Red deer foetal ageing manual

Red deer foetal ageing manual

by Ian Scott and Geoff Asher, AgResearch

Technical notes on images in the manual 

This manual is a pictorial presentation of actual images of known-age red deer foetuses from 20 to 80 days of age. The images were obtained using a BCF Easi-Scan real time scanner fitted with a 5 MHz linear array rectal transducer. Mode selection was set at ‘Ovary/Early Pregnancy’ and the grid display was set at 1 cm.

Identical images are presented adjacently with and without annotation.

An attempt has been made to collate ‘typical’ freeze images for each age group. However, real time ultrasound imaging is ‘dynamic’, with the 2-dimensional plane of the ultrasound transducer slicing quickly through the conceptus to create a mind’s-eye view of the 3-D structures. The ‘art’ of foetal ageing lies in a rapid determination of this 3-D image through which its size, shape, and other morphological landmarks can together be treated to indicate age. This is further complicated by the particular orientation of the foetus as it is being scanned:is it in cross-section, longitudinal section or oblique section (see below for definitions).

Competency in foetal ageing improves with practice as one starts to develop the mental picture of the 3-D image from what can be seen on the screen. An experienced operator can make an accurate judgement of foetal age within 10 seconds of locating the foetus or other diagnostic structures. This manual, therefore, is designed to help operators calibrate their assessments.

Orientation of the image

The term ‘longitudinal’ refers to an image that is obtained by slicing the foetus from cranial (head) to caudal (tail) and may be:

  1. Sagittal – a longitudinal plane that slices the foetus from ventral to dorsal (belly to spine) dividing the body into right and left halves.
  2. Dorso-ventral – a longitudinal plane that slices the foetus from side to side (laterally) dividing the body into lower (ventral) and upper (dorsal) halves.
  3. Oblique – a longitudinal plane that slices through the foetus at an angle.    

The term ‘cross-section’ refers to an image that divides the body into cranial and caudal (head and tail) portions (i.e. it is perpendicular to the longitudinal plane). A cross-section may also be at an oblique angle.

 



[1] Since within the first 70-80 days of gestation there is little effect of foetal genotype on the rate of foetal development, no adjustments are required for wapiti-type animals.