Thyroid Disease

in PregnancyAshley Robbins, MD

Maternal Thyroid Physiology

Increased estrogen Increased TBG

Decreased free T4 and T3 H-P-T axis

stimulation

Increased Hcg Thyroid stimulation

Increased peripheral metabolism of T4

Trimester-specific reference

ranges for TSH

First trimester 0.1-2.5 mU/L

Second trimester 0.2-3.0 mU/L

Third trimester 0.3-3.0 mU/L

Placental-Fetal Thyroid

Physiology

Hypothalamic TRH – 8-9 wga

Active trapping of iodide – 12 wga

First indication of T4 production – 14 wga

Iodine uptake and T4 concentration

increases – 18-20 wga

Hyperthyroidism and

Pregnancy

0.2% of pregnancies

Heat intolerance, diaphoresis, fatigue,

anxiety, emotional lability, tachycardia,

wide pulse pressure

Weight loss, tachycardia > 100 bpm,

diffuse goiter

Hyperthyroid

Hyperthyroid at conception 25% rate of

SAB, 15% rate of premature delivery

Inadequately treated medically

indicated PTD & low birth weight

Inadequately treated thyrotoxicosis

PTD, perinatal mortality, severe

preeclampsia, heart failure, and perinatal

mortality

Graves’ Disease

95% of cases of hyperthyroid

Autoimmune disease mediated by

antiboides

Fetal thyroid can be stimulated or

inhibited

1-5% of neonates have hyperthyroid or

neonatal Graves from transplacental TSI

Neonatal Graves’ Disease

High fetal heart rate, fetal goiter,

advanced bone age, poor growth,

craniostynosis

Cardiac failure and hydrops with severe

disease

Monitor for signs of fetal thyrotoxicosis with

fetal heart rate and assessment of growth

Measure maternal TSHR-Ab in the 3rd TM

Treatment of Hyperthyroidism

Overt hyperthyroidism due to Graves’,

toxic adenoma, toxic multinodular goiter,

or gestational trophoblastic disease

Beta blocker for severe hyperthyroidism

and hyperadrenergic symptoms

Treat with thioamides- PTU or methimazole

Goal is to maintain free T4 in high-normal

range

Hypothyroidism and

Pregnancy

Fatigue, constipation, cold intolerance, muscle cramps, hair loss, dry skin

Overt hypothyroidism unusual (0.3-0.5%)

Anovulation

Increased risk of 1st TM loss

Hashimoto’s disease- most common cause in developed countries

Iodine deficiency- most common cause worldwide

Hypothyroidism and

Pregnancy

Preeclampsia and gestational HTN

Placental abruption

Nonreassuring fetal heart rate tracing

Preterm delivery

Low birth weight

Increased rate of C-section

Neuropsychological and cognitive impairment

Postpartum hemorrhage

Subclinical Hypothyroidism

Defined as elevated TSH when free T4 is in

the normal range

> 90% of hypothyroidism in pregnancy

Increased risk for severe preeclampsia,

preterm delivery, placental abruption,

and/or pregnancy loss

Universal screening??

Observational studies- testing only high-

risk will miss up to 1/3 with subclinical or

overt hypothyroid

Prospective studies- universal screening

did not improve pregnancy outcomes

Targeted Case-finding

Screening

Screen with TSH if: Symptomatic

From area of known moderate-severe iodine insufficiency

Family or personal history of thyroid disease

Personal history of TPO antibodies

Type 1 diabetes

History of Pre-term delivery or miscarriage

History of head or neck radiation

Morbid obesity

Infertility Age>30 y/o

Targeted Case-finding

Screening

Check TSH first trimester

If abnormal check free T4

If TSH > 2.5 & free T4 normal, check TPO

antibodies

Helpful in making treatment decisions in

those with borderline thyroid studies

Helps predict postpartum thyroid

dysfunction

Treatment of Hypothyroid

All women with overt and subclinical

hypothyroid

Moderate-severe overt hypothyroid- start

with Levothyroxine 1.6 mcg/kg/day

TSH < 10- 1 mcg/kg/day

Taken on an empty stomach, ideally 1 hr.

before breakfast

Reevaluate serum TSH in 4 weeks

Treatment of Preexisting

Hypothyroid

Requirements for thyroid hormone

increase as early as the 5th week of

gestation

Check TSH when pregnancy established

OR preemptively increase Levothyroxine

by about 30% (double daily dose 2 days

per week)

Check TSH every 4 weeks until normal

Postpartum Thyroiditis 5-10 % of women in the USA

Occurs after normal delivery and pregnancy loss

“Classic” presentation Transient hyperthyroid phase of 6 weeks – 6

months after delivery

Hypothyroid phase follows and lasts up to 1 year

Most presents with hyperthyroid or hypothyroid alone

Autoimmune disorder (increased incidence with Type 1 diabetes)

Postpartum Thyroiditis-

Hyperthyroid Phase

Fatigue, palpitations, heat intolerance,

and nervousness

Limited duration

Beta blockers may reduce symptoms

No role for antithyroid medications

Postpartum Thyroiditis-

Hypothyroid Phase

Fatigue, hair loss, depression, impairment

of concentration, and dry skin

Usually requires treatment

Wean off therapy 6 months after initiation

OR continue therapy until finished with

childbearing

Summary Points

Trimester-specific thyroid function tests

Graves’ disease most common cause of

hyperthyroid and is mediated by production

of antibodies

Targeted screening for hypothyroid is

recommended

T4 requirement increases as early as 5 wga

Postpartum thyroiditis occurs in 5-10% of

women

Thank you