A 40-year-old woman was referred to Chiba University Hospital (Chiba, Japan) at 34 weeks gestation because of an abnormal mass observed in the neck of her fetus, which was noticed at the scheduled check-up at 34 weeks. The patient had been infertile for 3 years after two spontaneous abortions. Infertility workup revealed adenomyosis (47 ϫ 45 mm) of the uterus; the patient was otherwise normal. The patient's TSH level (0.66 IU/mL), measured at 8 weeks before conception, was within normal limits. She had undergone hysterosalpingography (HSG) with 10 mL of ethiodized oil (Lipiodol; Guerbet) on day 8 of a menstrual cycle, followed by artificial insemination using her husband's sperm, resulting in successful conception on the HSG treatment cycle. Ultrasonography demonstrated a 55 ϫ 36 ϫ 32-mm hypervascular mass at the anterior part of the neck of the fetus (Figure 1, A and B). Three-dimensional imaging revealed a large goiter, possibly preventing neck flexion ( Figure 1C). Persistent brow presentation indicated cesarean section, and the patient delivered a 2844-g baby boy at 37 weeks and 3 days of gestation, with an Apgar score of 8 at 1 minute after delivery. The baby's goiter resolved spontaneously and became impalpable at postnatal week 4. Abnormal thyroid function of the baby (TSH, free T 4 , and free T 3 were 88.1 U/mL [reference range, 4.5-14.5], 0.60 ng/dL [1.05-1.61 ng/dL], and 2.33 pg/mL [1.43-2.19 pg/ mL], respectively, in cord blood; and 190.6 U/mL [8.09 -38.9 U/mL], 0.66 ng/dL [1.37-3.65 ng/dL], and 2.77 pg/mL [1.59 -8.11 pg/ml], respectively, in peripheral blood obtained shortly after birth) resolved without treatment by postnatal day 7 (TSH, 8.45 U/mL [0.51-4.57 U/mL]; free T 4 , 1.35 ng/dL [0.96 -4.08 ng/dL]; and free T 3 , 3.57 pg/mL [2.65-4.57 pg/mL]). Iodine concentration in neonatal urine determined on postnatal day 7 was 980 g/L, which was higher than the upper limit (300 g/L) for preschool infancy and the lower limit (185 g/L) for an iodine-exposed newborn (1). Thyroid function tests of the neonate conducted thereafter have been normal, and no palpable goiter has recurred until 2 years of age. Maternal thyroid function (TSH, 1.2 U/mL; free T 4 , 0.92 ng/dL; and free T 3 , 2.56 pg/mL) was normal, and thyroid-related autoantibodies were not detectable at 34 weeks gestation. Figure 1. Fetal ultrasonography at 35 weeks gestation. A, Image of a transverse plane of the fetal neck. Enlarged thyroid gland (arrowheads) completely surrounds the trachea (asterisk). The arrow indicates the fetal esophagus. Images in the upper left and lower right corners are the anterior and posterior fetal images, respectively. The amniotic fluid index was 21 cm. B, Image of an oblique coronal plane of the fetal neck. Lobes of the thyroid gland are seen on both sides of the trachea (asterisk). The triangles indicate vertebral bodies in an extended attitude. Images in the upper right and lower left corners are the cranial and caudal fetal images, respectively. C, Three-dimensional imaging of the anterior part of the fetal nec...
