The Public Health Interventions Advisory Committee (PHIAC) took account of a number of factors and issues when developing the recommendations.
3.1 PHIAC was keen to adopt a 'life course approach' to this guidance, noting that pregnancy and around a year after childbirth are key points in a woman's life when she may gain excess weight. PHIAC also recognised that weight management can be difficult in the current obesogenic environment. Sedentary habits and a high calorie diet are common and physical activity, such as walking, is not part of daily life. However, the period before, during and after pregnancy does provide an opportunity to give women practical advice to help them to improve their diet, become more physically active or to help them manage their weight effectively. To ensure this opportunity is not missed, the recommendations emphasise the need for practical advice that takes into account the woman's particular social and economic circumstances and involves the whole family.
3.2 PHIAC recognised that health professionals would welcome UK guidance on weight gain in pregnancy. In the absence of such guidance, PHIAC discussed whether it would be appropriate to support the US Institute of Medicine's guidelines. These guidelines, which were revised in 2009, are based on observational data. The data show that women who gained weight within the specified ranges had better outcomes than those who did not. However, the recommendations were not validated by intervention studies. Without evidence from large-scale trials, it is not clear whether or not adhering to the recommended ranges lowers the risk of adverse outcomes for mothers and their babies. In addition, the guidelines were developed for the US population and it is not known whether or not they would apply to other populations with a different ethnic composition. PHIAC was therefore unable to support their use without more evidence and more information about their applicability to the UK population. This is an important area for future research.
3.3 PHIAC recognised that not only does weight gain in pregnancy vary between individuals, but that the components involved also vary. Weight gain in pregnancy is made up of the fetus, placenta, amniotic fluid, and increases in maternal blood and fluid volume, as well as an increase in body fat.
3.4 PHIAC noted the lack of intervention studies on weight management during pregnancy. Those that do exist are pilot studies with small sample sizes and insufficient statistical power to detect differences in health outcomes for mothers and their babies. Several large-scale, randomised controlled trials are underway worldwide, but no conclusions could be drawn from them before publication of this guidance. PHIAC agreed to draw on existing NICE guidance which is based on evidence of effectiveness and cost effectiveness. This includes public health guidance on maternal and child nutrition and behaviour change and clinical guidelines on obesity, antenatal care and postnatal care.
3.5 PHIAC emphasised the importance of women being a healthy weight before pregnancy. Pre-pregnancy BMI is a greater determinant of healthy outcomes for mothers and babies than any weight they may gain during pregnancy. Women with a high BMI might also find it more difficult to conceive.
3.6 For many women, the first year or two after birth is a time when they start to think about having another baby. Weight management during this time will help them to achieve a healthy weight when they next become pregnant – and help prevent incremental weight gain over successive pregnancies.
3.7 The guidance is targeted at women who are actively planning a pregnancy and those who are already pregnant or who have had a baby. It is, however, recognised that a population-based approach is important in reaching all women of childbearing age, as many pregnancies are unplanned.
3.8 Women receive a wealth of sometimes conflicting advice on what constitutes a healthy diet and how much physical activity they should do during pregnancy and after childbirth. This comes not just from health professionals and official sources but from family, friends, the media and new media (such as social networking sites). For example, the press regularly publishes celebrity claims of unrealistic and rapid weight loss after pregnancy. This may create additional pressure on women to lose weight inappropriately at an already stressful time.
3.9 Concern about obesity or weight gain in pregnancy might lead some women to try to lose weight. Dieting is not advised during pregnancy because it is not known whether it is safe. Restrictive or 'crash' diets may increase blood ketone levels and could adversely affect the neuro-cognitive development of the fetus.
3.10 PHIAC was aware that the health risks of being overweight or obese during pregnancy, for both the mother and her unborn child, are not routinely discussed. Health professionals recognise the risks but are often unsure what advice to give. In some cases, they lack the training, skills or confidence to discuss weight management. In addition, they may not know how to tailor advice and support for women who are pregnant.
3.11 The needs of pregnant teenagers may differ from those of pregnant older women. Their social circumstances may differ, as may the health professionals they come into contact with. For example, they may be cared for by specialist teenage pregnancy midwives and teenage pregnancy support nurses. In addition to supporting the growth of the baby, pregnant teenagers may still be growing themselves.
3.12 Some population groups, such as Asians, face co-morbidity risk at a lower BMI than other groups. However, there is no consensus on how to define overweight and obesity in different ethnic groups for women of childbearing age.
3.13 The period following childbirth is a time of great change for women and their partners, as they learn to cope with the demands of a new baby. Lack of sleep and a range of physical and psychological problems, such as backache, urinary and faecal incontinence, depression and fatigue, are common. These problems can be compounded when they are caring for another child (or children) as well. Some health problems may impact on a woman's ability to be physically active and therefore, her ability to manage her weight.
3.14 The additional energy requirements of breastfeeding may help some women return to their pre-pregnancy weight. Those who are breastfeeding and do not increase their energy intake, eat a healthy diet and are moderately active will be more likely to achieve this. Although it cannot be assumed that all women who breastfeed will lose weight, PHIAC considered it important to encourage exclusive breastfeeding for the first 6 months because of the wider health benefits for both the mother and her baby.
3.15 PHIAC noted that after childbirth, women may resume smoking and drinking alcohol. These habits may also affect their weight.
3.16 After the birth of their baby, women may not be in regular contact with health services and may need local, community-based sources of support to help them manage their weight.
3.17 PHIAC discussed the role of children's centres in working with pregnant women and their families in particular, working with teenage parents and families from low income and black and minority ethnic groups. Children's centre services might include: antenatal education, appropriate maternity services (including early antenatal engagement and postnatal support), breastfeeding promotion and support and advice on how to combat obesity and enjoy a healthy diet.
3.18 On balance, interventions during pregnancy were considered to be cost effective. However, the estimate of cost effectiveness was subject to considerable uncertainty. Weight management interventions during the 6 months after birth also appeared to be cost effective, but the results were sensitive to assumptions made in the modelling. PHIAC was mindful that most of the recommendations did not increase costs in the long term and, as they could be expected to do more good than harm, they are likely to be cost effective. Furthermore, some of the advice has been adapted from previous NICE guidance which has already been shown to be cost effective.