When Mum Has Graves' Disease: How Doctors Work Out Which Babies Need Thyroid Checks, and Why Some Need Them for Longer

A family guide to three 2026 studies from the Netherlands, Australia and Japan (Saleh et al., Pathmanathan et al. and Adachi et al.) on antibody tests in pregnancy, checking babies after birth, and caring for babies who need treatment

Mothers who have, or used to have, Graves' disease carry antibodies that can cross the placenta and briefly over-stimulate their baby's thyroid gland. Three 2026 studies show that a blood test in pregnancy can pick out the small number of babies at real risk, that hospitals do not always complete the checks babies need after birth, and that a few babies who need treatment also need thyroid checks for some months afterwards.

If you are pregnant and have Graves' disease, or had it treated years ago, you may have been told that your baby will need extra blood tests after birth. That can be worrying, especially when the reasons are not fully explained. The good news is that most babies are not affected at all. This article explains why the checks exist, what new research from the Netherlands, Australia and Japan found [1][2][3], and what it may mean for your baby.

What Graves' disease is and how it can reach the baby

The thyroid is a small gland in the neck that makes hormones controlling how fast the body runs. In Graves' disease, the immune system makes antibodies, a kind of protein normally used to fight infection, that switch the thyroid on too strongly. Doctors call them TSH-receptor antibodies, or TRAb, because they attach to the same spot on the thyroid as TSH (thyroid-stimulating hormone), the brain's own "go" signal to the gland. These antibodies can cross the placenta, so a baby can be affected before and after birth [4][5]. Some antibodies do the opposite and block the thyroid, which can make a baby's thyroid under-active instead.

An important point is that the antibodies can remain in the mother's blood even after her own thyroid has been treated with surgery or radioactive iodine, so a mother can feel completely well and still pass them on [5][6]. The antithyroid medicines some mothers take also cross the placenta [7]. They help protect the baby in the womb [5], but after birth they wash out of the baby's body, which is why some babies only show signs of an over-active thyroid a week or so after they are born [1].

How families and doctors have handled this until now

Doctors have known about this problem for a long time. Over 40 years ago, specialists reported that babies with an over-active thyroid at birth sometimes had learning difficulties or early fusion of skull bones later in childhood [8]. Others noticed that some babies with an over-active thyroid around birth, or exposed to high thyroid hormone levels in the womb, were later left with a thyroid that was too sluggish, because the brain's control centre had been "turned down" [9][10]. European experts published advice on testing mothers' antibodies in pregnancy as early as 1998 [11].

Over the following years, studies in France and elsewhere suggested a practical plan. Mothers would have their antibody level checked in pregnancy; if it was raised, the baby's umbilical cord blood would be tested at birth, and the baby would have thyroid blood tests around days 3 to 5 and again around days 10 to 14 [12][13]. A low TSH level in a baby's first week turned out to be a useful warning sign [14]. But one question was never settled: how high does the mother's antibody level need to be before doctors should worry? Different guidelines gave different answers, often expressed as "a few times above the normal limit" [15][16]. The trouble is that different laboratories use different testing kits, and these kits can give quite different numbers for the same blood sample [17]. A 2024 review of the research also concluded that hospitals needed clearer, more consistent plans [18].

Three studies, three questions

The three new studies each look at a different step on the baby's journey.

The first, from the Netherlands, followed 678 pregnancies at 44 hospitals between 2010 and 2023 and measured the mothers' antibody levels in each third of pregnancy (each trimester) using one specific laboratory test [1]. It asked: at what level does a baby become at risk?

The second, from a large specialist maternity hospital in Queensland, Australia (the paper does not name it), looked back at the records of 70 mothers with Graves' disease who gave birth between 2018 and 2022 [2]. It asked: did babies actually get the checks the hospital's own plan said they should?

The third, from Japan, described 12 newborns with Graves' disease who needed medicine, cared for between 2012 and 2021 by a Tokyo-based children's hormone team and the newborn units it works with [3]. It asked: what happens to these babies, and which early clues predict how they will do?

What the Dutch study found: the safe range is wider than thought

Among 500 pregnancies in women whose Graves' disease had been treated in the past, 13 babies (about 1 in 38) had a thyroid problem caused by the antibodies [1]. Among 178 pregnancies in women with active disease, 12 babies (about 1 in 15) were affected.

