general practice review visits, gynaecological reviews and fertility consultations as well as specialist obstetrics visits with multidisciplinary input. Unlike other long‐term diseases, obesity is modifiable, with even small differences in weight significantly reducing the risks to both mother and child. In addition, women who have undergone bariatric surgery (even if their BMI has normalized) should be counselled regarding the requirement for supplementation after surgery, especially in the context of pregnancy. Nutritional support needs to be tailored both to the patient and the type of surgery she had; an appropriately trained dietitian should ideally provide this. As an example, women who have undergone bariatric surgery may require supplemental calcium, iron, vitamin B12, vitamin A, folic acid, iodine and vitamin K [6]. It is advised that pregnancy should be avoided for 1 year after bariatric surgery because of the rapid weight loss and because malabsorption may increase the rate of intrauterine growth restriction, neural tube defects, neonatal hypoglycaemia and low birthweight. Weight loss following bariatric surgery is associated with a reduction in the rate of GDM, hypertension and pre‐eclampsia and with reduced pregnancy‐related weight gain. Concerns have been raised regarding mechanical complications during pregnancy as a result of pregnancy‐related vomiting, increased intra‐abdominal pressure and repositioning of the abdominal organs to facilitate fetal and uterine growth. Band migration, band leakage, dehydration, herniation and rotation as well as electrolyte disturbances have been described [5]. Some women may choose to undergo tubal ligation concurrently to bariatric surgery. Screening for obesity‐related comorbidities (such as type 2 diabetes, chronic hypertension, sleep apnoea, proteinuria, non‐alcoholic fatty liver disease and cardiac disease) would be valuable. Specific comorbidities such as ischaemic heart disease may be a relative contraindication to pregnancy. Women should be advised not to smoke cigarettes as this is an additional modifiable risk factor for morbidity and mortality. It has been suggested that those with a history of PCOS specifically should have a cardiovascular risk assessment due to the association with metabolic syndrome. Such an assessment could include family history, waist circumference, blood pressure, glycaemic control (e.g. oral glucose tolerance test) as well as a lipid profile [5]. Weight and height should be measured accurately in order to assess BMI and appropriately advise risks. Special bariatric equipment may be required, for example blood pressure should be measured with an appropriately sized cuff in order to most accurately measure a baseline and assess risk. Bariatric scales may be appropriate. Because of the relative malnutrition associated with obesity – where the maternal diet may comprise mostly of carbohydrates and fat, high in calories, with minimal minerals and vitamins – it is generally recommended that obese and overweight women should take a higher dose of folic acid than normal‐weight women. A dose of 4–5 mg, similar to that for women with diabetes, epilepsy or a family history of neural tube defects, should be encouraged. Women should be encouraged to enter pregnancy with a BMI below 30, ideally below 25. Weight is a very personal issue: being labelled ‘obese’ or ‘morbidly obese’ may upset women. They are much more than just their weight. At all times care and communication should be conducted sensitively and respectfully. For many women, especially those with a BMI just over the obese range, the booking visit may be the first opportunity for education regarding the impact of obesity on pregnancy, delivery and their children. Because of sensitivities regarding the personal nature of weight and self‐image, clinicians may shy away from the challenge of counselling women of the risks of obesity. Some may believe that little can be gained from it as the pregnancy has already started and significant weight loss will not be achievable. Advice regarding exercise, weight gain, nutritional choices and screening for complications such as GDM are appropriate, as pregnancy is a window of opportunity where women are motivated to adopt lifestyle changes. It is important that this advice is repeated, and from multiple angles from different clinicians. An honest discussion means that all members of the team caring for a pregnant woman with obesity approach the pregnancy openly and give the woman information on what may happen in her pregnancy. Similar to the pre‐pregnancy consultation, the first booking visit can be an opportunity to screen for pre‐existing disease in order to be able to accurately discuss prognosis. Weight and height should be measured to assess BMI. Self‐reporting of weight is unreliable. Blood pressure should be measured with an appropriately sized cuff to establish pregnancy baseline. Pregnant obese women have been shown to have a diet high in saturated fats and inadequate in carbohydrates, calcium, iron, folate and vitamin D [7]. These micronutrients are crucial for pregnancy. If not already started, consideration should be given to prescribing high‐dose folic acid in order to reduce the risk of neural tube defects (it is obviously best to commence this before conception). Depending on the location, consideration can also be given to supplementation with vitamin D (e.g. 400 IU) as obesity predicts poor vitamin D status in both mother and neonate. This will depend on maternal exposure to sunlight of appropriate wavelength and clothing (e.g. those living in cooler climates as well as those with more restrictive clothing). It is also recommended that obese pregnant women lower their intake of processed high‐fat foods and confectionary, with a concomitant increase in complex carbohydrates (wholegrain rice, pasta, bread and cereals) in order to be able to improve macronutrient intake by diet. A specific