We report a case of fetal goitrous hypothyroidism followed by neonatal transient hyperthyroidism. A fetal goiter (26 × 38 mm) was detected by ultrasound and magnetic resonance imaging at 29 weeks of gestation. Hypothyroidism was confirmed by cordocentesis, which revealed an elevated TSH (255 µIU/ml) and a low free T4 (0.4 ng/dl). The fetal goiter decreased in size after treatment with four 240-microgram intra-amniotic administrations of levothyroxine. A 2,829-gram male neonate was delivered vaginally at 37 weeks of gestation, showing an euthyroid status at birth. On day 3, free T3 was 6.9 pg/ml and free T4 was 6.4 ng/dl, indicating hyperthyroidism. This persisted for 4 months. His thyroid functions reverted to normal at 4 months of age and have been within normal range since. Undetermined factors might be involved in the development of thyroid dysfunction in the perinatal period.

To determine safety and efficacy of exclusive human milk diet (EHMD) for very low birth weight (VLBW, <1500 g) infants. Prospective, controlled, open trial of VLBW infants randomized to EHMD (mother's own milk [MOM]/donor milk [DM] with human milk-based fortifiers) or Standard Diet (MOM/DM with cow milk-based fortifier/formula). Outcomes included superiority of weight gain velocity from birth to 34 weeks gestational age, time to full feeds, and safety. In total, 147 infants received EHMD (n = 77) or Standard Diet (n = 70). The EHMD group had superior mean weight gain velocity versus the Standard Diet (13.44 vs 11.96 g/kg/day, p = 0.006) and earlier mean time to full feeds (20.0 vs 25.9 days, p = 0.03); adverse events were not significantly different (32.5% vs 21.4%, p = 0.13). EHMD is viable for management of VLBW infants, providing improved growth without reduced safety. Japan Registry of Clinical Trials: jRCT2031210384.

Several cut-off points for 25-hydroxyvitamin D (25(OH)D) levels have been proposed to determine vitamin D deficiency or insufficiency. However, the level for 25(OH)D deficiency in early infancy remains unclear. The serum 25(OH)D value at which parathyroid hormone level plateaus, called the "inflection point," is considered the most appropriate criterion for defining an adequate vitamin D status. This was a single-center retrospective study involving 305 1-month-old and 252 2-month-old Japanese infants. Nonlinear segmented regression analysis was performed based on the correlation between 25(OH)D and parathyroid hormone levels to determine vitamin D deficiency cut-off points. Inflection points were 7.90 ng/mL for 1-month-old (95% confidence interval, 6.31-9.49) and 6.74 ng/mL for 2-month-old (95% confidence interval, 5.80-7.68) Japanese infants, which were lower than previously reported. Cut-off values were also lower in the high-body mass index (BMI) group than in the low-BMI group for both 1-month and 2-month-old infants. These results imply the need for nutritional rickets prevention via policy recommendations in most full-term newborns in Japan. Although validation studies are required, these results can still be used to guide vitamin D insufficiency treatment options in early infancy.

Vitamin D seasonality has been reported in adults and children, suggesting that sunlight exposure has effects on 25(OH)D production. While vitamin D deficiency among infants has received significant attention, little is known about the extent to which vitamin D status during early infancy is affected by sunlight exposure. Here, we retrospectively analysed serum 25(OH)D levels of 692 samples obtained from healthy infants aged 1–2 months born at Saitama City Hospital, Japan (latitude 35·9° North) between August 2017 and September 2021. Data regarding the frequency of outdoor activities, formula intake and BMI were also collected and analysed. Month-to-month comparisons of vitamin D levels revealed significant variation in 25(OH)D levels in breastfed infants starting at 2 months, with maximal and minimal levels in September and January, respectively. An outdoor activity score of 0 was most common at 1 month (83·9 %) and a score of 3 was most common at 2 months (81·2 %), suggesting an increased amount of sunlight exposure at 2 months. Multiple linear regression analysis revealed the amount of formula intake to be significantly associated with vitamin D status at both 1 (t = 17·96) and 2 months (t = 16·30). Our results comprise the first evidence that seasonal variation of vitamin D begins at 2 months among breastfed infants from East Asia, though dietary intake appears to be the major determinant of vitamin D status. These findings provide new insights into the influence of dietary and non-dietary factors on vitamin D status during early infancy.

Maternal use of magnesium sulfate has been associated with neonatal hypocalcemia and bone changes. We report the case of a preterm male infant who presented hypercalcemia before developing hypocalcemia after maternal magnesium sulfate therapy. Magnesium sulfate was used for premature rupture of membranes for 32 days, and the patient was delivered at 33 weeks gestation. The cord blood showed ionized calcium 1.54 mmol/L. His serum calcium and magnesium were 11.4 mg/dL and 3.5 mg/dL after birth and fell to 6.6 mg/dL and 2.7 mg/dL at 6 hours, respectively. The intact parathyroid hormone level was 18 pg/mL at 6 h. Radiography showed transverse radiolucent metaphyseal bands of the proximal humerus bone, suggesting disturbance in normal ossification. Transient hypercalcemia before the development of hypocalcemia after maternal magnesium sulfate therapy has not been previously reported. We speculate that maternal long-term magnesium sulfate therapy led to defective ossification and transient hypercalcemia in the offspring. Subsequent hypocalcemia was thought to be due to the inhibition of parathyroid hormone secretion by hypercalcemia and hypermagnesemia.

Screening-based intrapartum antibiotic prophylaxis (IAP) has reduced the prevalence of early-onset group B Streptococcus (GBS) infection in newborns. Nevertheless, early-onset disease still occurs despite IAP, and IAP is not effective in preventing late-onset disease. This study aimed to determine the prevalence and risk factors of GBS neonatal umbilical colonization managed by dry cord care in Japan. Of 735 healthy newborns in the well-baby nursery at Saitama City Hospital, 353 from whom umbilical bacterial swabs were obtained before discharge were included in the analysis. Maternal and neonatal clinical characteristics were retrospectively reviewed. GBS was detected in 4.2% (15/353) of umbilical swabs; 13/15 (86.8%) were born to GBS-negative mothers. The median (IQR) age at umbilical swab collection was 4.0 (4.0-5.0) days. Comparison of clinical characteristics between GBS-positive and negative neonates revealed a significant difference in the proportion of vaginal deliveries (15/15 [100%] in GBS-positive neonates vs. 115/338 [34.0%] in GBS-negative neonates, p < 0.0001). Of 15 GBS-positive neonates, 10 (66.7%) were also co-colonized with other enteric bacteria such as Escherichia coli. Vaginal delivery was a risk factor associated with GBS neonatal umbilical colonization in Japanese neonates. Co-colonization with multiple enteric bacterial species implicates vertical transmission of GBS from undetected carrier mothers during passage through the birth canal.