Thyroid Disease in Pregnancy Flashcards
General
Definition
Thyroid hormone dysregulation during pregnancy
Epidemiology
Thyroid disease is common in women of childbearing age
Hypothyroidism
- Occurs in 1% of pregnancies
- COMMONEST cause worldwide is iodine deficiency (often diet related)
- Hashimoto’s thyroiditis is also very common
Hyperthyroidism
- Autoimmune Graves’ disease and subsequent thyrotoxicosis affects 2 per 1,000 pregnancies
- Usually diagnosed before pregnancy
Aetiology
Physiological changes of pregnancy include:
- Plasma volume expansion
- Increased thyroid binding globulin
- Relative iodine deficiency
NOTE: hCG is structurally similar to TSH and so can act on the TSH receptor to produce increased thyroid hormone
1st trimester: fall in TSH and rise in free T4 is expected ( free T4 will then fall with advancing gestation)
IMPORTANT: the foetus does not have a functioning thyroid until 14-16 weeks
Hypothyroidism
- Iodine deficiency
- Hashimoto’s thyroiditis
- Post-ablative therapy or surgery
- Transient thyroiditis
- Thyroid infiltrative disorders
- Congenital hypothyroidism
- Pituitary or hypothalamic dysfunction- tumours, surgery, Sheehan’s, drugs
Hyperthyroidism
- Autoimmune Graves’ disease
Other causes of hyperthyroidism (5%) include:
- Toxic multinodular goitre
- Toxic thyroid adenoma
- Subacute thyroiditis
- Pituitary adenoma
- High concentrations of hCG
- Iodine- may suppress TSH (found in Kelp supplements)
- Struma ovarii – ovarian teratoma producing ectopic thyroxine
- Thyroid cancer metastases
Risk factors
Hypothyroidism
- Family history of thyroid disease
- Personal or family history of autoimmune disease - T1DM, Coeliac disease, Pernicious anaemia
- History of Turner’s or Down’s syndrome
- History of iodine deficiency
- Previous radiotherapy to head and neck, radioiodine treatment or thyroid and neck surgery
Hyperthyroidism
- Females
- Family history
- Smoking
- Low iodine intake
- Autoimmune disease
Symptoms
EXAGGERATED SYMPTOMS OF PREGNANCY
Hypothyroidism
- Cold intolerance
- Weight gain
- Constipation
- Low mood
- Tired
- Muscle cramps
Hyperthyroidism
- Heat intolerance
- Fatigue
- Palpitations
- Tremor
- Insomnia
- Weight loss
- Sweating
- Anxious
Signs O/E
- Goitre
- Hyperactivity
- Exophthalmos, Pretibial myxoedema
- Pale
- Brady/ tachycardia
- Hypertension with wide pulse pressure
- Hyperemesis gravidarum
Investigations
Basic observations, urine dipstick
TFTs- Free T4, fT3 AND TSH- ALL should be used
- There is a fall in TSH and rise in fT4 concentrations in the 1st trimester of pregnancy followed by a fall in fT4 with advancing gestation
HbA1c, Coeliac serology, FBC and serum B12 level, serum lipids
Serum TSH-receptor antibodies- if current or previous history of Graves’ disease
ECG (more for ruling out differentials)
Screening at booking (perform TFTs on…)
- Current thyroid disease
- Previous thyroid disease
- 1st degree FHx of thyroid disease
- AI conditions (Coeliac’s, T1/T2DM, GDM)
Management
HYPOTHYROIDISM
MEDICAL
1st Line: Levothyroxine
- Women should start/ continue with thyroid replacement therapy during pregnancy
- If diagnosed pre-pregnancy, should start this ASAP as there is an increased demand for thyroxine during pregnancy (foetus needs this as cannot make its own)
- Increase dose by 25mg- if known thyroid disease and as soon as pregnancy confirmed (even if currently euthyroid)
- Repeat TFTs in 2 weeks and perform in each trimester to adjust dose if required
- This hopes to mimic the rise in thyroid hormone seen in normal pregnancy
AIM: Biochemical euthyroidism (TSH < 4mmol/L)
MONITORING
- TFTs performed every 2-4 weeks to ensure biochemical euthyroidism
- More often if dose adjustments are required
- Maternal T4 levels are extremely important in 1st trimester as suboptimal replacement therapy is associated with developmental delay and pregnancy loss
POSTPARTUM
- Discuss with Endocrinologist about changes to Levothyroxine dose
- Levothyroxine dose should be reduced to pre-pregnancy levels in most women
- Check serum TSH levels after 6 weeks
HYPERTHYROIDISM
MEDICAL (NO SURGERY)
- Treat @ lowest acceptable dose due to SE of foetal hypothyroidism
- 1st line: Propylthiouracil
- (1st trimester)
- This does NOT cross the placenta.
