Preconception and maternal obesity: epidemiology and consequences

In Europe, whilst most countries do not systematically report obesity rates in their pregnant population, the prevalence of maternal obesity varies from 7 to 25 %^{(Reference Devlieger, Benhalima and Damm12)}. More specifically, in Great Britain, between 2015 and 2017, it was estimated that 21·8 % of women giving birth were living with obesity, although 16·9 % did not have a BMI recorded in their medical notes, suggesting the prevalence could be greater^{(Reference Relph, Coe and Carroll13)}. Obesity in women has been linked to a number of adverse reproductive outcomes including delayed time to conception, increased rate of miscarriage and later pregnancy complications, such as gestational diabetes, instrumental and caesarean birth, preterm birth and large for gestational age (LGA) babies^{(Reference Marchi, Berg and Dencker14,Reference Santos, Voerman and Amiano15)} . The effects of obesity may be worsened by the high incidence of abnormal glucose tolerance and excessive gestational weight gain (GWG) found in this group^{(Reference Devlieger, Benhalima and Damm12)}.

Recommendations on appropriate GWG are based on pre pregnancy BMI, with those who start pregnancy in the overweight or obese categories advised to gain less weight than those in the healthy weight or underweight categories^{(Reference Rasmussen and Yaktine16)}. Both excess and inadequate GWG are linked to adverse outcomes such as preterm birth, infant death and offspring weight status in childhood^{(Reference Marchi, Berg and Dencker14,Reference Goldstein, Abell and Ranasinha17–Reference Rogozinska, Zamora and Marlin19)} . Due to the abundant evidence that overweight and obesity prior to pregnancy and excessive GWG incur perinatal risks, it is increasingly emphasised that aiming for achievement of a healthy weight before conception is fundamental^{(Reference Stephenson, Heslehurst and Hall20–Reference Poston, Caleyachetty and Cnattingius22)}. A wealth of research exists investigating the most effective intervention for weight loss in this population group, however, no one strategy is effective^{(Reference Price and Sumithran23–Reference Musgrave, Cheney and Dorney26)}, meaning more extreme interventions, such as weight loss medications^{(Reference Salamun, Jensterle and Janez27)} or surgery may be sought.

Overview of weight loss surgery

Weight loss surgery, also known as ‘bariatric’ or ‘metabolic’ surgery, is a viable treatment option for people with severe and complex obesity (BMI ≥ 40 kg/m²)⁽²⁸⁾. It can result in significant and sustained weight loss^{(Reference Sjostrom, Lindroos and Peltonen29)}, with a Cochrane review demonstrating that surgery results in greater improvement in weight loss and weight-associated comorbidities, compared with non-surgical interventions, regardless of the type of surgical procedure used^{(Reference Colquitt, Pickett and Loveman30)}. Nevertheless, weight regain is not uncommon, and revisional surgery may be required where complications arise^{(Reference Athanasiadis, Martin and Kapsampelis31,Reference Noria, Shelby and Atkins32)} . Bariatric surgery modifies the anatomy and functioning of the gastrointestinal tract, leading to changes in capacity and nutrient absorption. Although bariatric surgery was historically categorised as either restrictive, reducing the size of the stomach, and/or malabsorptive, reducing absorption of nutrients, this is over simplistic and it is now understood that more complex neuroendocrine mechanisms contribute to weight loss and metabolic improvements^{(Reference Pucci and Batterham33–Reference Miras and le Roux35)}. Common procedures include sleeve gastrectomy (SG), Roux-en-Y gastric bypass (RYGB) and laparoscopic adjustable gastric banding (LAGB), although other surgery types and subtypes exist.

Following bariatric surgery, eating habits need to adapt to the new gastrointestinal physiology, which ultimately results in a lower energy intake^{(Reference Busetto, Dicker and Azran11,Reference Janmohammadi, Sajadi and Alizadeh36)} . Procedure-specific nutritional problems and symptoms may occur, which may be complicated by pre-existing nutritional deficiencies^{(Reference Benotti, Wood and Dove37)} and/or disordered eating behaviours^{(Reference Opozda, Chur-Hansen and Wittert38)}. Because of this greatly reduced energy and nutrient intake, protein intake should be optimised^{(Reference Busetto, Dicker and Azran11,Reference Mechanick, Youdim and Jones39)} and daily lifelong supplementation with multiple micronutrients, including iron, calcium and vitamin D is advised^{(Reference O’Kane, Parretti and Pinkney10)}. Regular laboratory surveillance for nutritional deficiencies is recommended, and supplementation should be individualised accordingly by a registered dietitian^{(Reference O’Kane, Parretti and Pinkney10,Reference Busetto, Dicker and Azran11)} .

