Obesity is increasing; in the UK, almost 20% of pregnant women have a body mass index (BMI) of ≥30 kg/m 2 . Obese mothers have increased risks of pregnancy complications including miscarriage, congenital anomaly, gestational diabetes, pre-eclampsia, macrosomia, induction of labour, caesarean section, anaesthetic and surgical complications, post-partum haemorrhage, infection and venous thromboembolism. Complications tend to be greater in those with the highest BMIs. In recent triennia, obesity (27–29%) was over-represented in maternal mortality figures. Strategies to reduce morbidity and mortality include calculating BMI at booking visit to identify obese mothers and plan their antenatal care and delivery. This should include nutritional and lifestyle advice, screening for gestational diabetes and pre-eclampsia, thromboembolism risk assessment, antenatal anaesthetic review if BMI is ≥ 40 kg/m 2 , ensuring availability of robust theatre tables and other equipment and involving senior doctors, especially in the labour ward. Afterwards, continuing weight reduction should be encouraged to reduce future pregnancy and health risks.
Highlights
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Maternal morbidity can be reduced by identifying women with BMI≥30 kg/m 2 and following guidelines.
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Folic acid, vitamin D, and if other risks for pre-eclampsia, aspirin 75 mg are advised.
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Availability of suitable beds and other equipment should be checked before admission.
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Senior obstetricians and anaesthetists are advised for women with BMI ≥ 40 kg/m 2 in labour.
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Active placental delivery, thromboprophylaxis and vigilance for infection reduce risk.
Worldwide, obesity has almost doubled since 1980 . In the United States, more than one-third of women are obese, more than one-half of pregnant women are overweight or obese and 8% of women of reproductive age are extremely obese . In England, obesity among women has increased from 16.4% in 1993 to 25.1% in 2012, with similar trends in Scotland and Wales . Obesity in pregnancy has also increased from 9–10% in the early 1990s to 16–19% in the 2000s . A 3-year study of maternal obesity in the UK found that 4.99% of pregnant women who gave birth at ≥24 weeks had a body mass index (BMI) of ≥35 kg/m 2 , 2.01% had a BMI of ≥40 kg/m 2 (Class III obesity/morbidly obese) and 0.19% had a BMI of ≥50 kg/m 2 (super-morbid or extreme obesity) . The UK Obstetric Surveillance System (UKOSS) national cohort study of extreme obesity estimated a prevalence of 8.7 cases per 10,000 deliveries (95% confidence interval (CI) 8.1–9.4) or almost one in 1000 .
Obesity is over-represented in maternal mortality figures
In 2000–2002, 29% of all direct and indirect pregnancy-related deaths in the UK occurred in obese women with a BMI of ≥30, compared with a 23% incidence of obesity in the general population . This trend continued in the subsequent two triennia where 27% of the women who died from direct or indirect causes had a BMI of ≥30 kg/m 2 . The 2003–2005 Confidential Enquiry into Maternal Deaths (CEMD) report observed that obesity was especially predominant among the women who died from thromboembolism, sepsis and cardiac disease; for some extremely obese women, appropriate equipment was not readily available or their weight caused difficulties in moving, resuscitation or surgical access . This report made several recommendations including pre-pregnancy counselling and weight loss, public health messages, better statistical information about the prevalence of obesity and development of a national guideline . The Centre for Maternal and Child Enquiries (CMACE)/Royal College of Obstetricians and Gynaecologists (RCOG) Joint National Guideline for the Management of Women with Obesity in Pregnancy published in March 2010 will hopefully reduce obesity-related maternal mortality and morbidity .
