RCOG World Congress 2023

X-linked Hypophosphatemia in Pregnancy: Case Series with Management Outline

Dr M Christodoulou, Mr A Aref, Dr H Mahmoud

Introduction

Familial X-linked hypophosphataemia rickets1

Rare inherited condition of bone metabolism
Affects 1 in 20,000 individuals
Caused by a mutation in the PHEX gene resulting in
1. Excess production of FGF23 and thus (2)
2. Excessive urinary excretion of phosphate
50% risk of transmission to offspring

Bone Metabolism

Interactions between PTH, calcitonin and VitD as depicted in image 1
Role of FGF23 in calcium homeostasis was only recently discovered

➢ its function is to prevent VitD mediated hyperphosphatemia

➢ Net effect of FGF23 is to decrease phosphate2

Pregnancy

Is a period of increased calcium requirement to encourage growth of foetal tissues
Most of calcium and phosphate transport occurs in the third trimester against a concentration gradient2.

Aim:

Case series of two sisters with XLH followed up during pregnancy at Medway Hospital from October 2021 to December 2022 with an aim to highlight the management and outcome of this rare condition in pregnancy.

Design and Methodology

Timescale: October 2021 to December 2022
Methods: Electronic records of their pregnancies were reviewed, including antenatal clinics, emergency presentations and admissions as well as delivery outcomes.
Analysis: Excel was used for calculations. Results and management compared to PubMed literature using search words.

Results

Booking phosphate levels 0.34mmol/L and 0.4mmol/L Antenatal planning

Medication: Alfacacidol, PO Phosphate & Aspirin 150mg due to high risk of IUGR.

Serum phosphate levels measured every 3wks in first two trimesters and weekly during third trimester (trends shown in graph 1)

Additional fetal growth scans on weeks 28, 32 and 36wks 3rd trimester and intrapartum care

During 3rd trimester IV phosphate replacement was used.

Parenteral phosphate was also used intrapartum requiring MCU admission to monitor electrolytes.

Pre-delivery levels of phosphate were 0.52 mmol/L in both cases

Planned delivery method at 37wks by elective uncomplicated caesarean section due to the associated rickets bony pelvis affection (Rachitic Pelvic Osteo-dystrophy).

First delivered at 36 weeks+3 due to resistant hypophosphatemia with a baby weight 2920 g.

The second delivered at 37 weeks+2 with baby weight 2725 g.

Protocol for IV phosphate replacement

Admission to MECU and overnight stay
IV infusion of Monofer iron
Followed by an infusion pump of 30mmol of

phosphate infusion over 12hrs with a maximum infusion rate of 10 mmol/hr to avoid hypocalcaemia.
Four hourly VBGs were performed to monitor calcium levels.
Overnight stay and repeat bloods next morning with aim of phosphate > 0.3 mmol/L

In the case of resistant hypophosphataemia, the reinfusion included IV phosphate 50mmol over 12hrs using infusion pump at rate of 10 mmol/hr.

Conclusions

Two relatives with XLH-Rickets managed at Medway Maternal-Medicine-Centre with Endocrinology Input with good neonatal and maternal outcome.
Regular blood tests for serum phosphate levels and additional growth scans performed
Aim to keep IV phosphate use limited for third trimester to reduce risk of hypocalcaemia
Increased demand of phosphorus in 3rd trimester is in keeping with literature4
Delivery via ELCS
Limited previous literature demonstrated similar management5

Limitations

No control of confounding factors
Small number of participants / difficult to generalise results
Young age of participants
No guidelines for requirement of IV phosphate; thus, clinical judgement had to be

used.
Limited literature to compare

RCOG World Congress 2023

X-linked hypophosphatemia in pregnancy. Very rare Case series with management outline.

Poster Presenter

Authors

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