Endocrine Abstracts

A 37-year old woman developed grand-mal seizures shortly after having given vaginal birth at term. Three hours later, her newborn son also had a tonic-clonic seizure. Following the convulsions, maternal fractures of the humerus and the neck of femur were detected.

The pregnancy had been uneventful except for hip pains for 4 weeks prior to delivery. For years, the patient had been ingesting 5 l of bottled water daily. Labour had set in spontaneously and she received no intravenous fluids.

Maternal and neonatal serum sodium concentrations were 107 mM and 112 mM, respectively. Hypocortisolaemia was excluded and biochemical investigations implied raised vasopressin action in the mother. No abnormality was seen on MRI of the brain. Significant osteoporosis was noted on plain radiology.

At follow-up three months post partum, the patient revealed that during her teenage years she had had a dairy-free, erratic eating habit with weight loss and periods of secondary amenorrhoea. She continued to be physically active and her BMI was 19.4 kg/m², weighing 3 kg less than prior to pregnancy.

Multiple factors contributed to the hyponatraemia of mother and son. The threshold for vasopressin release is lower in pregnancy. Parturition and pain acutely stimulate vasopressin release. Oxytocin has antidiuretic properties due to the structural similarity to vasopressin. Lastly, on the day of delivery the patient had consumed an even larger than usual volume of hypotonic water.

The past history of a likely eating disorder can explain the tendency to ongoing compulsive water drinking and reduced bone mineralisation. The combination of an eating disorder, amenorrhoea and osteoporosis in active sportswomen is referred to as ‘Female Athlete Triad’.

Fetal water intoxication is a consequence of maternal hyponatraemia as osmotic conditions are passed on across the placenta. When assessing the mother for severe electrolyte imbalance, the newborn baby must be kept in mind.