Most women enjoy best sex as they approach 40 because they fear that their "biological clock" is ticking, say researchers.

A new study has found women are more likely to have sexual fantasies and affairs in their 30s and early 40s than in their younger years, despite the fact their bodies may be in decline.

According to the researchers, this is because as women approach the milestone they may sense that their "window of opportunity" to have kids is closing and their fertility is declining, 'The Daily Telegraph' reported.

And, this instinctual reaction is an increased appetite for sex, said the researchers who have based their findings on a survey of 900 women.

The survey divided respondents into three groups – those at their most fertile (aged 19 to 26), those whose fertility was declining (aged 27 to 45) and those who were approaching or had reached the menopause.

When it comes sharing sexual fantasies, even the ''closest'' couples find it hard to communicate their innermost ''naughty acts'' to each other. But if you're one of those who don't want to miss out on the fun, then here are few tips to get your mind ''moving''.

Not many couples are able to act out their sexual fantasies even if they are pro in the sack. The problem-How to share your wild thoughts? What would your partner think about you? How would he/she react? Will they comply or not?

Such questions and many others flood the minds of many sexually active adults who want to explore their wildest of sexual dreams, reports Fox News.

While sharing lewd, obscene, or sensuous scenes with your partner can pose to be a big problem, it also has an upside- not only can you divulge your sexual desires but could even get a sneak peek into your lover's libidinous thoughts as well.

So if you want to spice things up by sharing it all, sex and relationship expert Dr. Yvonne Kristin Fulbright's guide will prove a saviour for you.

And she says that before taking the plunge and share, you should first ask yourself the following questions:

1. What's my motivation?

Why do you want to share this fantasy? What turns you on about sharing? Do you hope the sharing can be a form of foreplay or something more? Are you hoping that your fantasy will be fulfilled? Will it be advantageous to your relationship to share, revving up sex for the both of you?

2. Will sharing diffuse my own pleasuring?

Many lovers like to have a few tricks up their sleeves in bed, and their private fantasies are often what makes or breaks the sexual moment. Whether it's getting through a sex act or working your way to orgasm, will sharing take away from how your fantasy benefits you now? Will you be able to enjoy having the cat out of the bag?

3. Am I in the right kind of relationship for sharing?

Not every relationship can weather such intimate sharing. You need to be in a secure, trusting relationship. Your sexual union should be able to provide you with the support and safety needed to get over any nervousness and anxiety, and to field any reactions. Lovers need to make each other feel accepted and emotionally safe. This includes being able to refuse a request to act out a fantasy without putting the other down.

4. Can my partner handle my fantasies?

Some lovers can't handle hearing about certain sex acts, especially if they involve "who" you''re fantasizing about. Partners who are sex negative or uncomfortable with sexual intimacy in general are not going to be the best candidates for such sharing. So consider what your lover may be open to and which types of fantasies may cause more harm than good.

5. Am I ready to hear my partner's fantasies?

Lovers tend to expect reciprocity when sharing fantasies. It's usually not a one-way street, so you have to consider how you might react to your partner's fantasies. Can you go there? How can you provide the same safety you're hoping for?

After the self-questioning comes the sharing part, so think long and hard about when to open up. And don't expose a fantasy after a hot romp, for it may not be received as well as one meant to arouse desire.

Let your partner know that you want to share something and explain your reasons for wanting to share.

Finally, remind your lover that your relationship means more than any fantasy. Your partner should not feel undesirable at all.

A Hollywood hunk, ex-lovers, a blue film scene and even what to buy in a grocery store—these are things that women think of while having sex.

Some women have now revealed what really scores with them between the sheets.

Single comedian Shazia Mirza, 34, said that some of her friends revealed that during sex they are mentally writing a to-do list, remembering clothes they have to wash, what they've got to buy at Tesco's or those shoes they love in Selfridges.

And some women even think of men they secretly fantasise of.

"A friend of mine, who really loves her husband, told me that during sex she can't help thinking about all the men she secretly really desires, like Jeremy Beadle and Jeremy Paxman," the Sun quoted her as saying.

"I've been married twice and had many lovers and to be honest, with past lovers I've been so bored in bed, I've taken to compiling mental grocery lists and calculating exactly how many shoes are in the wardrobe (82 pairs)," said author Kathy Lette, 51.

"Most wives are taken for granted. But how we'd LIKE to be taken is by a muscular-thighed Adonis with pecs appeal.

"Luckily sex with Johnny Depp is only the flick of a light switch away. Ah, Johnny - a man whose sex appeal is so deadly it should be registered at police headquarters as a lethal weapon.

"Doing the horizontal tango with George Clooney is also amazing - if only he'd been with me at the time!" she added.

Sarah Millican, 33, is in a relationship, and she said: "I never walk out of a film at the cinema. I'm the same with sex. I always think it might get better. To be honest, as long as I've got a bag of Maltesers, I'm not going anywhere."