Obesity contributes to maternal and foetal morbidity
Obesity is associated with an increased incidence of complications and adverse outcomes at all stages of pregnancy and in the puerperium. These include miscarriage, venous thromboembolism (VTE), pre-eclampsia, gestational diabetes mellitus (GDM), dysfunctional labour, induction of labour, operative vaginal delivery, caesarean section, general anaesthesia, post-partum haemorrhage and wound infections . For the foetus, congenital anomalies, placental problems, prematurity, large-for-gestational-age babies, stillbirth, neonatal death and lower rates of breastfeeding are more common, and the children of obese women are more likely to become obese themselves . In the UKOSS study of women whose BMI was ≥50 kg/m 2 , extreme obesity was associated with increased risks of pre-eclampsia, gestational diabetes, preterm delivery, caesarean section, general anaesthesia and intensive care unit admission; complications tended to be greater in those with the highest BMIs although there were no maternal deaths among the 665 women studied .
Obesity contributes to maternal and foetal morbidity
Obesity is associated with an increased incidence of complications and adverse outcomes at all stages of pregnancy and in the puerperium. These include miscarriage, venous thromboembolism (VTE), pre-eclampsia, gestational diabetes mellitus (GDM), dysfunctional labour, induction of labour, operative vaginal delivery, caesarean section, general anaesthesia, post-partum haemorrhage and wound infections . For the foetus, congenital anomalies, placental problems, prematurity, large-for-gestational-age babies, stillbirth, neonatal death and lower rates of breastfeeding are more common, and the children of obese women are more likely to become obese themselves . In the UKOSS study of women whose BMI was ≥50 kg/m 2 , extreme obesity was associated with increased risks of pre-eclampsia, gestational diabetes, preterm delivery, caesarean section, general anaesthesia and intensive care unit admission; complications tended to be greater in those with the highest BMIs although there were no maternal deaths among the 665 women studied .
How can these risks be minimised?
Identifying women at risk
The first, crucial step is to identify obese women as early as possible so that a management plan for antenatal care, delivery and afterwards can be made. Obesity in pregnancy is usually defined as a BMI of ≥30 kg/m 2 at the first antenatal (booking) visit . All pregnant women at their booking visit, which should ideally take place by 10 weeks of gestation, should have their height and weight measured accurately using appropriate equipment (not a ‘guesstimate’ or figures provided by the woman in lieu of actual measurement), their BMI calculated and a record made in their clinical notes and electronic patient record . A BMI of ≥30 kg/m 2 should trigger an individualised care plan designed to optimise well-being and minimise risk. A simple checklist commenced and placed in the woman’s notes at booking can be a useful aide-memoire for the busy midwife or clinician ( Fig. 1 ).
Who should care for obese women in their pregnancies?
The type of antenatal care should be decided at the booking visit, taking into account the degree of obesity and any pre-existing risk factors. Women with a booking BMI of ≥35 kg/m 2 are recommended to be under surveillance during pregnancy in accordance with the Pre-eclampsia Community Guideline . This guideline advises that women with a booking BMI of ≥35 kg/m 2 who have no other risk factors for pre-eclampsia can be monitored in the community, but if they have one or more additional risk factors for pre-eclampsia they should be referred early in pregnancy to a specialist . However, Saving Mothers Lives 2006–2008 advises that women with a BMI of ≥35 kg/m 2 are unsuitable for midwifery-only care and should be seen in pregnancy by a consultant obstetrician as obesity is an important risk factor for thromboembolism ; the National Institute for Health and Care Excellence (NICE) Clinical Guideline on Intrapartum Care advises that women with a BMI of ≥35 kg/m 2 should give birth in a consultant-led unit with appropriate neonatal services as they are at a higher risk of complications, such as shoulder dystocia and post-partum haemorrhage, which require immediate obstetric intervention .
Most maternity hospitals do not have the resources to provide a specialist antenatal clinic, so all obstetricians, midwives and general practitioners (GPs) need to be familiar with the specific issues surrounding obesity in pregnancy, and clear policies and guidelines should be available in all antenatal clinics .
