There are many factors that may influence fertility in women, from her age to the presence of certain medical conditions.
For men, the quality and quantity of their sperm is also important.
Now new research, published in the Journal of Sleep Research in October this year, has found that how long a man sleeps may affect his sperm.
The study analysed sperm samples from almost 800 men.
It looked at men who either slept too little (6.5 hours or less a night), too much (more than nine hours) or for the 'right' amount of time - around seven to 7.5 hours a night.
They found that men who didn't sleep enough had 30 per cent lower integrity of DNA in their sperm compared to those who slept 7-7.5 hours a night.
Men who slept for more than nine hours reduced the stability of their sperm's DNA even further - by 40 per cent.
The co-author of this study, Dr Jia Cao, said this research tied in with previous findings, which found that sleeping too little or too much decreased both semen volume and total sperm count.
Sleep patterns can affect DNA integrity of sperm due to a number of different mechanisms, says Melbourne-based Obstetrician, Gynaecologist and IVF Specialist Dr Alex Polyakov.
One mechanism relates to a hormone that regulates sleep, called melatonin.
He explains that melatonin is a strong antioxidant that protects sperm DNA from oxidative damage.
So, if men either sleep too little or too much, it's possible they have low melatonin levels, which can result in more sperm DNA damage.
But do men really need to pay close attention to how much they sleep if they're trying for a baby?
While this study found an association between sleep duration and sperm, Dr Polyakov says it didn't prove that one thing caused the other.
He says the reason why men sleep for different lengths of time may also be more important than the actual number of hours they snoozed.
If you have a chronic mental or physical illness, for example, that can affect how much you sleep. But the effect on sperm may relate more to that illness, rather than how much you slept.
Therefore, Dr Polyakov says: "My advice would be to pay attention to sleep pattern only so far as to detect and treat other conditions".
If you're hoping to have a baby, he notes there are lots of ways men can improve sperm quantity and quality.
These include cutting back on drinking, quitting smoking and steering clear of illicit drugs (especially anabolic steroids and testosterone derivatives).
He says men should also exercise regularly, stick to a healthy weight and avoid exposure to environmental pollutants when possible.
They should also avoid exposing their scrotum to high temperatures – so, no long soaks in hot baths, or using a steam room and the like – as these can impact sperm.
If a man has an underlying medical condition that can affect sperm, he should also speak to his doctor about management.
Ejaculating regularly may also help.
Dr Polyakov says that's because sperm that hasn't been ejaculated is subject to oxidative stress, which decreases its quality. Their energy reserves also get depleted, which means they have lower motility (they move less).
"So the best result is usually achieved after 2-5 days of abstinence."
A men's supplement containing zinc (such as Menevit) may also be of some benefit as it may improve sperm quality, says Dr Polyakov.
The bottom line is, there are lots of known measures men can take to improve the quantity and quality of their sperm.
But if a man is otherwise healthy and simply likes an occasional sleep-in, or to stay up extra late, Dr Polyakov reassures there's no need to worry about its effect on your chances of having a baby.