- However, it can lead to urinary abnormalities, particularly in male foetuses
- May also lead to decompensated liver failure in the mother (hepatotoxicity)
1st line: Carbimazole
(2nd and 3rd trimesyer)
- This crosses the placenta and can affect the foetus
- May cause neurological and cardiovascular abnormalities
- Most commonly, aplasia acutis is seen- where there is an area of the baby’s head that never grows any hair.
IMPORTANT: often give 20mg, then step down to 15mg and 10mg.
IMPORTANT: radioactive iodine is CONTRAINDICATED in pregnancy as obliterates foetal thyroid
MONITORING
33% of women can actually stop treatment during pregnancy
- TFTs performed every 2-4 weeks to ensure biochemical euthyroidism
- Maternal WCCs- both drugs can cause agranulocytosis so need to regularly check
- LFTs- monthly if on PTU due to maternal hepatotoxicity
POSTPARTUM
- TFTs should be checked after delivery
- Doses of meds usually require readjustment postpartum to prevent relapse
- Check serum TSH and fT4 levels 6-8 weeks postpartum
Complications
Complications
Hypothyroidism
- Cardiovascular: dyslipidaemia, metabolic syndrome, CHD and stroke, heart failure
Increased risk of:
- Miscarriage
- Anaemia
- Pre-eclampsia
- Placental abruption
- PPH
- Stillbirth
Myxoedema coma- lethargy, bradycardia, hypothermia, seizures and/or coma
Neurological and cognitive impairment
Foetal:
- Cretinism
- Cognitive deficits
- Hydrops (foetal cardiac failure)
Hyperthyroidism
- Graves’ orbitopathy
- Thyrotoxic crisis- LIFE THREATENING
In uncontrolled pregnancy, there is increased risk of:
- Miscarriage
- Pregnancy-induced hypertension
- Maternal heart failure
- Preterm delivery
- IUGR
- Low birthweight
- Foetal goitre
- Foetal hydrops and heart failure
- Foetal or neonatal thyrotoxicosis
- Foetal death
NOTE: If there is foetal compromise, can give PTU or flecainide to help reduce baby’s HR
Compression symptoms- dysphagia, breathlessness
Cardiovascular: AF, heart failure
Reduced bone mineral density and osteoporosis
Post-partum thyroiditis (PPT)
There are THREE stages:
- Thyrotoxicosis
- Hypothyroidism
- Normal thyroid function (but high recurrence rate in future pregnancies)
Investigate: using TFTs ONLY
NOTE: TPO antibodies are found in 90% of patients- do NOT test for these
Diagnosis:
- Patient within 12 months of giving birth
- Clinical manifestations suggestive of hypothyroidism
- TFTs support diagnosis
- Initial TFTs show a thyrotoxic pattern
- Check TFTs 4-8 weeks after resolution of thyrotoxic phase to screen for hypothyroid phase (or sooner of symptoms develop)
- Do NOT treat thyrotoxic phase as the thyroid is NOT overactive
Propranolol may be used for symptom control
If TFTs show a hypothyroid pattern, discuss starting Levothyroxine.
In general:
- Women breast feeding or planning another pregnancy should be started
- Untreated asymptomatic women who are not planning a pregnancy should be reassessed in 4-8 weeks- if the TSH remains above the reference range, may start on Levothyroxine
- Untreated asymptomatic women should have their TFTs checked every 4-8 weeks until thyroid function normalises
Annual TFT monitoring once resolves
Prognosis
Corrected hypothyroidism does not influence pregnancy outcome or complications but suboptimal replacement is associated with developmental delay and preg loss
Hyperparathyroidism
Parathyroidectomy may be indicated for severe cases
o Mild hyperparathyroidism is managed with adequate hydration and low calcium diet
o Risks:
- Increased rates of miscarriage Intrauterine death
- Preterm labour Neonatal tetany
Hypoparathyroidism
Risks:
- Increased risk of 2nd trimester miscarriage
- Foetal hypocalcaemia
- Neonatal rickets
Management:
- Vitamin D
- Oral calcium supplements
- Regular monitoring of calcium and albumin