Access to weight loss surgery

Eligibility for weight loss surgery in England is governed by National Institute for Health and Care Excellence criteria guidelines, which were updated in 2023⁽²⁸⁾. People should be offered a referral for assessment for surgery with a specialist weight management service if they meet the following criteria:

• Have a BMI ≥ 40 kg/m² or BMI between 35 and 39·9 kg/m² with a significant health condition that could be improved with weight loss and

• Agree to the necessary long-term follow up after surgery (for example, lifelong annual reviews)

Consideration should be given to those of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background using a lower BMI threshold (reduced by 2·5 kg/m²), to account for the fact that these groups are prone to central adiposity and their cardiometabolic risk occurs at a lower BMI⁽²⁸⁾.

At the initial assessment with the specialist weight management service, several factors will be considered, including:

• Whether all appropriate non-surgical measures have been tried

• Whether the person has or will receive intensive management in a tier 3 weight management service (a multidisciplinary specialist weight management clinic)

• General fitness for anaesthesia and surgery

• Nutritional status

The person’s ‘plans for conception and pregnancy (if someone is of childbearing age)’ is also noted as a factor which should be discussed at this stage.

However, given that 64 % of the adult population in England are living with overweight or obesity, demand for weight loss surgery outstrips supply^{(Reference Moody40)}. Indeed, a recent analysis of routinely collected primary care data in England from 2007 to 2020 reported that only 1 % of the 436 501 adults with severe and complex obesity underwent bariatric surgery^{(Reference Coulman, Margelyte and Jones41)}. A higher BMI and geographical location were the factors that were most strongly associated with undergoing bariatric surgery. The National Bariatric Surgery Registry⁽⁴²⁾ provides pooled national data to examine trends and outcomes in bariatric surgery. The most recent report with information up to August 2019 reported an average of approximately 6000–7000 procedures per year, with approximately 75 % conducted in the public National Health Service. Following the COVID-19 pandemic, the number of surgeries decreased to ∼1300/year in 2020 with a small increase to ∼2500/year in 2021/2022⁽⁴²⁾, underlying an increasing backlog of unmet need and the need to increase capacity^{(Reference Ghanem, Emile and Cousins43)}. This has led to an increase in bariatric tourism, whereby people travel abroad for weight loss surgery, motivated by exceedingly long waiting lists and lack of affordable private healthcare^{(Reference Azlan, Finucane and Flaherty44)}. Concerns have been raised about preoperative assessment and perioperative care^{(Reference Azlan, Finucane and Flaherty44)}, which includes nutritional follow-up and aftercare.

Weight loss surgery and fertility

Women with obesity who are intending to become pregnant take longer on average to conceive, and time to pregnancy increases with the degree of obesity^{(Reference Moxthe, Sauls and Ruiz45)}. Obesity can lead to ovulatory dysfunction, due to the associated suboptimal glycaemic control and insulin resistance. Overweight and obesity can also have a negative effect on fertility through their association with polycystic ovarian syndrome^{(Reference Lim, Davies and Norman46)}. Women with obesity referred for assisted reproductive technology may find restrictions are imposed until weight loss has occurred, due to potential complications of the surgical procedures and the lower positive fertility rate^{(Reference Gautam, Purandare and Maxwell47)}. In women with severe obesity, bariatric surgery may normalise hormonal abnormalities and improve fertility^{(Reference Edison, Whyte and van Vlymen48,Reference Lacey, Attersley-Smith and Stone49)} . Moxthe et al. ^{(Reference Moxthe, Sauls and Ruiz45)} undertook a systematic review to assess the impact of surgery on male and female fertility. A total of 18 articles, covering 16 349 individuals, were included in the final review, seven of which included only men, ten included only women and one included both men and women. Bariatric surgery significantly improved hormonal balance in both men and women, sperm count in men and pregnancy in women. However, evidence was weak with a lack of discussion on confounding variables, and many studies did not differentiate between surgery types^{(Reference Moxthe, Sauls and Ruiz45)}.

