Detection of gestational diabetes

Routine screening of all pregnant women for hyperglycaemia should no longer be considered controversial as two large RCTs have both shown benefit from treating gestational diabetes and the results from the Hyperglycaemia and Adverse Pregnancy Outcome study (HAPO) are being used to define the diagnostic criteria that predict an adverse perinatal outcome. The two currently most widely used criteria are detailed in Table 16.1.

Women who are more likely to develop gestational diabetes are those who have a previous history of gestational diabetes; who suffered an intra-uterine death late in pregnancy; who have a close family member or members who are diabetic; who are from an ethnic group with a high prevalence of type 2 diabetes; who are older than 30 years, who have persistent glycosuria, or where there is fetal macrosomia should be tested early in pregnancy, ideally before they conceive. If the test is negative they should be retested at the beginning of the third trimester when all women should be screened.

Management of diabetes

Timing of delivery

Most diabetic women whose diabetes is well controlled will be able to continue their pregnancy to full term. If metabolic control has been inadequate and polyhydramnios or fetal macrosomia is present, delivery by 38 weeks is indicated.

Management of labour

Labour can be induced in the usual way, and the fetus monitored as for any high-risk pregnancy. Blood glucose levels need to be monitored at frequent intervals and, if necessary, an infusion of short-acting insulin can be given. The fetus should be monitored throughout labour. During vaginal delivery shoulder dystocia should be anticipated.

The risk of shoulder dystocia is 14% if the birthweight is between 4000 and 4500 g (twice that for the offspring of non-diabetic women) and 52% for birthweights greater than 4500 g (three times greater); consequently, elective caesarean section is recommended if the estimated fetal weight is more than 4000 g. A caesarean section may be performed if there is significant macrosomia or non-reassuring fetal status, or if labour fails to progress satisfactorily. Uncomplicated diabetes is not an indication for operative delivery.

As maternal insulin requirements quickly return to prepregnancy levels after delivery, monitoring of blood glucose levels is important.

The newborn baby

Following delivery the baby (Fig. 16.1) should be carefully assessed by a neonatologist. Early feeding with oral glucose if necessary is important to minimize the risk of neonatal hypoglycaemia. The blood glucose levels should be monitored before each feed for the following 2 days. If hypoglycaemia persists the baby may require enteral feeding or intravenous glucose or glucagon.

Fig. 16.1 Newborn baby of a diabetic mother.

Babies of diabetic mothers who had difficulty controlling their blood glucose during pregnancy are likely to have poor temperature control, to feed slowly, and to be jaundiced, hypocalcaemic and hypomagnesaemic. If these babies are born before term they are more likely to develop the respiratory distress syndrome because there is delayed resorption of lung fluid, which causes transient tachypnoea in the newborn baby.

Later in life these babies are at risk of developing abnormal glucose tolerance and obesity, particularly if the mother’s diabetic control has been suboptimal.

Follow-up of women who have had gestational diabetes

Follow-up is important as up to 50% of women with gestational diabetes may develop overt diabetes, usually type 2, and if this is detected early there is an opportunity to minimize the development of the complications of diabetes. Regular testing for hyperglycaemia should be performed, at least every 2 years if the GTT is normal and they are of child-bearing age, thereafter every 3 years, and every year if there is impaired fasting or impaired glucose tolerance.

At these follow-up visits women who have had gestational diabetes can be encouraged to follow a diet appropriate for a diabetic, avoiding refined carbohydrates and ensuring adequate dietary fibre. Because of the risk of developing diabetes they should be advised to take the following measures:

These women should also be reminded that they have a 50% chance of developing gestational diabetes in a future pregnancy. If the woman is intending to become pregnant again, testing for hyperglycaemia immediately before conception is recommended. Otherwise, testing should be done as soon as possible in early pregnancy.

