Graves disease during pregnancy

By trimester

Weeks 1–13

1st trimester

First-trimester care leans toward propylthiouracil over methimazole when medication is needed, based on guidance from the FDA, ACOG, and the American Thyroid Association, and this is also when a baseline TSH-receptor antibody (TRAb) level is typically drawn to gauge risk to the baby later on.

Weeks 14–27

2nd trimester

By 18 to 20 weeks, monthly fetal ultrasound is the guideline-recommended step once maternal TRAb crosses an actionable level, since this is roughly when the fetal thyroid begins responding to these antibodies; repeat antibody testing around 18 to 22 weeks helps confirm whether that closer monitoring is still needed.

Weeks 28–birth

3rd trimester

In the third trimester, antibody levels are often repeated again around 30 to 34 weeks, and Graves activity can shift as pregnancy goes on, so the medication plan and monitoring frequency are revisited rather than left unchanged from earlier in pregnancy.

What does the evidence show for graves disease?

• Graves disease involves an antibody called thyroid stimulating immunoglobulin, or TSI, which causes the thyroid to make too much thyroid hormone. Rarely, when TSI levels are high, this same antibody can travel to a baby's bloodstream and cause the baby's own thyroid to become overactive too, not just the parent's. 1
• An overactive thyroid in a newborn can lead to a fast heart rate that progresses to heart failure, early closing of the soft spot in the baby's skull, poor weight gain, and irritability, a distinct set of newborn complications tied specifically to antibody-mediated Graves disease rather than to hyperthyroidism in general. 1
• TSI antibodies can persist even after the thyroid itself has been destroyed by radioactive iodine or removed by surgery, which is why a pregnancy care team needs to know about a Graves disease history regardless of how it was previously managed, not only when someone is currently taking thyroid medication. 1
• Transplacental passage of maternal TSH-receptor antibodies can cause fetal hyperthyroidism as early as 20 weeks of gestation, which is why guidelines commonly recommend monthly fetal ultrasound starting at 18 to 20 weeks; over 95% of neonatal Graves disease cases occur when maternal antibody levels exceed roughly 5 IU/L, about three times the usual upper limit of normal for that measurement. 2
• Newborn thyroid assessment commonly starts with a cord blood sample at birth, followed by thyroid function testing between days 3 and 5 of life, with repeat testing between days 10 and 14 if the mother's antibody status was positive or unknown, giving a concrete testing schedule rather than a single one-time check. 2
• A multicenter study of 500 women with a history of Graves disease across 44 Dutch centers found trimester-specific antibody thresholds, roughly 27 IU/L in the first trimester, 21 IU/L in the second, and 7 IU/L in the third, below which no cases of fetal or neonatal hyperthyroidism occurred, figures notably higher than the uniform threshold used in some current guidelines. 3
• In that same study, every case of fetal or neonatal hyperthyroidism among women with a history of Graves disease occurred in those who had previously had radioactive iodine care, singling out that particular subgroup for closer attention even when current disease activity looks low. 3
• The FDA, ACOG, and the American Thyroid Association have indicated that propylthiouracil might be preferred over methimazole for hyperthyroidism specifically in the first trimester, while the FDA separately warns that propylthiouracil itself can cause serious liver injury in people who take it, including pregnant women; either way, a baby's thyroid level should be checked after delivery if the parent took propylthiouracil or has Graves disease. 4

When should I call my provider about graves disease?

A newborn with antibody-driven thyroid overactivity from Graves disease can develop a fast heart rate that progresses to heart failure, early closing of the soft spot in the skull, poor weight gain, or irritability, which is why any baby born to a parent with current or past Graves disease needs its thyroid checked rather than being assumed unaffected. For the pregnant parent, a racing or irregular heartbeat together with chest pain, fainting, or severe shortness of breath needs emergency evaluation, since these can point to a thyroid-related cardiac crisis rather than an ordinary pregnancy symptom. Trust your read on your own body. If something feels off beyond the list above, please consult your healthcare provider rather than waiting it out.