Research suggests that future pregnancy is important to 30·3 % of women under 45 years awaiting bariatric surgery^{(Reference Gosman, King and Schrope50)}, indicating that improved fertility may be a motivating factor to women seeking bariatric surgery. In 2019, women accounted for over 80 % of all gastric band insertions and 70 % of other weight loss surgery procedures⁽⁴²⁾, which does not reflect the gender specific obesity rates in the country^{(Reference Moody40)}. The relatively high rate of women undergoing weight loss surgery is not unique to the UK, with data from 51 countries from 2014 to 2018 indicates that 73·7 % of people who had surgery were female^{(Reference Welbourn, Hollyman and Kinsman4)}. A qualitative study of women in Sweden without children undertaken a few weeks prior to surgery supported the observation that improved fertility may be a motivating factor^{(Reference Nilsson-Condori, Järvholm and Thurin-Kjellberg51)}. Participants (n 12) were aware that obesity can lead to a high-risk pregnancy, with potential risks to both mother and offspring. Although the participants were not necessarily seeking bariatric surgery for fertility reasons alone, there was a perception of enhanced fertility after surgery, which was viewed as important. Interestingly, there was no perception or belief that surgery could affect future pregnancies in a negative manner. However, it is important to note that as a result of improved fertility after bariatric surgery, the risk of an unintended pregnancy may increase and unplanned pregnancy within six months of surgery is relatively common^{(Reference Vasilevski, Angel and Mathison52)}. Family planning is often not discussed in sufficient detail before surgery, and there is a need for improved advice around appropriate contraceptive and pregnancy planning in this high-risk group^{(Reference Shawe, Ceulemans and Akhter9,Reference Gosman, King and Schrope50,Reference Vasilevski, Angel and Mathison52)}

Timing of pregnancy after weight loss surgery

For all weight loss surgery patients, there is considerable risk of malnutrition if nutritional aftercare guidelines are not adhered to^{(Reference O’Kane, Parretti and Pinkney10,Reference Busetto, Dicker and Azran11)} . This risk is more pronounced for those in the preconception or early pregnancy phase. In addition to the routine nutritional supplementation guidance for all post-surgical patients, there are additional considerations around vitamin A, folic acid and more frequent biochemical monitoring for those planning pregnancy or already pregnant^{(Reference Shawe, Ceulemans and Akhter9,Reference O’Kane, Parretti and Pinkney10)} . It is generally recommended that pregnancy should be delayed for 12–18 months after surgery to reduce the potential for foetal malnutrition^{(Reference O’Kane, Parretti and Pinkney10,Reference Mechanick, Apovian and Brethauer53)} . International consensus guidance, based on a systematic review, recommends that pregnancy should be postponed until a stable weight is achieved^{(Reference Shawe, Ceulemans and Akhter9)}. which is typically achieved one year after SG or RYGB procedures and two years after LAGB. The systematic review identified 14 studies reporting on the surgery-to-conception interval and pregnancy outcomes; however, heterogenous methodology and outcome reporting made comparing results difficult^{(Reference Shawe, Ceulemans and Akhter9)}. The UK Royal College of Obstetricians and Gynaecologists recommends a more personalised approach, taking into account maternal age and balancing nutritional risk against the risk of delaying pregnancy in older women⁽⁵⁴⁾. Ultimately irrespective of which guidelines are followed, contraceptive counselling should be offered to this population group, with availability of specific preconception clinical services for those who are intending to become pregnant^{(Reference Stephenson, Heslehurst and Hall20)}.

Micronutrient deficiencies

In women who become pregnant after bariatric surgery, evidence suggests a better overall obstetric outcome in comparison to women with severe obesity managed conservatively; however, there is heightened risk of maternal nutritional deficiencies and infants born small for gestational age (SGA)^{(Reference Madden, Ferber and Cantwell8,Reference Kwong, Tomlinson and Feig55–Reference Akhter, Rankin and Ceulemans61)} . Micronutrient deficiency is very prevalent in the post-bariatric surgery population^{(Reference Lupoli, Lembo and Saldalamacchia62)}. This is particularly pronounced in pregnancy, due to the higher nutritional need for certain micronutrients, such as iron, folate and vitamin D⁽⁶³⁾. In the general post-bariatric surgery population, deficiency may be due to a combination of general or procedure-specific factors; including the type of surgery and risk of malabsorption, pre-surgical deficiences^{(Reference Benotti, Wood and Dove37)}, surgical complications, poor adherence to supplementation, food aversion/intolerance^{(Reference Nicoletti, de Oliveira and Barbin64)}, taste disturbances^{(Reference Shoar, Naderan and Shoar65)} or psychological factors. It is not known whether these factors affect pregnant women disproportionately and whether there is any interaction with pregnancy-related cravings^{(Reference Hill, Cairnduff and McCance66)} or nausea.