Managing nutrition and weight gain in pregnancy
Dieting during pregnancy is not recommended as it may harm the health of the unborn child , but it is important to offer advice and support to avoid excessive weight gain. Women with a BMI of ≥30 kg/m 2 should be offered at the booking appointment a referral to a dietitian or an appropriately trained health professional for assessment and personalised advice on healthy eating and how to be physically active . Small but increasing numbers of women are becoming pregnant after bariatric surgery; this does reduce their risk of obesity-related complications but they may need nutritional supplementation with iron, calcium, folate and vitamins D and B12, and may need their gastric band surgically adjusted during pregnancy .
Congenital anomalies are more common
A systematic review found that obese women, compared with mothers of normal BMI, had a significantly increased risk of pregnancy affected by neural tube, cardiovascular, orofacial, anorectal and limb reduction anomalies, whereas the risk of gastroschisis was significantly reduced . The suggested mechanisms included: undiagnosed diabetes and hyperglycaemia, as obesity has similar metabolic abnormalities to diabetes; nutritional deficiencies; and underdetection of structural anomalies due to difficulties in ultrasound visualisation, resulting in fewer terminations and increased birth prevalence. As gastroschisis is more common in young women, its decreased risk was attributed to the correlation between obesity and increasing maternal age . In a study of maternal obesity and ultrasound detection of foetal anomalies, there was a significant failure to detect structural anomalies, especially cardiac anomalies, in obese women, which increased significantly with increasing maternal BMI ( p = 0.001), and in women with pregestational diabetes ( p < 0.001) . No association has been described between maternal obesity and the prevalence of Down syndrome until a recently published 16-year Swedish study of 1,568,604 women, many of whom did not have prenatal screening, found maternal obesity in early pregnancy to be associated with an increased risk of Down syndrome in the newborn; however, prenatal screening with combined ultrasound and biochemistry appeared to be equally effective irrespective of BMI.
Strategies to maximise the detection of foetal structural anomalies in obese women include using high-definition ultrasound equipment, a comfortably full maternal bladder to improve visualisation, if necessary repeating the scan a few weeks later and, in women with higher BMIs, considering a transvaginal anatomy scan in the early second trimester.
Preventing congenital anomalies
Weight reduction before or between pregnancies will help to reduce the incidence of congenital anomalies and other risks associated with obesity. Bariatric surgery before pregnancy does not seem to affect the risk of congenital malformations . There is little information about the teratogenic effects of anti-obesity drugs. The UK teratology information service advises that orlistat (Xenical), the only anti-obesity drug currently listed in the British National Formulary, should be discontinued as soon as pregnancy is diagnosed, as it may impair the absorption of fat-soluble vitamins and there are theoretical concerns that rapid weight loss during pregnancy may restrict nutrient availability to the foetus . Optimising the control of existing diabetes prior to conception reduces the risk of congenital malformations .
Periconceptual folic acid supplementation reduces the risk of the first occurrence as well as the recurrence of neural tube defects . As women with a BMI >27 kg/m 2 have lower folate levels, even after controlling for folate intake, compared with women with BMI <27 kg/m 2 , it is recommended that women with a BMI of ≥30 kg/m 2 hoping to become pregnant be advised to take a higher dose (5 mg) of folic acid supplementation daily, starting at least 1 month before conception and continuing during the first trimester of pregnancy .
Vitamin D supplementation is recommended
Vitamin D is a fat-soluble vitamin that is important for bone health to prevent osteomalacia and rickets. Although small amounts are present in foods such as oily fish and eggs, the main source of vitamin D is its synthesis in skin exposed to sunlight. In the UK and other northern countries, there is not always enough sunlight of adequate intensity to maintain good levels of vitamin D, especially in those who spend a lot of time indoors or have darker skin. Obesity is associated with vitamin D deficiency; pre-pregnancy BMI is inversely associated with serum levels of vitamin D in obese pregnant women and their neonates . A Cochrane systematic review concluded that vitamin D supplementation during pregnancy increases maternal serum vitamin D levels at term but further randomised controlled trials are needed to evaluate the role of vitamin D supplementation in pregnancy . The current recommendation is that pregnant and breastfeeding women with a booking BMI of ≥30 kg/m 2 should take 10 mcg of vitamin D supplement daily .
