Description of the condition
Overweight and obesity (body mass index (BMI) ≥ 25.0 to 29.9 kg/m
Overweight and obesity are known to be associated with many adverse general health conditions such as hypertension (Kurukulasuriya 2011), diabetes (Reaven 2011) and PCOS (polycystic ovary syndrome) (Gambineri 2002). PCOS is a common cause of decreased fertility (also known as infertility/subfertility, or failure to achieve pregnancy within a specific timeframe) in women of reproductive ages (Hull 1987) and is associated with several late pregnancy complications (Bjercke 2002). Whilst overweight and obesity is associated with reduced fertility, the specific preconception management of women with known subfertility will not be discussed in this review as it is discussed in another Cochrane review (Anderson 2010).
During pregnancy overweight or obese women are at increased risk of experiencing a miscarriage (Frederick 2013), developing impaired glucose tolerance (decreased ability to control blood glucose levels) (Frederick 2013), sleep apnea (a sleep disorder involving pauses in breathing) (Frederick 2013), pre-eclampsia (pregnancy-related hypertension), chorioamnionitis (infection of the amniotic fluid surrounding the infant or of the membranes) (Raatikainen 2006) and preterm birth (Catalano 2006; Galtier 2008). There are additional risks of complications during labour and birth, including the need for induction of labour or caesarean birth (Catalano 2006), and also the risk of postpartum haemorrhage. Throughout the pregnancy and after the birth, overweight or obese women are also at higher risk of venous thromboembolism (a blood clot in the veins that can then break off and spread to other parts of the body) (Gray 2012).
Infants born to women who are overweight or obese are at increased risk of congenital abnormalities such as neural tube defects (a defect in the formation of the brain and/or spinal cord), structural heart defects and gastrointestinal malformations (Waller 2007). The infant is also more likely to have high birthweight (macrosomia) (Catalano 2006), which can result in increased risk of birth trauma and maternal complications (Oral 2001). Macrosomia is also recognised as a risk factor for subsequent child and adulthood obesity and its consequences (Birbilis 2012).
Description of the intervention
Preconception care is a collection of health interventions designed to best prepare and improve the woman’s physical and emotional health to increase the likelihood of a successful pregnancy and healthy infant (Whitworth 2009). It has many components and can be implemented in many ways depending on the resources available and the individual needs of the woman.
Preconception care for the general population may include advice about alcohol intake and smoking, as well as exercise, nutritional supplementation and immunisations. Less attention however, has been paid to the needs of specific subgroups of women, including women who are overweight and obese, who may benefit from specific and targeted interventions. This may include diet and lifestyle advice, active management of co-morbid medical conditions or bariatric surgery.
How the intervention might work
Women who are overweight and obese may benefit from a structured approach to preconception counselling, aiming to reduce the risks of the specific overweight and obesity complications outlined above. This approach may involve a preconception assessment of the woman's health, which could be followed by a directed and individualised plan to optimise the woman's health. This approach may include the following.
Education is an important part of preconception counselling. Informing women about the risks associated with overweight and obesity during pregnancy may allow them to make informed decisions about their pregnancy plans and timing of conception.
Preconception screening for health conditions associated with obesity
Obesity prior to pregnancy is associated with many conditions including hypertension (high blood pressure) (Kurukulasuriya 2011), impaired glucose tolerance and diabetes (Reaven 2011) and sleep apnea (Mehra 2008). Many of these conditions can be exacerbated by pregnancy. By screening for these conditions prior to conception there is the opportunity to optimise the woman's health by treating these co-morbid conditions prior to conception. For example, for some women, it might be advised to await stabilisation of blood pressure or some degree of weight loss prior to conceiving.
Management of sleep apnea
Sleep apnea during pregnancy has been associated with an increased risk of developing hypertensive disease of pregnancy and gestational diabetes (Priscilla 2013). Intensive lifestyle interventions have been shown, in the general population, to reduce apnea-associated complications and improve rates of remission (Kuna 2013). The effect of preconception interventions for sleep apnea and the outcomes for subsequent pregnancies has not been established.
Folic acid supplementation is well established as an important component of preconception care in the general population, reducing the incidence of neural tube defects. Women who are overweight and obese are reported to have lower serum folate levels (Tinker 2012), although there is no evidence to suggest that higher folate supplementation doses are beneficial. Women who are overweight or obese are reported to be less likely to take supplements during pregnancy, when compared with the general population (Case 2007).