referral to a dietitian for individualized advice may be required, especially for women with a BMI over 40. Women who have lost weight since a previous pregnancy or a pre‐pregnancy consultation should be congratulated: even a small loss of weight can reduce the morbidity associated with a pregnancy affected by obesity. Advice regarding gestational weight gain can be gently but assertively given; the Institute of Medicine recommends a total weight gain in pregnancy of 5–8 kg in obese women [8] (Table 16.2). This is not just for the pregnancy but also for long‐term health, since the strongest predictor of weight retention at 1 year post partum is weight gain in pregnancy. Table 16.2 Institute of Medicine recommendations for total weight gain and rate of weight gain in pregnancy, based on pre‐pregnancy BMI (kg/m2) Source: Institute of Medicine and National Research Council. Weight Gain During Pregnancy: Reexamining the Guidelines. Washington, DC: National Academies Press, 2009. * Ranges in italic represent kilogram equivalents. Provided there are no obstetric or medical contraindications, obese women should be encouraged to exercise during and after pregnancy, just as with normal‐weight women. Self‐reporting shows that one‐third of obese pregnant women are compliant with exercise in pregnancy guidelines; this may be reviewed with caution as a consistent finding is that obese women will over‐report activity and under‐report dietary intake [7]. Written comments in the medical notes should be factual and non‐judgemental. There is no current evidence that one model of antenatal care is superior to any other for obese pregnant women. A dedicated obesity clinic may stigmatize women. Depending on the population demographics, the services may be overwhelmed if the ‘bar’ for admission is set too low. In contrast, however, a dedicated clinic may not only send a message that obesity is being taken seriously by all members of the multidisciplinary team, but also allow for a package of care to be provided that is consistent to all participants. Women who have undergone bariatric surgery prior to pregnancy have specific needs to maximize the health of the pregnancy. Those with gastric banding may need bands to be loosened during pregnancy. Dietetic input is essential in order to ensure adequate nutritional intake. This advice may also apply to women who have achieved a normal BMI after surgery, given the nature of the surgery to cause malabsorption. There are several case reports of internal bowel rotation during pregnancy following gastric bariatric surgery. Women presenting with severe upper abdominal pain should have urgent surgical assessment as they may require emergency laparotomy and bowel excision. Some of these case reports have also described emergency caesarean delivery at the time of laparotomy; others have described preterm delivery or intrauterine demise in the postoperative period in pregnancies at gestations of very early viability. Although the association between obesity and GDM is well described, it is interesting that a universal theme amongst women with a new diagnosis of GDM is their shock at the diagnosis. This experience was independent of BMI: even those with morbid obesity were surprised and upset at a diagnosis of GDM. Whether the local guidelines suggest risk factor‐based or universal screening, women should be screened between 24 and 28 weeks’ gestation. Consideration should be given to screening earlier in women with significant risk factors, such as morbid obesity, as discussed in the sections on booking visit and pre‐pregnancy consultations. Where the screening test and diagnostic tests are positive for GDM in obese and morbidly obese women, strong consideration should be given to repeating the test in the postnatal period due to the heterogeneity of GDM, with some women having underlying undiagnosed type 2 diabetes. It is equally important to gently inform women with GDM, especially those with obesity and morbid obesity, that pregnancy can be considered a ‘treadmill test’ for future health, and that a diagnosis of GDM is a prognostic indicator for increased risk of diabetes later in life. Modification of risk factors may affect the prognosis. Obesity is a risk factor for essential hypertension, pregnancy‐induced hypertension and pre‐eclampsia. This is why it is crucially important to accurately measure blood pressure at both booking visits (to establish baseline) and at subsequent visits in order to screen for both pregnancy‐induced hypertension and pre‐eclampsia. Nulliparous morbidly obese women (BMI >40) have a 30% chance of developing pre‐eclampsia. The risk of both early and late‐onset pre‐eclampsia is increased in obesity. Stages in the pathogenesis of pre‐eclampsia (cytotrophoblast migration, placental ischaemia, release of placental factors into the maternal circulation, maternal endothelial and vascular dysfunction) are increased as a result of obesity‐related metabolic factors [9].
Obesity and Pregnancy
BMI
Class
<19.9
Underweight
20–24.9
Normal weight
25–29.9
Overweight
30–34.9
Obese class I (‘mild’)
35–39.9
Obese class II (‘moderate’)
40+
Obese class III (‘morbid’)
Contraception, fertility and conception
Pre‐pregnancy consultation
When?
Bariatric surgery
Screening and general advice
Maternal complications: gestational diabetes, pre‐eclampsia and pregnancy‐induced hypertension
Pre‐pregnancy BMI
Total weight gain range (lbs)
Rate of weight gain in second and third trimester (mean range, pounds per week)
<19.9 (underweight)
28–40
(12.7–18.2) *
1 (1–1.3)
0.45 (0.45–0.6) *
20–24.9 (normal weight)
25–35
(11.4–15.9)
1 (0.8–1)
0.45 (0.36–0.45)
25–29.9 (overweight)
15–25
(6.8–11.4)
0.6 (0.5–0.7)
0.27 (0.23–0.32)
30+ (obese, all classes)
11–20
(5.0–9.1)
0.5 (0.4–0.6)
0.23 (0.18–0.27)
Dedicated clinics
Pregnancy following bariatric treatment
Gestational diabetes
Hypertension and hypertensive disorders
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