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
Top Related