SPERM MORPHOLOGY & FERTILITY

Sperm morphology

Refers to the shape, size, and appearance of sperm cells

Why is sperm morphology important

Abnormal sperm morphology decreases fertility and reduces the sperm's ability to fertilize an egg

What structures must normal sperm have to fertilize an egg

Proper structure to swim efficiently, reach the egg, penetrate the zona pellucida, and deliver normal genetic material

Effects of abnormal sperm morphology

Reduced fertility, difficulty fertilizing the egg, and possible need for assisted reproductive techniques

Four regions of a sperm cell

Head, neck, midpiece, and tail

Function of sperm head

Contains DNA and acrosome

Function of sperm neck

Connects the head and midpiece

Function of sperm midpiece

Contains mitochondria for energy production

Function of sperm tail

Propels the sperm forward

Characteristics of normal sperm

Oval head, intact acrosome, normal midpiece, single uncoiled tail, good forward motility, and normal genetic material

Kruger strict criteria

Criteria used to evaluate fertility potential based on sperm morphology

Normal morphology greater than 14%

Indicates high fertility potential

Normal morphology 4–14%

Indicates slightly decreased fertility

Normal morphology 0–3%

Indicates severely impaired fertility

Medical term for abnormal sperm morphology

Teratozoospermia or teratospermia

Causes of abnormal sperm morphology

Increased testicular temperature, toxic chemicals, infection, and genetic factors

Macrocephaly

A giant sperm head

Significance of macrocephaly

Associated with extra chromosomes, poor fertilization, and may be inherited

Macrocephaly genetic association

Aurora kinase C mutation

Microcephaly

A small sperm head

Problems associated with microcephaly

Defective acrosome and reduced genetic material

Pinhead sperm

A very tiny head containing little or no paternal DNA

Pinhead sperm association

Diabetes

Tapered head

A cigar-shaped sperm head

Tapered head associations

Varicocele, high scrotal temperature, abnormal chromatin, and aneuploidy

Thin head

An extreme form of tapered head

Possible causes of thin head

Broken DNA, varicocele, and defective head formation

Decondensing head

A defect in which DNA prematurely unravels inside the sperm head

Globozoospermia

Round-headed sperm with an absent or defective acrosome

Problem with globozoospermia

Cannot activate fertilization normally because of the absent or defective acrosome

Headless sperm

Also called acephalic sperm or decapitated sperm syndrome

Characteristics of headless sperm

Has no head, no DNA, and no chromosomes

Nuclear vacuoles

Large or multiple vacuoles within the sperm head

Significance of nuclear vacuoles

Still under investigation, with some studies showing reduced fertility and others showing no significant effect

Multi-head sperm

Sperm with two or multiple heads

Multi-head sperm associations

Toxic chemicals, heavy metals, smoking, and high prolactin

Thick swollen neck

A midpiece abnormality caused by defective mitochondria

Other causes indicated by a thick swollen neck

Broken or absent centrioles

Result of defective mitochondria in sperm

Poor energy production → poor motility

Other sperm midpiece defects

Distal midpiece reflex, abaxial attachment, accessory midpiece, thickened midpiece, kinks, gaps, and tail stump defect involving the midpiece

Dag defect

A coiled midpiece

Coiled tail

A tail abnormality associated with bacteria, improper seminal fluid conditions, and heavy smoking

Problem with a coiled tail

The sperm cannot swim properly

Stump tail

Also called dysplasia of fibrous sheath or DFS

Characteristics of stump tail

Short tail with poor or absent motility

Stump tail associations

Genetic disease, autosomal recessive inheritance, immotile cilia syndrome, and increased aneuploidy

Tail-less sperm

Also called acaudate sperm

Tail-less sperm is seen during

Necrosis

Other sperm tail defects

Bent tail, folded tail, broken tail, terminal tail coil, and coiled tail with accessory midpiece

Effect of abnormal sperm morphology on fertility

May cause reduced fertility, delayed conception, poor fertilization, and need for reproductive assistance

Assisted reproductive options for poor sperm morphology

IUI, IVF, and ICSI

IUI

Intrauterine insemination

IVF

In vitro fertilization

ICSI

Intracytoplasmic sperm injection

Why does ICSI have the highest success among the listed assisted reproductive options

A selected sperm is injected directly into the egg

Can sperm shape improve

Yes, through lifestyle improvements

Lifestyle changes that may improve sperm morphology

Exercise, avoiding testosterone abuse, stopping smoking, avoiding alcohol and drugs, reducing caffeine, losing excess weight, avoiding hot tubs, reducing stress, wearing loose cotton underwear, and consuming antioxidants

How long does it take for a new sperm population to develop

Approximately 3 months

Why do lifestyle improvements take about 3 months to affect semen quality

A new sperm population takes approximately 3 months to develop

Minimum number of sperm cells to evaluate for morphology

At least 100 sperm cells

Recommended microscopy magnification for sperm morphology

1000× microscopy whenever possible

Common stains for sperm morphology assessment

Eosin-Nigrosin, William's stain, Modified Giemsa, Diff-Quik, and Papanicolaou stain

Gold standard microscopy for many sperm abnormalities

Differential Interference Contrast or DIC microscopy of fixed, unstained samples

DIC microscopy is especially useful for

Detecting acrosomal and subtle head or midpiece defects

Electron microscope advantage in sperm assessment

Provides the most detailed visualization

Electron microscope limitations

Expensive, complex, and difficult to quantify

Computer-Assisted Sperm Analysis, CASA

An automated sperm analysis system

Advantages of CASA

Fast, automated, and easily quantified

Why is acrosome assessment important

A functional acrosome is necessary for fertilization

Specific stains for acrosome assessment

Modified Giemsa, Wells-Awa, and Casarret's

Fluorochromes used for acrosome assessment

Lectins, FITC-PSA, and CTC

What do acrosome stains and fluorochromes assess

The presence or integrity of the acrosome

Macrocephaly major problem

Giant head

Microcephaly major problem

Small head

Pinhead major problem

Little DNA

Tapered head major problem

Associated with varicocele

Thin head major problem

DNA damage

Globozoospermia major problem

No acrosome

Decondensing head major problem

DNA unraveling

Headless sperm major problem

No chromosomes

Thick swollen neck major problem

Defective mitochondria

Coiled tail major problem

Poor motility

Stump tail major problem

Genetic defect and immotility

Tail-less sperm major problem

Associated with necrosis

Multi-head sperm major problem

Associated with toxic exposure

Abnormal sperm morphology medical term

Teratozoospermia

Sperm morphology associated with no acrosome

Globozoospermia

Sperm abnormality associated with diabetes

Pinhead sperm

Sperm defect associated with varicocele

Tapered head

Sperm abnormality lacking chromosomes

Headless sperm

Sperm abnormality caused by defective mitochondria

Thick swollen neck