disease in patients with Type 2 diabetes. N Engl J Med 2003; 343: 383, 393.
The Dietary Management of Diabetic Pregnancies ANNE DORNHORST AND GARY FROST Imperial School of Medicine, London, UK
INTRODUCTION
There are general nutritional principles that apply to all pregnancies and there are specific nutritional issues that surround the management of pregnant women with diabetes.
The nutritional needs of women with pre-existing Type 1 diabetes and Type 2 diabetes differ, as do those for women who become glucose-intolerant in pregnancy.
Ideally nutritional advice should start before pregnancy and continue throughout the pregnancy, being modified as necessary at each antenatal visit.
The dietitian is an integral part of the multidisciplinary diabetic, obstetric team and should be involved in all aspects of the patient’s care plan.
The prescribed diet has to accommodate the metabolic and physiological changes associated with a diabetic pregnancy and the dietitian must be familiar with these changes.
Over the last few decades the Western antenatal population has become older, more obese, less physically active and more ethnically diverse.
These demographic changes explain the rise in the numbers of pregnant women with pre-existing Type 2 diabetes and gestational diabetes (1).
Although the actual number of pregnant women with pre-existing Type 1 diabetes has remained relatively constant, the duration of diabetes prior to pregnancy has increased, due to women delaying childbirth for personal reasons and the earlier onset of Type 1 diabetes that has occurred over recent years.
Both the age of the mother and the duration of her diabetes contribute to the clinical
Nutritional Management of Diabetes Mellitus. Edited by G. Frost, A. Dornhorst and R. Moses & 2003 John Wiley & Sons, Ltd. ISBN 0 471 49751 7
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complications encountered in a Type 1 diabetic pregnancy. Although pregnancy outcomes continue to improve in women with Type 1 diabetes, perinatal morbidity and mortality remain fourfold higher than for the non- diabetic population (2,3). Active dietary management for all types of diabetic pregnancies can lessen complications during pregnancy and improve pregnancy outcome for the mother and her child.
CONSEQUENCES OF A DIABETIC PREGNANCY
Maternal hyperglycaemia results in an excess maternal, foetal transfer of glucose.
The placental glucose transporter protein, GLUT1, is increased in diabetic pregnancies, and maternal hyperglycaemia quickly results in foetal hyperglycaemia and foetal hyperinsulinaemia (4).
Maternal hyperglycaemia is not only a critical factor in glucose-mediated congenital malformations, but also in many aspects of foetal development, neonatal well-being and future health, see Table 7.1.
An accelerated foetal growth pattern and a large-for-gestational-age (LGA) infant at birth is the hallmark of a poorly controlled diabetic pregnancy.
Foetal insulin is the main foetal anabolic hormone and hyperinsulinaemia can cause excess fat accumulation, organomegaly, especially of the heart and liver, and high birthweight.
An LGA infant is a potential cause for birth trauma and a high Caesarean rate.
Foetal hyperinsulinaemia is also believed to contribute to adverse foetal metabolic complications in late pregnancy including a tendency to high lactate levels and an increased risk of stillbirth.
Foetal hyperinsulinae- mia at delivery can cause transient hypoglycaemia and hypocalcaemia.
There is increasing and tantalising evidence that by optimising maternal glycaemia and avoiding foetal hyperinsulinaemia one can reduce the long-term risk of the child becoming obese and insulin-resistant in adult life (5).
Table 7.1 The intrauterine influence of maternal hyperglycaemia on foetal and childhood development
Period of influence Consequence of maternal hyperglycaemia
First trimester Congenital malformations Second trimester Foetal cell programming, foetal hyperinsulinaemia Third trimester Accelerated foetal growth and stillbirth Neonatal period Transient hypoglycaemia; hypocalcaemia and cardiomyopathy Adolescence Obesity, impaired glucose tolerance and insulin resistance Adulthood Insulin resistance, obesity and Type 2 diabetes
THE DIETARY MANAGEMENT OF DIABETIC PREGNANCIES 93
THE THERAPEUTIC AIM IN THE MANAGEMENT OF DIABETIC PREGNANCIES
The aim in the management of all diabetic pregnancies is to achieve normoglycaemia while avoiding maternal hypoglycaemia.
This approach will optimise foetal growth and minimise short- and long-term complications.
As the immediate post-prandial period is when maternal glucose levels are at their highest, dietary and insulin therapies need to specifically target this time (6).
The glycaemic targets for all types of diabetic pregnancies should be the same, namely a fasting glucose of <5 mmol/l and a 1 h post-prandial glucose <7.8 mmol/l.
While these goals will inevitably require insulin in women with pre-pregnancy diabetes, many women with gestational diabetes (GDM) will be able to achieve them with dietary intervention alone, with insulin being reserved for women who, after a trial of dietary therapy, are above these glycaemic target values.
The use of oral agents that do not cross the placenta, such as glibenclamide, in the management of GDM, although probably safe, are best suited for women with Type 2 diabetes and GDM in areas of the world where insulin availability is limited (7).
Due to the lack of adequate controlled dietary studies in diabetic pregnancies, conflicting dietary advice is often advocated.
Debate still surrounds the total energy content of the diet and the optimal proportions and type of dietary carbohydrate and fat to be prescribed.
