Put 50 couples in a room and chances are that seven or eight of them have a fertility problem. That is assuming they all want to start a family. In a society which reveres the family, however, childless couples have it tough.

"For many couples, having a baby is often an easy, uncomplicated and joyous time. But the effects can be devastating for those experiencing infertility," said Dr Suresh Nair.

The obstetrician, gynaecologist and medical director of Parkway Fertility Centre at Mount Elizabeth Hospital added: "It is a life crisis that can be extremely frustrating and depressing."

It affects a couple's hopes, dreams and future plans and can lead to shock, disbelief, anger, sadness, blame and even marital discord and loss of self-esteem, Dr Nair said.

Infertility is the inability to conceive after a couple has actively tried to do so over the past 12 months, said Dr Ann Tan, a consultant obstetrician and gynaecologist at Women and Fetal Centre.

A Ministry of Health spokesman said it is estimated that 15 per cent of couples here are affected by infertility.

When a normal, healthy young couple have sexual intercourse, the chance of the woman getting pregnant is about 25 per cent.

After sex, sperm released by the male partner into the woman's vagina needs to travel up her fallopian tubes to fertilise the egg.

When fertilisation occurs, an embryo is formed, which then moves down into the woman's womb or uterus for implantation.

Most fertile when young

Women reach peak fertility in their 20s.

They are most fertile in the middle of their 28- to 30-day cycle.

Dr Stephen Chew, a senior consultant at the department of obstetrics and gynaecology at National University Hospital, said: "The woman's age is the most important factor determining fertility outcome."

Fertility in women falls by 4 to 8 per cent when they are between 25 and 29 years old; 15 to 19 per cent between 30 and 34 years old; 26 to 46 per cent between 35 and 39 years old; and 95 per cent by the time they hit 45 years of age.

Women stop producing eggs once they reach menopause and the average age when this occurs is 48 years.

Natural spontaneous conception is not possible after menopause.

Age no barrier for men

In contrast, men are fertile from puberty until their 70s, although their testosterone levels decline at a rate of about 1 per cent each year after the age of 30.

Sperm quality, quantity and sexual performance also go downhill as men get older.

Dr Jazlan Joosoph, a specialist in obstetrics & gynaecology at Raffles Hospital, said: "For men, the biological clock never stops. It only slows down.

"However, birth defects and genetic diseases have been associated with advanced paternal age, especially for fathers above the age of 50," Dr Jazlan said.

This is due to poorer sperm quality.

"Men, like women, are advised to start procreation at an early age," he added.

Other health factors

Various other factors can cause infertility.

In women, it can arise from one of three sites: the eggs, the fallopian tubes and the uterus.

Dr Nair said: "Fallopian tube problems include endometriosis, pelvic inflammatory disease and ectopic pregnancies which damage the tubes.

"A woman may also suffer from a misshapen or scarred womb, one that is physically unable to either have the embryo take seed or to nurture the developing foetus."

Dr Jazlan added: "Ovulatory problems are common causes of female infertility. Successful fertilisation or conception cannot occur if there is absence of egg production or if there are eggs of poor quality."

In men, infertility can be due to defects in sperm quality, its quantity or a sexual dysfunction such as premature ejaculation.

Dr Loh Seong Feei, the head and senior consultant at the department of reproductive medicine at KK Women's and Children's Hospital, said: "Many factors can cause the quality or quantity of sperm in the ejaculate to be low.

"Some common causes include genital tract infection and varicocele (widening of the veins along the cord that holds up a man's testicles).

"These factors can result in abnormally shaped sperm, which may not fertilise the egg, poor sperm motility such that sperm is unable to swim through the cervix to meet the egg, and low or zero sperm count."

Illnesses like mumps or cancer also affect fertility in men.

Lifestyle choices Professor P.C. Wong, the head and senior consultant at the reproductive endocrinology and infertility division in the obstetrics and gynaecology department at National University Hospital, said smoking affects sperm production, causing sperm quality and quantity to drop.

Dr Nair said that sperm concentration and motility fall by 19 per cent and 29 per cent respectively in men who smoke 10 to 20 cigarettes a day.

Besides smoking, other lifestyle factors also play a part in fertility.

Heavy drinking, over-exercise, anorexia and obesity contribute to infertility in men and women. Of course, infertility is never just one partner's problem.

Dr Nair said: "Knowing that you are less fertile and having to perform the sexual act can be demanding.

"This can affect spontaneity and lead to sexual difficulties or psychological stress that can strain the marriage or relationship."

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This article was first published in Mind Your Body, The Straits Times.