Regular physical activity is recommended for all individuals as part of a healthy lifestyle. There are many benefits of regular physical activity including improved cardiovascular health (Metkus 2010) and improved bone density (Howe 2011). Moderate physical exercise has been shown to be safe (Larsson 2005) and has many benefits before and during pregnancy. Women who engage in regular physical activity in the preconception period are more likely to continue this during pregnancy.
General improvement of nutrition and health
Assessment of the overall nutrition of the overweight or obese women is important as it provides the building blocks for the infant. While under-nutrition is well recognised as being problematic for the pregnancy and future of the infant, over-nutrition also has implications. Infants born to women who are overweight or obese are at greater risk of having a high birthweight, which predisposes to future obesity and metabolic syndrome (Desai 2013). Not only is weight itself important but also the quality of the diet.
Many other factors affect body weight including genetics, psychological state, caloric intake and energy output. Previous Cochrane reviews have demonstrated that weight reduction is achievable in individuals who are overweight or obese with the use of low glycaemic index diets and psychological interventions, especially when these interventions are combined with exercise (Shaw 2009; Thomas 2009). Weight reduction as part of a pre-pregnancy plan may assist in lowering BMI and potentially decreasing pregnancy risk. For particular groups there may be an indication for surgical intervention to assist in weight management, and this includes gastric bypass surgery and gastric balloon insertion.
Bariatric surgery, regardless of whether restrictive (reducing the volume of food that can be consumed) or malabsorptive (reducing the area in the gastrointestinal system available to absorb nutrients), has been shown to have positive effects on many of the complications of obesity, including, diabetes, sleep apnea, dyslipidaemia and hypertension in the general population (Noria 2013). Some studies have shown improved pregnancy outcomes in obese women who have undergone bariatric surgery particularly with regards to reducing the burden of hypertensive disease of pregnancy (Bennett 2010) and diabetes (Weintraub 2008). Unfortunately, some studies have also shown increased risk of nutritional deficiencies following bariatric surgery (Bebber 2011). Surgical interventions for weight control may be indicated in some groups of women who may be at higher risk of hypertensive complications who are resistant to other interventions.
Other Cochrane reviews in this area
There are Cochrane reviews already in place that address issues in this general area. We have listed them here and described differences between the existing reviews and our planned review.
Some address care specifically before during or after pregnancy.
The review by Amorim Adegboye et al (Diet or exercise, or both, for weight reduction in women after childbirth (Amorim Adegboye 2013)) includes only breastfeeding women in the postpartum period and only includes outcomes for the mother and current child, not related to pregnancy.
The review by Furber et al (Antenatal interventions for reducing weight in obese women for improving pregnancy outcome (Furber 2013)) looks at weight control in the antenatal period. Our currently planned review is assessing preconception interventions.
A number of reviews in particular address different aspects of preconception care.
A review by Tieu et al in 2010 entitled Preconception care for diabetic women for improving maternal and infant health (Tieu 2010) includes women with pre-existing diabetes, and this group has been specifically excluded from this review.
The review by Whitworth and colleagues (Routine pre-pregnancy health promotion for improving pregnancy outcomes (Whitworth 2009)) excludes trials where interventions are aimed specifically at women with established medical, obstetric or genetic risks or already receiving treatment as part of programmes for high-risk groups and examines routine health promotion for all women.
In contrast, the review by Anderson and colleagues (Preconception lifestyle advice for people with subfertility (Anderson 2010)) is specific to those women seeking fertility treatment and this group has been excluded from this review.
The Tieu review (Interconception care for women with a history of gestational diabetes for improving maternal and infant outcomes (Tieu 2013)) only included women with a history of gestational diabetes. Our review will be looking at women with a larger range of preconception conditions, and specifically those with a BMI in the overweight or obese range.
Why it is important to do this review
Overweight and obesity are increasingly common among women of reproductive age and are associated with adverse outcomes for women and their infants. There is currently no evidence to indicate whether directed preconception health programs are of benefit, and if so, what they should include. It is important to determine which interventions, if any, are of benefit to women who are overweight or obese and how they should be implemented to improve pregnancy outcomes.
