Hormones and fluid balance during pregnancy, labor and post partum

Abstract: The aim of this thesis was to determine any association between plasma oxytocin and vasopressin concentrations and renal water and sodium excretion during normal pregnancy. In addition to investigate changes in concentrations of estradiol, progesterone, oxytocin, cortisol, and glucose in the blood before and in the nearest hours after delivery and if treatment with oxytocin affected these concentrations and the fluid balance during the different stages of labour.Oxytocin, vasopressin, estradiol, progesterone, and cortisol were analysed in blood plasma or serum by radioimmunoassay or ELISA: serum glucose, and osmolality, and sodium in plasma and urine were  analysed by standard laboratory techniques.Fifty-seven women were studied during pregnancy and fifty-one during parturition and post partum. The low plasma vasopressin and increasing plasma oxytocin concentrations with unchanged water and sodium excretion indicate that oxytocin assists vasopressin in concentrating urine during pregnancy.Plasma vasopressin concentration continued to be low during parturition and post partum. Urine flow and concentration was unrelated to changes in plasma sodium concentration, indicating regulation of fluid balance during parturition was different to the non-gravid state. Women with weak myometrial contractions during parturition (slow progress of labour) reacted differently than women with normal parturition and a group of women with fast progress of labour. The group with slow labour had lower serum estradiol concentration in the latency phase and became hyponatremic. Pulsatile and continuous oxytocin infusions were both effective in the treatment of slow progress of labour. A lower amount of oxytocin was needed to affect delivery when given as pulsatile infusion.Serum cortisol and glucose concentrations were high during labour and cortisol level remained elevated after delivery and glucose concentration reached the highest levels (12 mmol/L) at the same time. Insulin resistance together with the long time of elevated cortisol concentration partly explained the high glucose concentration. In conclusion, fluid balance is not regulated according to the usual sensitive osmotic and volumetric influence on vasopressin release from the neurohypophysis during pregnancy and parturition. Parturition involves a change from one demanding condition, pregnancy, to another, lactation. Parturition and the hours directly after delivery are a turbulent period involving considerable stress.