Validation of a point-of-care serum progesterone cut-off for caesarean section timing in the bitch and its effect on neonatal outcomes

Abstract

The aim of this study was to evaluate, in a clinical setting, the use of a serum progesterone concentration (PC) cut-off value of 4.6 nmol/L, measured on a point-of-care assay, as an indicator for performing safe preparturient caesarean section (CS) in the bitch. Privately-owned bitches, carrying at least two foetuses, were admitted for prepartum management. A parturient CS was performed once cervical dilatation was observed on vaginoscopy, with vaginoscopies performed at 08h00, 12h00 and 17h00 each day. A preparturient CS was performed when PC was ≤4.6 nmol/L, with PC measured in bitches with a closed cervix at the 17h00 examination. A total of 293 preparturient and 92 parturient CS were performed, with 2102 and 723 puppies delivered, respectively. There was no difference between preparturient and parturient CS in terms of the proportion of stillbirths (p = 0.91) or puppies surviving to 2 h post-delivery (p=1.00). Among live puppies delivered via preparturient CS, 99.5% (1986/1996) had normal viability (Apgar score ≥7 out of 10), compared to 98.0% (680/694) in the parturient CS group (p<0.001). The use of vaginoscopy in prepartum bitches is essential to avoid delaying surgical intervention in those bitches that enter Stage I of labour prior to PC dropping to ≤4.6 nmol/L. A PC of ≤6.4 nmol/l (2 ng/ml) is traditionally considered to indicate the expectance of onset of parturition within the next day (24 h), and is widely used as a cut-off for planned CS, however practitioners should be aware of rare instances of PC hovering between 6.4 nmol/L and 5.0 nmol/l up to 100 h before the onset of spontaneous parturition when using a point-of-care assay. Further research to establish safe cut-off values for CS using other progesterone assay systems, and in a wider variety of breeds, is warranted.

HIGHLIGHTS • Preparturient caesarean section in the bitch can be performed safely. • With IDEXX Catalyst, serum progesterone concentration (PC) should be ≤ 4.6 nmol/L. • Vaginoscopy needed to identify bitches that enter Stage I of labour before PC drops. • A cut-off of 4.6 nmol/L may not be appropriate for other progesterone assays.