To systematically review the effects of a directed intervention or program of preconception care for women who are overweight or obese, compared with no specific preconception care or routine preconception care on pregnancy outcomes.
Criteria for considering studies for this review
Types of studies
Randomised controlled trials will be included, excluding those only published as an abstract. Quasi-randomised trials and trials using a cross-over design will not be included. Cluster-randomsied trials will be included. The intervention in these studies would involve an assessment of preconception health and lead to an individualised preconception program addressing any areas of concern for that particular woman.
Types of participants
Women who are not pregnant, but of reproductive age (as defined by trial authors) who have a body mass index (BMI) greater than or equal to 25 kg/m
Types of interventions
Preconception interventions that involve any or all of: provision of specific information, screening for and treating obesity-related health problems, customised or general dietary and exercise advice, medical or surgical interventions. Medical interventions may include treatment of pre-existing hypertension, impaired glucose tolerance or sleep apnea. Surgical interventions may include interventions such as bariatric surgery.
The comparator will be standard preconception advice or no advice/interventions.
Types of outcome measures
The primary infant outcome will be large-for-gestational-age infants (greater than 90
- Perinatal death (stillbirth and neonatal death)
- Infant birthweight greater than 4500 g
- Infant birthweight less than 2500 g
- Admission to neonatal intensive care unit
- Admission to the neonatal nursery
- Length of hospital stay for the neonate
- Birth trauma (nerve palsy or fracture)
- Shoulder dystocia
- BMI at three years of age
- Childhood neurodevelopment (as defined by trial authors)
- Childhood atopy/allergy
- Satisfaction with care (as defined by trial authors)
- Quality of life (as defined by trial authors)
- Physical health (as defined by trial authors)
- Emotional health (as defined by trial authors)
- Time to conception
- Use of assisted reproductive technology
- Need for antenatal hospital stay
- Antepartum haemorrhage requiring hospitalisation
- Gestational diabetes (as defined by trial authors)
- Hypertensive disease of pregnancy
- Preterm birth before 37 weeks' gestation
- Gestational weight gain
- Need for induction of labour
- Caesarean section
- Perineal trauma
- Postpartum haemorrhage (as defined by trial authors)
- Postnatal length of stay
- Thromboembolic disease
- Breastfeeding at six months postpartum
Search methods for identification of studies
We will contact the Trials Search Co-ordinator to search the Cochrane Pregnancy and Childbirth Group’s Trials Register.
The Cochrane Pregnancy and Childbirth Group’s Trials Register is maintained by the Trials Search Co-ordinator and contains trials identified from:
- monthly searches of the Cochrane Central Register of Controlled Trials (CENTRAL);
- weekly searches of MEDLINE;
- weekly searches of Embase;
- handsearches of 30 journals and the proceedings of major conferences;
- weekly current awareness alerts for a further 44 journals plus monthly BioMed Central email alerts.
Details of the search strategies for CENTRAL, MEDLINE and Embase, the list of handsearched journals and conference proceedings, and the list of journals reviewed via the current awareness service can be found in the ‘Specialized Register’ section within the editorial information about the Cochrane Pregnancy and Childbirth Group.
Trials identified through the searching activities described above are each assigned to a review topic (or topics). The Trials Search Co-ordinator searches the register for each review using the topic list rather than keywords.
Searching other resources
In addition, we will search reference lists of retrieved studies.
We will not apply any language restrictions.
Data collection and analysis
Selection of studies
Two review authors will independently assess for inclusion all the potential studies we identify as a result of the search strategy. We will resolve any disagreement through discussion or, if required, we will consult a third person.
Data extraction and management
We will design a form to extract data. For eligible studies, two review authors will extract the data using the agreed form. We will resolve discrepancies through discussion or, if required, we will consult a third person. We will enter data into Review Manager software (RevMan 2012) and check for accuracy.
When information regarding any of the above is unclear, we will attempt to contact authors of the original reports to provide further details.
Assessment of risk of bias in included studies
Two review authors will independently assess risk of bias for each study using the criteria outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). We will resolve any disagreement by discussion or by involving a third assessor.
(1) Random sequence generation (checking for possible selection bias)
We will describe for each included study the method used to generate the allocation sequence in sufficient detail to allow an assessment of whether it should produce comparable groups.
