Thyroid volume, urinary and milk iodine in mothers after delivery and their newborns in iodine-replete country.

OBJECTIVE

To estimate thyroid volume (ThV) in primiparous (PP) and multiparous (MP) mothers (MO) and their newborns (NB) as related to their urinary iodine and thus contribute to the question on the interrelation between iodine intake during the pregnancy and thyroid function in pregnant women.

METHODS

The ThV by ultrasound was estimated in a total of 258 MO (108 PP and 150 MP)) and their newborns on the 4th-7th day after delivery. There were 227 in term and 31 preterm (before 37th week) deliveries. In addition, ThV was estimated in double amount of controls (216 vs. PP and 300 vs. MP) in the same age range and nearly age matched which were either nulliparous or did not have delivery within last 12 months. Urinary iodine concentration was estimated in spot urine samples obtained from 75 MO and their NB and milk iodine in 44 milk samples obtained between the 4th and 7th day after delivery.

RESULTS

On the first week after delivery, the ThV in all 258 MO was significantly higher than that in 516 of nearly age matched females (mean+S.D.: 14.87+4. 93 ml vs. 10.61+4.02 ml, resp., P<0.01). Although the ThV was lower in 108 PP than in 150 MP women (mean+S.D.: 13.85+4.51 ml vs. 15.59+5. 11 ml, resp., P<0.01), it was still significantly higher (P<0.01) than that in a double amount of nearly age matched controls for PP (9.96+3.15 ml) and MP (11.07+4.48 ml). Mean ThV found in all 258 NB was 0.60+0.21 ml (median 0.5 ml, range 0.2-1.6 ml), the values in those born in term being higher than in preterms (mean+S.D. 0.62+0. 20 ml vs. 0.45+0.12 ml; P<0.01). No correlation was found between the ThV and body weight in NB. However, significant correlation was found between the ThV in all 257 NO and their NB (r=0.292, P<0.05). The mean value of urinary iodine in mothers on the first week after delivery was 9.0+7.2 ug/dl (median 6.1, range 3.0-47.2). The average urinary iodine in primiparous was slightly higher than that in multiparous mothers (10.3 vs. 8.4 ug/dl; not significant). In newborns, the mean urinary iodine in the first week after birth was 11.6+7.6 ug/dl (median 6.5, range 0.745.0).

CONCLUSIONS

The finding of about 30 % higher ThV in 258 mothers after delivery than that in double amount of nearly age matched women (P<0.01) who were either nulliparous or did not have delivery at least within last 12 months shows that, in spite of general satisfactory iodine intake in Slovak population, the iodine intake during pregnancy was not satisfactory. This is supported by the data on urinary iodine which was higher in primiparous than in multiparous women.