Routine biochemical monitoring of several micronutrients, including zinc and folate, is recommended in each trimester^{(Reference O’Kane, Parretti and Pinkney10)}. Depleted maternal concentrations of vitamins A, B₁₂, K, folate and iron post-bariatric surgery were reported in a 2015 systematic review^{(Reference Jans, Matthys and Bogaerts67)}; however, the quality of reporting was not rated highly. A more recent systematic review identified 27 studies, comprising 2056 women with pregnancies after bariatric surgery. Deficiencies were reported in maternal concentrations of vitamins A, B₁, B₆, B₁₂, C, D, K, iron, calcium, selenium and phosphorous^{(Reference Rottenstreich, Elazary and Goldenshluger68)}, indicating vast improvements are required in nutritionally monitoring and care of this group. Of the studies investigating nutrient intake in post-surgical pregnancies most focus on adherence to micronutrient supplementation, with a paucity of data available on food intake during pregnancy and most studies omitting critical information about methods of measuring dietary intake^{(Reference Maslin, James and Brown6,Reference Guthrie, Dix and Truby7)} . The limited available research suggests dietary patterns can be improved substantially^{(Reference Guelinckx, Devlieger and Donceel69,Reference Coupaye, Legardeur and Sami70)} ; however, qualitative research indicates that most women were given unhelpful or contradictory advice about diet and nutrition whilst pregnant^{(Reference Vasilevski, Angel and Mathison52)}. It is therefore recommended that pregnant women with a history of bariatric surgery are given intensive dietetic support, preferably by dietitians with experience of managing the nutritional complications of bariatric surgery, and closely monitored for nutritional deficiencies^{(Reference O’Kane, Parretti and Pinkney10)}. Improved understanding and characterisation of this population group would help to target services towards the women in most need of dietary support.

Specific nutrition recommendations for the preconception and pregnancy phases

Preconception phase

Given that over 50 % of pregnancies in the general population are unplanned, the preconception phase can be difficult to define^{(Reference Stephenson, Heslehurst and Hall20)}. Therefore, the need to make nutritional adjustments during the preconception phase should ideally be mentioned to all women of reproductive age who are considering surgery. In those planning pregnancy, the focus should remain on the regular monitoring of diet quality and nutritional status and on encouraging a general healthy dietary pattern and lifestyle. However, dietary needs may differ in terms of the food group proportions from that of the nonsurgical population before (and during pregnancy^{(Reference Shawe, Ceulemans and Akhter9)}). This is due to a greater emphasis on lean protein sources, followed by fruit and vegetables, and lastly starchy carbohydrates, as the main component of the post bariatric surgery diet.

It is recommended that pregnancy should be planned, and that diet quality and nutritional supplementation should be optimised preferably 3–6 months prior to conception^{(Reference Shawe, Ceulemans and Akhter9)}. The guidelines of the British Obesity and Metabolic Surgery Society are shown in Table 1 ^{(Reference O’Kane, Parretti and Pinkney10)}. They recommend that following all bariatric procedures, a complete multivitamin and mineral supplement (containing thiamine, iron, zinc, copper and selenium) is taken. Care should be taken to check that the micronutrient supplement contains sufficient amounts of vitamins and minerals to counter the malabsorptive effects of bariatric surgery; however, additional supplements will be needed and should be adjusted according to biochemical monitoring. This applies to those in the preconception and during pregnancy also^{(Reference O’Kane, Parretti and Pinkney10)}.

Table 1. Daily dose recommendations for micronutrient supplementation for adults post bariatric surgery, incorporating considerations for (pre) pregnancy supplementation^{(Reference O’Kane, Parretti and Pinkney10)}

RYGB: Roux en Y gastric band, SG: Sleeve gastrectomy.

Vitamin and mineral supplements should be reviewed regularly and adjusted accordingly^{(Reference O’Kane, Parretti and Pinkney10)}.