We will assess the method as:
- low risk of bias (any truly random process, e.g. random number table; computer random number generator);
- high risk of bias (any non-random process, e.g. odd or even date of birth; hospital or clinic record number);
- unclear risk of bias.
(2) Allocation concealment (checking for possible selection bias)
We will describe for each included study the method used to conceal allocation to interventions prior to assignment and will assess whether intervention allocation could have been foreseen in advance of, or during recruitment, or changed after assignment.
We will assess the methods as:
- low risk of bias (e.g. telephone or central randomisation; consecutively numbered sealed opaque envelopes);
- high risk of bias (open random allocation; unsealed or non-opaque envelopes, alternation; date of birth);
- unclear risk of bias.
(3.1) Blinding of participants and personnel (checking for possible performance bias)
We will describe for each included study the methods used, if any, to blind study participants and personnel from knowledge of which intervention a participant received. We will consider that studies are at low risk of bias if they were blinded, or if we judge that the lack of blinding would be unlikely to affect results. We will assess blinding separately for different outcomes or classes of outcomes.
We will assess the methods as:
- low, high or unclear risk of bias for participants;
- low, high or unclear risk of bias for personnel.
(3.2) Blinding of outcome assessment (checking for possible detection bias)
We will describe for each included study the methods used, if any, to blind outcome assessors from knowledge of which intervention a participant received. We will assess blinding separately for different outcomes or classes of outcomes.
We will assess methods used to blind outcome assessment as:
- low, high or unclear risk of bias.
(4) Incomplete outcome data (checking for possible attrition bias due to the amount, nature and handling of incomplete outcome data)
We will describe for each included study, and for each outcome or class of outcomes, the completeness of data including attrition and exclusions from the analysis. We will state whether attrition and exclusions were reported and the numbers included in the analysis at each stage (compared with the total randomised participants), reasons for attrition or exclusion where reported, and whether missing data were balanced across groups or were related to outcomes. Where sufficient information is reported, or can be supplied by the trial authors, we will re-include missing data in the analyses which we undertake.
We will assess methods as:
- low risk of bias (e.g. no missing outcome data; missing outcome data balanced across groups, or maximum of 20% missing data);
- high risk of bias (e.g. numbers or reasons for missing data imbalanced across groups; ‘as treated’ analysis done with substantial departure of intervention received from that assigned at randomisation);
- unclear risk of bias.
(5) Selective reporting (checking for reporting bias)
We will describe for each included study how we investigated the possibility of selective outcome reporting bias and what we found.
We will assess the methods as:
- low risk of bias (where it is clear that all of the study’s pre-specified outcomes and all expected outcomes of interest to the review have been reported);
- high risk of bias (where not all the study’s pre-specified outcomes have been reported; one or more reported primary outcomes were not pre-specified; outcomes of interest are reported incompletely and so cannot be used; study fails to include results of a key outcome that would have been expected to have been reported);
- unclear risk of bias.
(6) Other bias (checking for bias due to problems not covered by (1) to (5) above)
We will describe for each included study any important concerns we have about other possible sources of bias.
We will assess whether each study was free of other problems that could put it at risk of bias:
- low risk of other bias;
- high risk of other bias;
- unclear whether there is risk of other bias.
(7) Overall risk of bias
We will make explicit judgements about whether studies are at high risk of bias, according to the criteria given in the Cochrane Handbook (Higgins 2011). With reference to (1) to (6) above, we will assess the likely magnitude and direction of the bias and whether we consider it is likely to impact on the findings. We will explore the impact of the level of bias through undertaking sensitivity analyses - see Sensitivity analysis.
Measures of treatment effect
For dichotomous data, we will present results as summary risk ratio with 95% confidence intervals.
For continuous data, we will use the mean difference if outcomes are measured in the same way between trials. We will use the standardised mean difference to combine trials that measure the same outcome, but use different methods.
Unit of analysis issues
We will include cluster-randomised trials in the analyses along with individually-randomised trials. We will adjust their sample sizes using the methods described in the Cochrane Handbook [Section 16.3.4] using an estimate of the intracluster correlation co-efficient (ICC) derived from the trial (if possible), from a similar trial or from a study of a similar population. If we use ICCs from other sources, we will report this and conduct sensitivity analyses to investigate the effect of variation in the ICC. If we identify both cluster-randomised trials and individually-randomised trials, we plan to synthesise the relevant information. We will consider it reasonable to combine the results from both if there is little heterogeneity between the study designs and the interaction between the effect of intervention and the choice of randomisation unit is considered to be unlikely.