The benefits, if any, of whether the dietary advice given during pregnancy actually leads to behavioural changes that reduce the future recurrence of GDM or the development of diabetes in the mother are unknown.
Also the influence of maternal diets on foetal programming and the future risk of childhood and adult obesity and diabetes are not fully understood.
PRECONCEPTION NUTRITIONAL COUNSELLING IN DIABETIC PREGNANCIES
All women attempting pregnancy should take a minimum of 400 mg folic acid supplements a day to prevent neural tube defects (8).
The higher dose of 5 mg folic acid a day is frequently recommended for diabetic women, despite any actual trial evidence for this, the rationale being that neural tube defects are commoner in this group.
In Britain, where the dietary folate intakes are relatively low despite numerous public health campaigns, less than 10% of women actually take folate supplements in early pregnancy (9).
The preconception period is a time when women with diabetes are encouraged to achieve the best glycaemic control possible.
Congenital malformations account for approximately 40% of all diabetic perinatal
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mortality, and can be significantly reduced when HbA1c levels are within the normal range.
To achieve this insulin regimens usually need to be intensified and many women with Type 2 diabetes will be started on insulin for the first time.
Dietetic input is required to build confidence, reduce hypoglycaemia and limit unnecessary weight gain (10).
Achieving near-normal glycaemic control is possible in most women with Type 2 and Type 1 diabetes.
However, in women with a long duration of Type 1 diabetes and significant autonomic neuropathy the risk of severe hypo- glycaemia is high.
Poor hypoglycaemia awareness and impaired counter- regulatory hormonal responses increase with the duration of Type 1 diabetes.
Dietary advice is essential to ensure adequate carbohydrate is being taken with each meal and that suitable low glycaemic carbohydrate snacks are being consumed between meals.
The preconception period is a good time to encourage weight loss and exercise in obese women with pre-existing Type 2 diabetes or a previous history of gestational diabetes.
Maternal obesity is independently associated with increased perinatal morbidity and mortality rates (11).
Epidemiological studies suggest that when obesity and diabetes coexist an adverse synergistic effect on pregnancy outcome occurs, including an unexplained increase in congenital malformation rates (12, 14).
Potentially a weight-reducing diet in obese women prior to conception will improve both glycaemic control and pregnancy outcome.
GENERAL DIETETIC ADVICE FOR PREGNANCY
Once pregnancy has been confirmed the diet should be reviewed to ensure the recommended vitamin and mineral intakes, including folate and iron, for pregnancy are met.
Ensuring adequate amounts of antioxidants in the diet may help to lessen the risk of pre-eclampsia and congenital malformation.
Recently dietary supplementation with the antioxidant vitamins C and E have been shown to reduce the incidence of pre-eclampsia in high-risk women (15).
Animal, but so far not human, studies have shown that these vitamins also protect embryos from the teratogenic effects of hyperglycaemia (16).
Calcium and vitamin D supplements during both pregnancy and lactation should be considered for Indian/Asian women and others with poor sunlight exposure or low calcium intakes (17,18).
Observational studies have linked low vitamin D levels with insulin resistance and diabetes (19,20) and, given the high incidence of diabetes among Asian women, ensuring adequate vitamin D in the diet seems prudent.
All women should be reminded of the dangers of excess alcohol (21), and the potentially harmful effects of uncooked meats and soft cheese.
THE DIETARY MANAGEMENT OF DIABETIC PREGNANCIES 95
RECOMMENDED MATERNAL WEIGHT GAINS IN NON-DIABETIC PREGNANCIES
Optimal weight gain for pregnancy needs to reflect the woman’s pre-pregnancy weight (22).
The guidelines on recommended maternal weight gains are based on large obstetric surveys in non-diabetic women in the United States (23).
The maternal weight gain required to minimise the frequency of small-for- gestational-age (SGA) infants is higher for underweight (BMI<19.8 kg/m2) than overweight or obese women, see Table 7.2.
As the majority of women with pre-existing Type 2 and GDM are already obese it is important that the dietary advice given does not result in higher post-partum than pre-pregnancy weights.
When the pre-pregnancy BMI is >35 kg/m2, the risk of a SGA infant is low and even when little or no maternal weight gain occurs the risk of a SGA infant does not appear to increase (11).
Overweight (BMI 26.1, 29 kg/m2) and obese (BMI >29 kg/m2) women are more likely to give birth to a LGA infant than normal weight women and this risk increases with increasing maternal weight gain.
The US obstetric recommendation for a minimum 7 kg weight gain for all obese women (23,24) may not be universally appropriate (11,25).
Nutritional advice given in pregnancy should include appropriate weight gain targets set in early pregnancy and based on pre-pregnancy weight.
ENERGY REQUIREMENTS IN PREGNANCY
Pregnancy is an anabolic state requiring energy for the products of conception, the foetal, placental unit and the increase in maternal tissues.
Newly synthesised maternal tissues account for a 15, 26% increase in metabolic rate in pregnancy (26).
The total calculated energy cost for pregnancy is around 355 640 kJ (85 000 kcal) and this translates into an extra 1191.3 kJ (285 kcal) a day (27,28).
These theoretical energy costs, originally derived in the 1960s by Hytten and Leitch, have been confirmed by more recent physiological measurements (29).
Maternal physiology is highly adaptable and pregnancy can progress during times of extreme food deprivation and/or physical activity (30).