overt hypothyroidism complicates up to 3 of 1,000 pregnancies subclinical hypothyroidism is...
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Overt hypothyroidism complicates up to 3 of 1,000 pregnancies
Subclinical hypothyroidism is estimated to be 2-5 % (Canaris GH, 2000)
In Macau, around 2-3% (rough estimation)
Epidemiology
Control of Thyroid FunctionHypothalamus releases TRH
Act on the pituitary gland to release TSH
TSH causes the thyroid gland to release the thyroid hormones (T3 and T4)
TRH and TSH concentrations are inversely related to T3 and T4 concentrations.
•99% circulating T3 and T4 is bound to TBG. 1% free form Biologically
Active
Clinical Hypothyroidism
Subclinical Hypothyroidism
TSH High (>10) High (>3 - <10)
Free T4 Low Normal
Free T3 Normal or low Normal
Clinical / Subclinical Hypothyroidism• Serum TSH level > 3.0 mIU/l• Subclinical hypothyroidism elevated TSH with normal FT4, FT3.
Primary hypothyroidism Secondary/tertiary hypothyroidism Iatrogenic Environmental
Types of Hypothyroidism
Affect 38% of worldwide population (Pearce EN, 2008)
Sources: Iodized salt and seafood. Others: cow milk, egg, beans…
Perinatal mortality Congenital cretinism (growth failure, mental
retardation, other neuropsychological deficits)
Average intake 250 µg/d Urine iodine > 150 µg/d Diana L. Fitzaptrick 2007
Iodine Deficiency
Elevated TSH (> 3.0 mIU/l) with normal FT4, FT3.
31 % with anti-TPO antibody (Casey BM, 2007)
More common on women with autoimmune diseases
50 % hypothyroidism in 8 years May cause childhood IQ decrease Increase in preterm 4% vs 2.5% in euthyroid
mother (Casey BM, 2007)
Subclinical Hypothyroidism
<1% hypothyroidism cases
Low or normal serum TSH concentrations + low serum T4 and T3
2nd (TSH deficiency) hypothyroidism: - pituitary tumor - postpartum pituitary necrosis (Sheehan's syndrome) - trauma, infiltrative diseases.
3rd (TRH deficiency) hypothyroidism can be caused by - Damages the hypothalamus or - Interferes with hypothalamic-pituitary portal blood flow
Secondary and Tertiary Hypothyroidism
Slowing of metabolic processes:Lethargy/fatigue weight gain cognitive dysfunctioncold intolerance constipation bradycardiadelayed relaxation of tendon reflexesslow movement and slow speech
Deposition of matrix substances:Dry skin hoarseness edemapuffy face and eyebrow loss peri-orbital edemaenlargement of the tongue
OthersDecreased hearing myalgia and paresthesia depressionmenorrhagia arthralgia pubertal delaygalactorrhea
Symptoms of Hypothyroidism
Symptoms Hypothyroidism Pregnancy
Fatigue
Constipation
Hair Loss
Dry Skin
Brittle Nail
Weight Gain
Fluid Retention
Bradycardia
Carpel Tunnel Syndrome
Overlapping Complaints
Pregnancy is a state of relative iodine deficiency, because:
- Active transport to fetoplacental unit - Increase iodine excretion in urine, 2 fold (increased GFT & decreased renal tubular reabsorption)
- Thyroid gland increases its uptake from the blood
Physiologic Changes in Pregnancy
TBG
TT4 & TT3
FT4 & FT3 (crosses the placenta in the 1st half of pregnancy)
TSH (does not cross placenta)
Overt hypothyroidism in pregnancy is rare
In continuing pregnancies hypothyroidism is associated with increased risk of:
◦ Pre-eclampsia◦ Placenta Abruption◦ increased c-section rates◦ Fetal death (especially if increased TSH occurs
in 2nd trimester) Motherisk April 2007
Maternal thyroid hormones are important in embryogenesis
No production until 12 weeks, therefore needs mom’s T4 for fetal brain development
Maternal hypothyroidism can cause negative effect on fetal intellectual development.
Higher incidence of LBW (due to medically indicated preterm delivery, pre-eclampsia, abruption)
Iodine deficient hypothyroidism -> congenital cretinism (growth failure, mental retardation, other neuropsychological deficits)
Motherisk April 2007, CMAJ Apr 2007 176(8)
More for the Baby!!
Treatment before 10 weeks’ gestation No adverse effect
Family Hx of autoimmune thyroid disease Women on thyroid therapy Presence of goiter or thyroid nodules Hx of thyroid surgery Infertility Unexplained anemia or hyponatremia or high
cholesterol level Previous Hx of - neck radiation - postpartum thyroid dysfunction - previous birth of infant with thyroid problem Other autoimmune chronic conditions: Type 1 DM
Indications for Screening universal screening is not recommended (ACOG)
Overt hypothyroidism: symptomatic patient elevated TSH level low levels of FT4 and FT3
Subclinical hypothyroidism: asymptomatic patient elevated TSH normal FT4 and FT3
Laboratory Workup
Replacement with external thyroid hormone -- levothyroxine (Levothyroid, Levoxyl, Synthroid, and Unithroid).
Levothyroxine (Synthroid) pregnancy category A
◦ A sterioisomer of physiologic thyroxine◦ 1.6 mcg/kg, ◦ usually about 50 to 100 mcg/day for women◦ 30-60 minutes before eating breakfast.
Treatment
The American Association of Clinical Endocrinologists recommends keeping the thyroid-stimulating hormone (TSH) level between 0.3 and 3.0 mIU/L.
After readjustment of levothyroxine, observe 6-8 weeks
Check TSH every trimester
Treatment and Goals
Rapid or irregular heartbeat Chest pain or shortness of breath Muscle weakness Nervousness Irritability Sleeplessness Tremors Change in appetite Weight loss
Side Effects of Synthroid
Safe in pregnancy and lactation Very little thyroxin crosses the placenta NO risk of thyrotoxicosis of fetus
Patients who were on thyroxine therapy before pregnancy should increase the dose by 30% once pregnancy is confirmed (Bombrys et al, 2008)
Keep TSH level between 0.3 and 3.0 mU/L.
TSH should be monitored every trimester until delivery.
Pearls