Gestational diabetes is increased
Women who develop GDM have an increased risk of giving birth to large-for-gestational-age babies, which increases the likelihood of obstetric interventions such as induction of labour and caesarean section; for the baby, there is an increased likelihood of birth trauma, the possibility of transient neonatal morbidity that may require admission to the neonatal unit and an increased risk of becoming obese or developing diabetes in later life .
A BMI of ≥30 kg/m 2 is an independent risk factor for gestational diabetes ; maternal obesity has a threefold increased risk of GDM compared with women of a healthy weight . Treatment, compared with routine care, in a randomised controlled trial of 1000 women with GDM was shown to reduce the risk of serious adverse perinatal outcome (death, shoulder dystocia, bone fracture and/or nerve palsy) (adjusted OR 0.33; 95% CI 0.14–0.75; p = 0.01) . The risk of most of these adverse outcomes increases with increasing levels of hyperglycaemia with no clear cut-off point or threshold .
Screening for gestational diabetes in obese pregnant women and careful management of those who develop this condition will contribute to the reduction of both maternal and foetal morbidity. Both the NICE Clinical Guideline No.63 and the CMACE/RCOG Joint Guideline recommend that all pregnant women with a booking BMI of ≥30 kg/m 2 be screened for gestational diabetes at 24–28 weeks using the 2-h 75-g oral glucose tolerance test (GTT) and the criteria for diagnosis defined by the World Health Organization . Measuring maternal haemoglobin A1C does not appear to be a useful alternative to an oral GTT .
Preventing VTE
Deep venous thrombosis, pulmonary embolism and cerebral venous thrombosis cause acute symptoms; they may also result in long-term morbidity and sometimes maternal death. Obesity is considered a moderate risk factor for VTE; it is important because of its high prevalence and because the risk appears to increase with increasing obesity . Weight was the most important risk factor for maternal death from pulmonary embolism in the 2006–2008 triennium; nine of the 16 women who died had a BMI of ≥30 kg/m 2 , including one with a BMI of >40 kg/m 2 . Obesity was one of the main risk factors for antenatal pulmonary embolism (aOR 2.65, 95% CI 1.09–6.45) in the UKOSS case–control study between February 2005 and August 2006 .
VTE has been the leading cause of direct maternal mortality in the UK in almost all triennia since the Confidential Enquiries into Maternal Deaths began in 1952. Many of these deaths were preventable. Concern about the high number of maternal deaths after caesarean section in the early 1990s led to recommendations for post-operative thromboprophylaxis that reduced the number of deaths from VTE . Subsequent guidelines recommended thromboprophylaxis for those with moderate or high risk factors after vaginal delivery and antenatally . The effect of these guidelines has already been seen in the most recently published triennium (2006–2008) where maternal deaths from thrombosis and thromboembolism had fallen significantly to 18 (maternal mortality rate (MMR) 0.79 per 100,000 maternities, 95% CI 0.49–1.25) compared with 41 (MMR 1.94 per 100,000 maternities, 95% CI 1.43–2.63) in the previous triennium . The number of deaths from cerebral venous thrombosis also fell in 2006–2008; cerebral venous thrombosis has similar risk factors to pulmonary embolism and both women who died from this cause were morbidly obese .
Despite all the recommendations for risk assessment and thromboprophylaxis in the series of guidelines produced since 1995, thromboembolism has remained a leading cause of direct maternal mortality. Although it has long been recognised that obesity is an important risk factor for VTE, it is only in the most recent version of the RCOG guideline that recommendations have been made to increase the dose of thromboprophylaxis depending on body weight ( Table 1 ), so further reductions in maternal mortality from VTE may be seen in future. Much more can still be done – inadequate risk assessment, inadequate thromboprophylaxis, failure to investigate chest symptoms and failure to ensure multidisciplinary care when it would have been appropriate contributed to some maternal deaths from VTE in 2006–2008 .