All women planning for pregnancy should take folic acid supplements to reduce the risk of foetal neural tube defects. Prior to conception and until the 12th week of pregnancy, 400 μg/d folic acid is recommended. Women with a BMI > 29·9 kg/m² or who have diabetes should take a higher dose of folic acid of 4 or 5 mg/d during the periconception period and throughout the first trimester^{(Reference Denison, Aedla and Keag71,72)} . Vitamin B₁₂ should be measured during the preconception period before additional folic acid supplements are given. Vitamin B₁₂ regimens should be continued at a dose of 1 mg every 3 months via intramuscular depot injection or alternatively, oral supplementation (1 mg/d) can be used to increase compliance in the patient^{(Reference Shawe, Ceulemans and Akhter9)}. Vitamin A in the retinol form is teratogenic^{(Reference Rothman, Moore and Singer73)}, so it should be replaced with vitamin A in the beta carotene form. This may be achieved by taking a preconception or pregnancy-specific vitamin and mineral supplement^{(Reference O’Kane, Parretti and Pinkney10)}; however, the levels of other micronutrients in these preparations should be checked to ensure they are adequate. Regular laboratory surveillance for nutritional deficiencies is recommended and supplementation should be individualised accordingly^{(Reference Shawe, Ceulemans and Akhter9,Reference O’Kane, Parretti and Pinkney10)} . A more frequent review with the specialist bariatric dietitian may be required during this phase^{(Reference O’Kane, Parretti and Pinkney10)} to provide individualised advice.

Biochemical monitoring during pregnancy

Routine biochemical monitoring of several micronutrients, including zinc and folate is recommended to occur in each trimester^{(Reference Shawe, Ceulemans and Akhter9–Reference Busetto, Dicker and Azran11)} as listed in Table 2. Vitamin E, zinc, copper and selenium should be monitored during the first trimester. During pregnancy, serum levels of many micronutrients and macronutrients will decrease because of the expanding maternal blood volume and increasing demands of the growing foetus. Accordingly, reference values for serum micronutrient levels may change during pregnancy, and it is useful to check results against pregnancy-specific reference ranges^{(Reference O’Kane, Parretti and Pinkney10)}.

Table 2. Recommended biochemical monitoring during each trimester of pregnancy^{(Reference O’Kane, Parretti and Pinkney10)}

Post bariatric patients with prolonged vomiting are at risk of thiamine deficiency; this may occur in pregnant women with severe pregnancy sickness. Clinicians should be aware of the signs of thiamine deficiency and prescribe 300 mg daily with vitamin B complex. Furthermore, intravenous thiamine should be given at a minimum dose of 100 mg daily with intravenous vitamin B complex if oral supplementation with a B vitamin-complex is not possible due to the severity of vomiting^{(Reference Shawe, Ceulemans and Akhter9)}.

Current developments in obesity management and future research needs

With women making up the majority of people having bariatric surgery⁽⁴²⁾, there is need for many evidence gaps surrounding pregnancy to be filled. Consensus European expert guidelines on periconception, antenatal and postnatal care written in 2019^{(Reference Shawe, Ceulemans and Akhter9)} highlighted many gaps in relation to bariatric surgery; namely how best to meet nutritional needs with food, optimal screening and supplementation strategy for micronutrient deficiencies before and during pregnancy, how to ensure safe and acceptable gestational weight gain, in addition to how best to communicate advice around pregnancy planning. However, since then, the onset of the COVID-19 pandemic has further limited the number of surgeries being conducted, with demand and eligibility far outstripping supply^{(Reference Coulman, Margelyte and Jones41)}. Simultaneously, new pharmaceutical weight loss therapies, Glucagon Like Peptide-1 Receptor Agonists (GLP-1RA), have been licenced for use in the UK^(79,80) , which have been evaluated for use both prior^{(Reference Rubio-Herrera, Mera-Carreiro and Sánchez-Pernaute81)} to and after bariatric surgery^{(Reference Mok, Adeleke and Brown82)}. Although GLP-1RAs are contraindicated during pregnancy^(83,84) and there are concerns about inhibition of absorption of oral contraceptives⁽⁸⁵⁾, there is evidence for their use in improving fertility in those with PCOS^{(Reference Salamun, Jensterle and Janez27)}. Ultimately more research about the effect of GLP-1RAs on reproductive health outcomes in women is needed^{(Reference Schultes, Ernst and Timper86)}, especially as they may be accessed without a prescription and potentially may be sought by those who are seeking improvements in fertility whilst facing a prolonged wait for surgery. With the recent publication of the women’s health strategy for England⁽⁸⁷⁾ and pledge to improve funding and research into women’s reproductive health from its current low level^{(Reference Guthrie, Catherine and Leach88)}, it is hoped that both the research and the implementation of novel research findings around maternal weight loss and pregnancy outcomes will accelerate in the coming years.