You've been trying to fall pregnant but haven't. Here are some possible reasons.

There are few things more anxiety-inducing than trying for a baby and not being able to fall pregnant. Suddenly, you find yourself wondering how long should it take to fall pregnant, what you could be doing differently, and if starting a family is in your future.

However, fertility experts recommend you don’t panic. There could be several reasons you can’t get pregnant right now, and not all of them will require intervention.

Still, it’s best to be informed and learn some possible causes as well as find out when you should seek medical assistance.

Here, gynaecologist and fertility specialist Dr Georgiana Tang of City Fertility Centre shares the most common reasons a couple can’t get pregnant despite trying.

1. Your age.

We all know egg quality, and therefore fertility, decreases in women after a certain age — about 37. Dr Tang says because of this, your age also plays a “very important” factor when you might want to consider getting help.

Aged under 37? It could still take several months to fall pregnant naturally, even if you and your partner are both perfectly healthy. If you’ve been trying for nine to 12 months, Dr Tang advises you to have a chat to your doctor.

If you're between 37 and 40 and have been trying for six to nine months, it might be time to seek professional advice.

Dr Tang says those women older than 40 who really want to have children should seriously consider getting help after six months of trying. That's because the rates of successful IVF are almost zero after 44.

2. Whether you're ovulating.

This one's an obvious reason for infertility, but what you might not know is that you can get your period regularly and still not be ovulating - even when you're not taking any form of birth control.

Dr Tang says "even people who have monthly bleeds, may not be ovulatory", so people should watch for other signs, such as changes in discharge or by using an over-the-counter ovulation test.

3. Lifestyle factors.

According to Dr Tang, the following lifestyle factors can negatively affect fertility in both men and women:

• Smoking;
• Being overweight;
• Eating an unhealthy diet;
• Being stressed.

4. When you're having sex.

Dr Tang says having sex too infrequently - or even too often - can affect your chances of getting pregnant. She says people might wrongly assume the more sex the better when it comes to trying for a baby, but she warns doing it too often, say every morning and night, can reduce the sperm count.

Similarly, if you have sex too few times, you might miss your ovulation that month.

"The sperm lasts for about three days in the system, so you don't need to do it daily. Every second or third day is adequate," Dr Tang says.

For your best chances of getting pregnant, calculate the 14th day of your cycle and have sex every two to three days that week. So if you ovulate on a Wednesday - have sex on the Sunday or Monday, again on the Tuesday or Wednesday and then also on Friday.

Listen: Mia Freedman chatted to her cousin Sylvia who has endometriosis.

5. Medical conditions.

If you have been diagnosed with polycystic ovarian syndrome or endometriosis you already know these conditions can affect your fertility. But you could also have these conditions without knowing it.

Dr Tang advises going see your doctor if you experience heavy, painful periods - as this could be a sign of endometriosis. PCOS symptoms include irregular periods, excess hair growth and acne.

6. Blocked fallopian tubes, cysts or fibroids.

Dr Tang explains these three complications in a woman's reproductive organs can each be preventing you from falling pregnant.

"People can have an infection without knowing and the fallopian tubes can be blocked," Dr Tang says.

Meanwhile, fibroids are benign growths found in the uterus, which could have no symptoms or result in heavy periods. Sufferers of ovarian cysts may feel pain on one side of their lower abdomen.

7. Male fertility issues.

With much of the infertility conversation focussed on women, it can be easy to forget the male partner could be the reason a couple can't get pregnant.

Dr Tang says if men have abnormal sperm readings - either there are too few of them or they're not swimming properly - they will likely have no symptoms.

She says men's sperm production and quality can be affected by lifestyle factors such as stress, a poor diet, smoking and a lack of exercise.

Finally, men's age does play a role in fertility, but it's not as strongly pronounced as the role it plays in women's fertility and there is no sharp decline in fertility after a certain age.

If you've been trying for a few months and are concerned about your fertility, Dr Tang recommends you seek medical advice, but also assures that getting pregnant can just sometimes take time, explaining only one in five young couples will get pregnant after one month, while about 90 percent of these couples will achieve pregnancy after a year of trying.

"You don't want to be super anxious and start to wonder if you've got fertility problems after trying for a month."

Dr Georgiana Tang is a gynaecologist and fertility specialist. She practices at City Fertility Centre.