J Clin Res Pediatr En docrinol 2012;4(2):111-113
DO I: 10.4274/jcrpe.553
Selim Kurtoğlu1,2, Mustafa Ali Akın1, Ghaniya Daar3, Leyla Akın2, Şeyma Memur1, Levent Korkmaz1,
Osman Baştuğ1, Selcan Yılmaz1
1Erciyes University Faculty of Medicine, Department of Pediatrics, Division of Neonatology, Kayseri, Turkey
2Erciyes University Faculty of Medicine, Department of Pediatric Endocrinology, Kayseri, Turkey
3Nevşehir Government Hospital, Department of Pediatrics, Nevşehir, Turkey
Ad dress for Cor res pon den ce
Şeyma Memur MD, Erciyes University Faculty of Medicine, Department of Pediatrics, Division of Neonatology, Kayseri, Turkey
Phone: +90 352 437 49 37 E-mail: email@example.com
©Jo ur nal of Cli ni cal Re se arch in Pe di at ric En doc ri no logy, Pub lis hed by Ga le nos Pub lis hing.
Congenital Hypothyroidism Due To Maternal
Radioactive Iodine Exposure During Pregnancy
In tro duc ti on
Radioiodine (I131) is a convenient, inexpensive, safe and
effective treatment for hyperthyroidism and thyroid malignancy in
children and adults (1,2). The use of I131 is absolutely
contraindicated during pregnancy principally because of the risk of
damaging the fetal thyroid gland and thus leading to
hypothyroidism or cretinism
hyperthyrotropinemia is observed
dose is below 10 mCi (7). Also, hypothyroidism and
hypoparathyroidism can concomitantly occur as a result of
maternal radioactive iodine (RAI) treatment (8). Here, we report a
young female patient who delivered a hypothyroid baby after she
was given RAI treatment accidentally, being unaware that she was
at the 12th week of her pregnancy at the time of therapy.
During the screening programme for congenital
hypothyroidism, a fifteen-day old male infant was found twice to
have a thyrotropin (TSH) level exceeding 600 mU/L. The patient
was referred to the neonatology unit of Erciyes University Faculty
of Medicine. Medical history revealed that the mother had
received methimazole therapy for 3 weeks due to multiple
hyperactive nodules and that this was followed by RAI treatment
(20 mCi). Subsequent to this treatment, the mother was detected
to be at the 12thweek of her pregnancy. It was reported that the
Radioactive iodine (RAI) is used effectively in the treatment of
hyperthyroidism and thyroid cancer, but it is contraindicated during
pregnancy. RAI treatment during pregnancy can lead to fetal
hypothyroidism, mental retardation and increased malignancy risk in the
infant. Pregnancy tests must be performed before treatment in all
women of reproductive age. However, at times, RAI is being used before
ruling out pregnancy.
We herein present a male newborn infant with congenital hypothyroidism
whose mother was given a three-week course of methimazole therapy for
her multiple hyperactive nodules and subsequently received 20 mCi RAI
during the 12thweek of her pregnancy. The patient was referred to our
neonatology unit at age two weeks when his thyrotropin (TSH) level was
reported to be high in the neonatal screening test. Physical examination
was normal. Laboratory investigations revealed hypothyroidism (free
triiodothyronine 1.55 pg/mL, free thyroxine 2.9 pg/mL, TSH 452 mU/L,
thyroglobulin 20.1 ng/mL). The thyroid gland could not be visualized by
ultrasonography. L-thyroxine treatment was initiated.
Key words:Key words: Pregnancy, hyperthyroidism, radioactive iodine, fetal
Conflict of interest:Conflict of interest: None declared
Re cei ved:Re cei ved:05.12.2011 Ac cep ted:Ac cep ted:26.01.2012
Kurtoğlu S et al.
Hypothyroidism due to Maternal Radioactive Iodine
mother remained euthyroid after the treatment and this was given
as the reason why fetal thyroid functions were not measured. The
baby was born spontaneously via the vaginal route at the end of
a 42-week pregnancy. At birth, body weight was 3840 g, length
was 52 cm and head circumference was 36.5 cm. On the 15th
postnatal day, the infant was 55 cm in length, weight was 4720
g, and head circumference was 37 cm. His anterior fontanelle
dimensions were 4x6 cm and those for the posterior fontanelle
were 0.5x0.5 cm. Otherwise, physical examination was normal.
The umbilical cord was still undetached.
A plain knee X-ray showed findings consistent with a
37-week gestation. Thyroid volume was measured as 0.1 mL
(normal= 0.8) by ultrasonography. Free triiodothyronine was 1.55
pg/mL (normal= 2.99-6.66), free thyroxine 2.9 pg/mL (normal=
6.6-23.7), thyrotropin (TSH) 452 mU/L (normal= 0.70-18.10),
thyroglobulin level 20.1 ng/mL (normal= 91), urine iodine level
was 3 μg/dL (normal= 10-20 μg/dL). TSH receptor antibody level
of the maternal serum was 2.4 U/L (normal= 0-10 U/L). The baby
was started on L-thyroxine therapy at a dose of 15 μg/kg and is
now being followed by our team.
Thyrotoxicosis in pregnancy can be treated using antithyroid
drugs as the first choice. Rarely, thyroidectomy can also be an
option, but RAI is contraindicated (9). RAI is not used in known
pregnancies, but its use in undetected pregnancies is rarely
reported (1,6). RAI given to a pregnant woman crosses the
placenta rapidly and reaches the fetus (10). After the 12th week of
gestation, the fetal thyroid gland starts uptaking and storing
iodine (11). Fetal serum RAI level reaches 75% of mother’s serum
level and RAI can persist in the fetal thyroid gland for
approximately 70-75 days (11,12). All fetal tissues, and especially
the thyroid tissue, are 2-3 times more sensitive to radioactivity as
compared to adult tissues (13). RAI concentrated in the thyroid
gland causes ablation (11,13,14). As was also the case in our
patient, RAI uptake increases and causes more severe injury in
iodine-deficient fetuses (15). Therefore, probably due to its total
destruction by RAI, the thyroid gland could not be detected by
ultrasonography in our patient.
RAI can create a lethal effect on the embryo and can
negatively affect brain development both directly by its
radioactive effect and indirectly by creating hypothyroidism
(13,14). Besides hypothyroidism, a fetus exposed to RAI can
have mental retardation, malformations, as well as an increased
cancer risk in the later years of its life (16). In some reported
cases, hypoechoic thyroid nodules were detected and resolved
with thyroxine therapy (17).
To prevent RAI exposure during pregnancy, it is crucial to
perform a proper pregnancy test in hyperthyroid female patients
and not just rely on medical history. For this purpose, the
American College of Radiology has prepared a guideline listing 4
different clinical situations that eliminate the possibility of
pregnancy (18). These are: 1- A negative result in a pregnancy
test performed within the past 72 hours, 2- A history of
hysterectomy, 3- A state of menopause for at least two years, 4-
A premenarcheal child aged 10 years or younger. Also, one
should keep in mind that pregnancy tests relying on urine or
serum hCG levels are not totally reliable in the first 8-10
postconceptional days, since implantation may not yet have
been completed during this period (19).
In conclusion, for women in reproductive ages who require
RAI treatment, the importance of performing a pregnancy test 3
days prior to the treatment needs to be emphasized. If a woman
who has received RAI therapy is later detected to be pregnant,
fetal thyroid function tests should be undertaken and prenatal
treatment should be initiated (6).
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Kurtoğlu S et al.
Hypothyroidism due to Maternal Radioactive Iodine