For mothers with past Graves' disease, the study found clear "safe" levels on its particular test: no baby was affected when the mother's level was below 27 units in the first trimester, 21 in the second or 7 in the third [1]. In the first trimester, for example, none of 325 mothers below that level had an affected baby. All 13 affected babies in this group were born to mothers who had been treated with radioactive iodine before pregnancy, which fits earlier research showing antibodies can stay high for years after that treatment [19].

These safe levels are much higher than the cut-off most guidelines use. Using the usual guideline cut-off would have flagged 75 of the 500 pregnancies as at risk, compared with 16 using the new first-trimester level, meaning many more scans and blood tests for families whose babies were never at risk [1]. The researchers stress that these numbers only apply to the one laboratory test they used, so your own hospital's numbers may be different.

For mothers taking antithyroid medicine during pregnancy, the picture was less tidy. A few babies were affected even when the mother's level was low, and all of their mothers were taking antithyroid medicine. In this group, problems often showed up only after birth, once the medicine had worn off [1]. For these babies, the researchers advise checking after birth whatever the antibody level.

What the Australian study found: good plans are not always followed

The Queensland hospital had a sensible written plan. Twenty babies, from 18 pregnancies (there were two sets of twins), were in the at-risk group [2]. But only 2 of those 20 babies had the recommended antibody test on their cord blood, and only 2 of 20 received every step of the planned follow-up. Thirteen had the day 3 to 5 blood test. Of the two babies who were tested properly, one did have an over-active thyroid and was treated at a children's hospital. Two babies had neither of the planned thyroid blood tests.

The authors found the reasons were mostly practical: cord blood results took a long time, it was unclear whose job each step was, notes were inconsistent, and staff were unsure about the different antibody tests [2]. They recommend clearer rules, better record-keeping, staff training and repeat checks of how well the plan is working. A similar story about thyroid follow-up in premature babies is told in our article on two Australasian screening audits.

What the Japanese study found: some babies need checks for longer

All 12 babies in the Japanese study were treated, most with a medicine called methimazole that calms the thyroid, usually alongside an iodine medicine that also calms the thyroid, and sometimes with a medicine to settle a fast heartbeat [3]. Methimazole treatment lasted between about 3 weeks and 6 months. Babies with higher antibody levels at birth tended to need treatment for longer, which can help doctors give families an idea of what to expect. No serious side effects of methimazole were recorded.

Four of the 12 babies later developed a temporary under-active thyroid because the brain's control centre was slow to restart, and they needed thyroid hormone medicine for a while [3]. All four had an extremely low TSH level at birth, while none of the six babies with a less suppressed TSH developed this. This was a small group of babies who were already sick enough to need treatment, so "4 in 12" does not describe the chance for all babies of mothers with Graves' disease. The authors' advice is simply that babies with very low TSH at birth should have their thyroid checked again after the over-active phase has settled. You can read more about this kind of under-active thyroid in our article on congenital hypothyroidism beyond the heel-prick.

What this means for you and your baby

Most babies of mothers with Graves' disease are healthy. The tests are a safety net. Helpful questions to ask your care team include whether your antibody level has been checked in pregnancy, whether it has been recorded in your baby's plan, whether cord blood will be tested, and when your baby's thyroid blood tests are due. If you take antithyroid medicine, it is especially important that the test in your baby's second week happens, even if earlier results were normal. If your baby needs treatment, ask how long follow-up will continue afterwards.

What researchers are working on next

Researchers now need to work out safe antibody levels for each of the main laboratory tests in use, check whether simpler hospital plans are followed more reliably, and study larger groups of treated babies to learn how often the later under-active thyroid happens and whether it affects development. The Japanese team notes that their study did not look at children's long-term development, which is an important next step [3].

The bottom line

A mother's antibody test, read against the right numbers for the right laboratory test, can show which babies need closer watching. Hospitals need to make sure the planned checks after birth really happen, and babies who need treatment, especially those with very low TSH at birth, benefit from being watched a little longer.

References

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  2. Pathmanathan U, Wingate A, Teasdale S. Neonatal Surveillance Gaps in Maternal Graves' Disease: Findings From a Queensland Maternity Hospital. Aust N Z J Obstet Gynaecol. 2026;66(3):e70140. doi:10.1111/ajo.70140 ↩
  3. Adachi E, Iemura R, Tanaka Y, et al. Clinical features of neonatal Graves' disease revealed by twelve cases that require- antithyroid therapy. Clin Pediatr Endocrinol. 2026;35(1):57-66. doi:10.1297/cpe.2024-0085 ↩
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