Public health need and practice

About half of women of childbearing age are either overweight (BMI 25 to 29.9 kg/m²) or obese (BMI greater than or equal to 30 kg/m²) (The NHS Information Centre 2008).

At the start of pregnancy, 15.6% of women in England are obese (Heslehurst et al. 2010).

Maternal obesity and weight retention after birth are related to socioeconomic deprivation (Heslehurst et al. 2010).

Health risks for obese women and their babies

Women who are obese when they become pregnant face an increased risk of complications during pregnancy and childbirth. These include the risk of impaired glucose tolerance and gestational diabetes, miscarriage, pre-eclampsia, thromboembolism and maternal death (Centre for Maternal and Child Enquiries and the Royal College of Obstetricians and Gynaecologists 2010).

Even a relatively small gain of 1 to 2 BMI units (kg/m2) between pregnancies may increase the risk of gestational hypertension and gestational diabetes, even in women who are not overweight or obese. It also increases the likelihood of giving birth to a large baby (Villamor and Cnattingius 2006).

An obese woman is more likely to have an induced or longer labour, instrumental delivery, caesarean section or postpartum haemorrhage (Yu et al. 2006). Reduced mobility during labour can result in the need for more pain relief, which can be difficult to administer in obese women, resulting in increased need for general anaesthesia with its associated risks. After birth, wound healing can be slower with an increased risk of infection, and obese women are more likely to require extra support in establishing breastfeeding, due to, for example, difficulties in latching the baby on to the breast (Heslehurst et al. 2007).

Obese women may also experience reduced choices about where and how they give birth. There may be restrictions on home births, the use of birthing pools and types of pain relief that can be given.

Obese women who are pregnant are likely to spend longer in hospital than those with a healthy weight because of morbidity during pregnancy and labour related to their weight (Chu et al. 2008). In the longer term, weight control after pregnancy may reduce the woman's risk of obesity, coronary heart disease, some cancers and type 2 diabetes.

Babies born to obese women also face several health risks. These include a higher risk of fetal death, stillbirth, congenital abnormality, shoulder dystocia, macrosomia and subsequent obesity (Ramachenderan et al. 2008).

Weight gain during pregnancy

US Institute of Medicine guidelines (Rasmussen and Yaktine 2009), based on observational data, state that healthy American women who are a normal weight for their height (BMI 18.5 to 24.9) should gain 11.5 to 16 kg (25 to 35 pounds) during pregnancy. Overweight women (BMI 25 to 29.9) should gain 7 to 11.5 kg (15 to 25 pounds) and obese women (BMI greater than 30) should only put on 5 to 9 kg (11 to 20 pounds).

Observational studies of American women suggest that those who gain weight within the Institute of Medicine ranges are more likely to have better maternal and infant outcomes than those who gain more or less weight. (The evidence is stronger for some outcomes – such as postpartum weight retention and birthweight – than for others [Siega-Riz et al. 2009]).

There are no formal, evidence-based guidelines from the UK government or professional bodies on what constitutes appropriate weight gain during pregnancy.

The Committee on Medical Aspects of Food Policy report on dietary reference values recommends that women should only have around 200 calories more a day in the last trimester of pregnancy (DH 1991). UK health professionals do not, as a matter of course, give women information about the risks of obesity and the importance of weight management before or during pregnancy (Heslehurst et al. 2007a). Pregnant women are advised not to diet, and to talk to their GP or midwife if they are concerned about their weight (Department of Health 2009).

Weight management after pregnancy

NICE's guideline on obesity identified the period after pregnancy and childbirth as a time when women are likely to gain weight. In addition, many conceive again during this period. Hence, managing the woman's weight in the first few years after childbirth may reduce her risk of entering the next pregnancy overweight or obese.

However, after having a child, many mothers find it difficult to eat a healthy diet and take regular exercise (Hewison and Dowswell 1994). It may be because women receive little or no advice on weight management after childbirth.

Women who exclusively breastfeed their infants for the first 6 months may require around an additional 330 calories a day. Some of these additional calories will be derived from fat stores. An additional 400 calories a day may be required for the second 6 months if they continue to breastfeed (DH 1991).

Breastfeeding is often recommended as a strategy for promoting weight loss, but findings from studies are mixed (Gore et al. 2003). The additional energy requirements of breastfeeding may help some women return to their pre-pregnancy weight. If women are moderately active on a regular basis, this will not adversely affect a woman's ability to breastfeed and could aid weight management.

The Department of Health (2009) does not make specific recommendations on weight management after childbirth. It advises against following a restricted-calorie diet while breastfeeding and suggests that women should talk to their GP if they feel they need to lose weight. However, there is no national guidance for professionals.

Women on low incomes may be eligible for Healthy Start vouchers to buy fruit and vegetables (as well as milk and infant formula). These are available to pregnant women and families with a child aged under 4 years. Those eligible include people on income support and income-based jobseekers allowance and those with low incomes. All pregnant women under 18 years also qualify, whether or not they are on state benefits.