VARIATIONS IN PLASMA THYROXINE DURING LABOUR AND EARLY PUERPERIUM

Abstract

ABSTRACT Repeated determinations of plasma T4, PBI, dialysable T4 and free T4 were undertaken on 31 mothers of full-term infants and ten mothers of premature infants in the perinatal period. The blood samples were obtained 2–7 hours before delivery, at delivery, 3–6 hours after delivery, 6–12 hours after delivery and on the 2nd, 3rd–4th and 5th–6th day after birth. Similar investigations were also undertaken on cord blood. A significant increase in the mean value for plasma T4 of approximately 25 % was found from before delivery to the time of delivery. This was followed by a rapid decrease, so that a return to values observed before delivery occurred on the 2nd day after delivery. Dial. T4 did not alter during the rapid variations in the plasma T4. Plasma T4 was found to be significantly increased in maternal blood at delivery as compared with cord blood but there was no significant difference in the mean values for free T4 in the cord blood and the maternal blood at delivery, suggesting a free passive passage of T4 via the placenta. The variations found have not been described previously and they provide a possible explanation for the disagreements between the results of previous investigators. The reason for the variations and their significance in assessing possible equilibrium between free T4 in the maternal blood and cord blood are discussed.