Autoimmune hyperthyroidism (Graves’ disease)

Autoimmune hyperthyroidism (Graves’ disease) may precede pregnancy or may arise in pregnancy because of the hypermetabolic state of the mother. Untreated hyperthyroidism carries an increased risk of premature delivery (10–25%), growth restriction and fetal death (8–15%). In pregnancy, treatment with propylthiouracil (starting with 100 mg 8-hourly and titrating according to thyroid-stimulating hormone (TSH) and T₄ levels and clinical symptoms) is preferred as it inhibits thyroxine synthesis and the peripheral conversion of T₄ to T₃. It does cross the placenta, and so consequently the objective is to maintain the free T₄ index in the normal range so that the fetus does not become hypothyroid. Ultrasound examination of the fetus is used to assess fetal heart rate, goitre and growth particularly if the mother remains hyperthyroid. Labour is usually uneventful and a thyroid storm is rarely seen in pregnancy. About 10% of neonates become thyrotoxic in the neonatal period because of the transplacental passage of thyroid-stimulating immunoglobulins. Affected babies can be identified during pregnancy by measuring the level of maternal TSH receptor antibody in the last trimester.

Parenchymatous (colloid) goitre

Although the mother’s thyroid gland enlarges in pregnancy, it is uncommon for it to cause symptoms. The cause of the goitre is partly due to decreased absorption of iodine in the first half of pregnancy. A pregnant woman should take iodized table salt to prevent the fetus developing colloid goitre.

Hypothyroidism

The most common causes of hypothyroidism in women in the reproductive age group are Hashimoto’s thyroiditis, surgery (thyroidectomy) and radiotherapy for thyroid carcinoma. Also at risk are women with other autoimmune diseases such as type 1 diabetes. Inadequately treated hypothyroidism increases the risk of infertility, pre-eclampsia, growth restriction, premature birth, placental abruption and fetal death. In early pregnancy an increased need for thyroxine occurs that is associated with a rise in T₃ and T₄, which plateaus at about the 30th week. In women with hypothyroidism this rise cannot occur, and these women need more thyroxine than when not pregnant. The preferred replacement is the pure T₄ preparation levothyroxine. The extra quantity needed can be estimated from the serum thyroid-stimulating hormone (TSH, or thyrotrophin) level, a fall indicating a need for more thyroxine, above the average daily dose of 100 μg, as required. The compliance of the patient should be ensured, as insufficient thyroxine may increase maternal and fetal morbidity.

Prolactin-secreting adenomas

Women with known macroadenomas should be treated with surgery or radiation before becoming pregnant, as up to 33% develop symptoms during pregnancy (headaches, visual field defects) if untreated. Microadenomas rarely (5%) cause symptoms, and if enlargement is detected this can be treated with bromocriptine. There are no particular complications associated with labour, and breastfeeding is not contraindicated.

Diabetes insipidus

This disorder is rarely encountered in pregnancy and the treatment is synthetic vasopressin (DDAVP) administered intranasally. Oxytocin release is independent of vasopressin secretion, and thus labour and lactation are not usually affected by the condition.

Cushing syndrome

Women with untreated Cushing syndrome are usually infertile owing to the inhibition of gonadotrophin release by the excess androgen secretion. Pregnancies in women with treated Cushing syndrome are complicated by an increased risk of preterm delivery and hypertension (both up to 66%) and perinatal deaths (7%). These complications appear to be more common with adrenal adenomas than with hyperplasia. Non-suppressible tumours may need to be treated surgically, and this is associated with an improved pregnancy outcome.

Addison disease

In treated women the pregnancy is usually uneventful, replacement therapy is given with cortisone acetate and fludrocortisone acetate, and additional doses are required during the stress of labour and delivery.

Phaeochromocytoma

This may present in pregnancy as a hypertensive crisis or as severe pre-eclampsia. Diagnosis is made by detecting elevated catecholamines in a 24-hour urine collection. If detected before 24 weeks surgical excision is usually performed; after this time, phenoxybenzamine is used to achieve stabilization, with delivery by caesarean section when fetal maturity is assured, to avoid the excessive catecholamine release associated with labour.