WHO Classification of Sperm Morphology

The World Health Organization (WHO) has published criteria for evaluating sperm morphology and identifying abnormal forms.

Parameters:

(1) head shape

(2) head size

(3) acrosome size

(4) head – others

(5) neck and midpiece

(6) tail

Parameter	Normal Features
shape	oval with smooth margin
length	4 – 5 microns
width	2.5 – 3.5 microns
ratio of length to width	1.5 – 1.75
acrosome (distal clear zone)	40- 70% of head
cytoplasmic droplets	small (see below)
width neck and midpoint	neck just under 1 micron, straight
neck insertion	one of the long axial tips of the head
tail	straight, about 45 microns in length

Number of heads:

(1) double

Head shape:

(1) round

(2) tapered

(3) amorphous

(4) piriform (pear shaped)

Head size:

(1) small

(2) large

Acrosome:

(1) absent

(2) < 40%

(3) > 70%

(4) irregular

(5) vacuolated

Neck and midpoint:

(1) thin

(2) thick

(3) irregular debris

(4) large cytoplasmic droplets (the WHO manual says normal is < 50% of head diameter but says abnormal is > 33% in Figure 2.8, page 20)

(5) eccentric insertion into head

(6) bent

(7) short

Tail:

(1) double

(2) coiled

(3) bent

(4) short

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