Treatment of Hypothyroidism During Pregnancy
Both clinical (overt) hypothyroidism and subclinical hypothyroidism should be treated during pregnancy regardless of severity to prevent adverse maternal and fetal outcomes. 1
Definitions and Diagnostic Criteria
- Overt hypothyroidism is characterized by elevated TSH with decreased free T4 levels 1
- Subclinical hypothyroidism is identified by elevated TSH with normal free T4 levels in an asymptomatic pregnant woman 1
- TSH testing using monoclonal antibodies is the recommended initial screening test for suspected thyroid disease in pregnancy 1
Risks of Untreated Hypothyroidism in Pregnancy
Maternal Risks:
- Increased risk of preeclampsia 1
- Higher rates of preterm delivery 1, 2
- Pregnancy-induced hypertension (occurs in 22-44% of women with untreated hypothyroidism) 3
- Placental abruption 1
Fetal/Neonatal Risks:
- Low birth weight 1
- Fetal death 1, 2
- Congenital cretinism (with iodine deficiency) 1
- Cognitive impairment in children (especially with first trimester hypothyroidism) 1, 3
- Impaired neuropsychological development 1
Treatment Recommendations
- All pregnant women with overt hypothyroidism require treatment 4
- All pregnant women with subclinical hypothyroidism (regardless of TSH level) should be treated 4
- Women planning pregnancy with hypothyroidism should be treated before conception with a target TSH of 1 mU/L 5
- Levothyroxine is the treatment of choice for hypothyroidism during pregnancy 1, 3
Medication Management
- Women already on thyroid replacement therapy often need dose increases by 4-6 weeks gestation 1
- Dose increases typically range from 25-50% during the first trimester 5
- Monitor thyroid function with TSH and free T4 or FTI every 2-4 weeks during pregnancy to guide dosage adjustments 6
- The goal is to maintain TSH in the normal range and free T4 in the high-normal range 1, 5
Special Considerations
- Women with positive thyroid antibodies (TPO-ab) have double the risk of miscarriage and may develop postpartum thyroiditis 3
- Adequate treatment eliminates or significantly reduces the risks of complications 3, 2
- After delivery, levothyroxine requirements typically decrease to pre-pregnancy levels 3
Monitoring Protocol
- Screen high-risk women before or during early pregnancy (those with previous thyroid disease, type 1 diabetes, or family history of thyroid disorders) 3, 7
- Perform TSH and free T4 testing in pregnant women with suspected hypothyroidism 1
- Monitor TSH every trimester in treated women to ensure stable thyroid function 6
Key Pitfalls to Avoid
- Delaying treatment of subclinical hypothyroidism in pregnancy (even mild cases should be treated) 1, 4
- Inadequate dose adjustments during pregnancy (requirements often increase) 5, 3
- Failure to monitor thyroid function regularly during pregnancy 6
- Overlooking hypothyroidism in women with nonspecific symptoms that may be attributed to normal pregnancy 2