The birth of a first child is momentous. Not only is there the joy of a new arrival, but also the reassurance that you can count good reproductive health amongst your blessings.

Fast forward a year or two and you assume that conceiving number two will require no more than a few early nights -- but that might not be the case.

Unfortunately, the belief that once you are fertile you will always be fertile is a delusion, and many couples can experience difficulties conceiving second time around.

In fact secondary infertility -- the inability to conceive a second or subsequent child -- is on the increase. Despite this, secondary infertility is a little-known and often misunderstood condition.

"People with secondary infertility are often just bemused to find themselves in a fertility clinic," says Dr David Walsh of the Sims Fertility Clinic.

"They assume that things will happen eventually because they already have a child, and can be slow to get treatment for secondary infertility. But secondary infertility, like all infertility, is increasing.

"Around 30pc of our clients are in fact suffering from secondary infertility."

Deirdre Mackesy runs the Cork Natural Fertility Clinic. She says misinformation can make couples with secondary infertility more reluctant to seek treatment than people with primary infertility.

"It is not uncommon for a couple to be told to just keep trying, that it will eventually happen.

"While this may be true in some cases, in many others, advice like this only adds to the frustration and heartache experienced by a couple having fertility problems."

Difficulties

Like many others, Joanna Donnelly assumed that time and patience would sort out the difficulties she was having conceiving her second child.

After a normal and natural first pregnancy at 32, Joanna had no reason to suspect things would not go smoothly the second time around.

"To begin with things were just taking a lot longer the second time. I did conceive after nine months, but then the pregnancy ended in miscarriage. I was trying to be positive, to tell myself that miscarriages happen and that we should just keep trying.

"It didn't dawn on me that I could be infertile. But more and more months went by without success and we decided to check things out."

Joanna sought help and started on a frustrating road of ambiguous test results and failed treatments.

"Age and general health were on our side, we had already had a child, yet no-one could tell us what was wrong. Every time we had an investigation and the results were good I thought 'oh no!' I felt that if they couldn't find the problem then they couldn't solve the problem and it was very frustrating."

Despite six miscarriages and several rounds of fertility drugs and IUI (intrauterine insemination) the cause of Joanna's secondary infertility was never identified. Eventually, three years after beginning her quest, Joanna's IVF (In Vitro Fertilisation) treatment was successful and her second child, Tobias, was born 11 months ago.

While Joanna suffered from unexplained secondary infertility the majority of couples, once investigations have been completed, get some indication of the cause of the problem.

Because a couple has already had one child naturally, some of the causes of primary infertility, like fibroids, endometriosis or PCOS, are less likely to be a factor in secondary infertility; in fact many such conditions improve after a first pregnancy.

"The existing child represents the fact that the system has worked," says Dr David Walsh. "So the most important thing to assess when it comes to secondary infertility is whether the delivery of that first child caused some damage that has led to the subsequent infertility.

"It is not uncommon for a woman's tubes to be damaged after delivery, or for a woman to get a post-natal infection that can cause future problems. So those are the first things that need to be tested for."

Often there aren't any symptoms of damage or infection after birth. A post-natal infection might only provoke a very low-grade temperature, or no temperature at all. If post-natal damage or infection is ruled out, doctors will usually investigate the man's sperm quality next.

"Sperm quality can change over time," says Dr Walsh. "The man may have had variable sperm to begin with and it could have deteriorated further in the years since conceiving the first child.

Next, factors related to the woman's age can be a factor to consider in secondary infertility. If she was in her early 30s the first time and is now in her late 30s, then that can make a difference.

"Over time both the eggs and sperm could have deteriorated so there may be a problem that wasn't there before."

Deirdre Mackesy of the Cork Natural Fertility Clinic says a couple's general health can also be a factor and advises them to consider how their lives have changed since they conceived their first child.

Stress

"Lifestyles and diet can have a huge effect on fertility. The disturbed sleep and stress that comes with having one child can certainly feed into couples having problems the next time around.

"Since you were last pregnant you or your partner may have had an infection, gained weight, or started eating fewer healthy foods. These seemingly small variances in your life can have large repercussions on your reproductive health. It's important to build up the body again before becoming pregnant.

"We say people need to get healthy in these ways first, and then look at the other medical problems that need to be treated."

Treatment for secondary infertility varies depending on the cause of the problem.

Fertility drugs, IUI and IVF can all offer positive results. Alongside these medical procedures, there are several alternative therapies on offer from acupuncture and homeopathy to Chinese herbal medicine.

While the medical process of treating secondary infertility can be arduous, couples suffering from the condition warn that the emotional turmoil it brings can be equally disruptive.

Fiona McPhillips felt so isolated while

being treated for secondary infertility that she started a blog detailing her experiences.

Since the birth of her first son in 2003 Fiona went through three rounds of Clomid, three IUIs, two IVFs and suffered several miscarriages.

Tough

"Most people don't even know that secondary infertility exists. People make jokes about the fact that you only have one -- that now you know how tough it is you don't want more.

"Because you already have a child, people with secondary infertility can be pushed out from the infertile community as well, and there aren't as many places secondary infertiles can go for support.

"Yet there are a lot of things more difficult about secondary infertility. The fact that you have a child means that you can't just collapse in a heap after every failed month.

"There's a terrible guilt when you feel you're not being there for them as much as you should be because of what you're going through, that you're not enjoying their early years the way you should be. And there's a guilt about the fact that you can't give them a sibling, especially if they are asking for one."

Regardless of whether a couple already has a child, the monthly grind of fertility treatment is harrowing and lack of understanding for what is a painful medical condition can make things even worse.

Earlier this year Fiona published Trying To Conceive, a medical and personal guide for Irish couples seeking fertility treatment.

"One of the hardest things is dealing with other people and the ridiculous and insensitive things they say, like 'can you not just be happy with what you have,' or 'sure worse things could happen.'

"But if all you want is to have a family, then for you maybe there is nothing worse that could happen.

"Studies show that infertility patients have stress levels equalled only by cancer and AIDS patients, so my advice to anyone else going through secondary infertility would be to seek support and find others in the same boat.

"Whether it's face to face or online, having a good rant with someone in the same situation is really comforting."