We will also acknowledge heterogeneity in the randomisation unit and perform a sensitivity analysis to investigate the effects of the randomisation unit.
Multiple armed trials
We will include multi-armed trials and attempt to overcome potential unit of analysis errors by combining groups to create a single pairwise comparison or select one pair of interventions and exclude the others.
Dealing with missing data
For included studies, we will note levels of attrition. We will explore the impact of including studies with high levels of missing data in the overall assessment of treatment effect by using sensitivity analysis.
For all outcomes, we will carry out analyses, as far as possible, on an intention-to-treat basis, i.e. we will attempt to include all participants randomised to each group in the analyses, and all participants will be analysed in the group to which they were allocated, regardless of whether or not they received the allocated intervention. The denominator for each outcome in each trial will be the number randomised minus any participants whose outcomes are known to be missing.
Assessment of heterogeneity
We will assess statistical heterogeneity in each meta-analysis using the T², I² and Chi² statistics. We will regard heterogeneity as substantial if an I² is greater than 30% and either a T² is greater than zero, or there is a low P value (less than 0.10) in the Chi² test for heterogeneity.
Assessment of reporting biases
If there are 10 or more studies in the meta-analysis, we will investigate reporting biases (such as publication bias) using funnel plots. We will assess funnel plot asymmetry visually. If asymmetry is suggested by a visual assessment, we will perform exploratory analyses to investigate it.
We will carry out statistical analysis using the Review Manager software (RevMan 2012). We will use fixed-effect meta-analysis for combining data where it is reasonable to assume that studies are estimating the same underlying treatment effect: i.e. where trials are examining the same intervention, and the trials’ populations and methods are judged sufficiently similar. If there is clinical heterogeneity sufficient to expect that the underlying treatment effects differ between trials, or if substantial statistical heterogeneity is detected, we will use random-effects meta-analysis to produce an overall summary, if an average treatment effect across trials is considered clinically meaningful. The random-effects summary will be treated as the average range of possible treatment effects and we will discuss the clinical implications of treatment effects differing between trials. If the average treatment effect is not clinically meaningful, we will not combine trials.
If we use random-effects analyses, the results will be presented as the average treatment effect with 95% confidence intervals, and the estimates of T² and I².
Subgroup analysis and investigation of heterogeneity
If we identify substantial heterogeneity, we will investigate it using subgroup analyses and sensitivity analyses. We will consider whether an overall summary is meaningful, and if it is, use random-effects analysis to produce it.
We plan to carry out the following subgroup analyses.
- Women who are overweight versus those who are obese.
Subgroup analysis will be restricted to the review's primary outcome.
We will assess subgroup differences by interaction tests available within RevMan (RevMan 2012). We will report the results of subgroup analyses quoting the χ2 statistic and P value, and the interaction test I² value.
We plan to carry out sensitivity analyses to explore the effects of trial quality as assessed by concealment of allocation or missing data for a particular outcome on the summary statistic. We plan to exclude studies of poor quality from the analysis in order to assess for any substantive difference to the overall result. Sensitivity analysis will be restricted to the primary outcome.
As part of the pre-publication editorial process, this protocol has been commented on by three peers (an editor and two referees who are external to the editorial team), members of the Pregnancy and Childbirth Group's international panel of consumers and the Group's Statistical Adviser.
The National Institute for Health Research (NIHR) is the largest single funder of the Cochrane Pregnancy and Childbirth Group. The views and opinions expressed therein are those of the authors and do not necessarily reflect those of the NIHR, NHS or the Department of Health.
Contributions of authors
Nicolle Opray is the contact person and guarantor for the review and designed the review and wrote the protocol, with review of content by Rosalie Grivell, Andrea Deussen and Jode Dodd.
Declarations of interest
Nicolle Opray and Andrea Deussen: None known.
Jodie Dodd and Rosalie Grivell are planning to carry out an RCT that may be eligible for inclusion in this review in the future. All decisions relating to any such study (i.e. assessment for inclusion and trial quality, data extraction) will be carried out by other members of the review team who are not directly involved in the study.