Having children is a natural and significant step after marriage. Couples further their love and commitment to each other when they experience parenthood.

However, views on pregnancy and parenthood may vary. Many Singaporeans are unwilling to embrace parenthood, or they delay having children, citing the high cost of living, lack of support and time, and a reluctance to compromise on their lifestyles as the reasons.

They may consider fertility as a tap and think conception happens at will. The fact is that fertility declines with age and the biological clock in both the man and the woman ticks away every day. An infant girl has about 1 million eggs at birth. This declines to about 40,000 when she reaches puberty.

A woman's ability to conceive is reduced after 30 and it drops precipitously after 40. Male fertility too declines after 40, when the quantity and quality of sperm deteriorate. My patient, Mrs B, learnt the truth the hard way. Her story is one of despair but, finally, joy.

"Doc," she said, "when we got married four years ago, parenthood was never on our minds. I am a banker and he is an engineer. We were chasing our dreams. We wanted to climb up the corporate ladder as fast as we could. Besides, we were not willing to give up our lifestyles. Having a baby meant the end of cosy tete-a-tetes, candle-light dinners and holidays together."

On their third wedding anniversary, they decided to start a family. By then, Mrs B was 33 and her husband 38.

"I thought it would be easy," she recalled. "We were both convinced that it would happen quickly. After all, we were both very goal-oriented people. So we were puzzled when six months went by and nothing happened. We told ourselves that it would happen when the time was right.

"After a year of trying, I began to feel the stress. I was moody, irritable and short tempered. I was always in tears when my menses came. This affected our relationship. I no longer enjoyed sex and started to lose interest in it."

On her first consultation, Mrs B looked slightly withdrawn and depressed. She was overweight, with a BMI of 28 (ideally it should be between 20 and 23). She attributed this to frequent overseas trips and the junk food she consumed. Her menstrual cycles were irregular, occurring once in 23 to 38 days. There were no menstrual cramps or vaginal discharge. Her husband was a smoker but appeared healthy otherwise.

"My husband and I work long hours and I have to make overseas trips frequently," she said.

They barely had time for sex, averaging once a week. I told her that accurate timing for sexual intercourse was important for conception.

The egg, released in the middle of a 28-day cycle, lives for 24-36 hours. In Mrs B's case, her ovulation might have been infrequent or compromised as she had irregular cycles. Ovulation can be detected in various ways. Basal Body Temperature (BBT) charting is the simplest method of estimating the time of ovulation. It is done by charting daily oral temperatures using a special thermometer. Although normal temperature is stated to be around 36.5 deg C, slight variations occur.

The temperature is lower in the first part of the menstrual cycle than in the last two weeks. The shift from lower to higher temperatures occurs around the time of ovulation.

A few days before ovulation, secretions from the neck of the womb (the cervix) start to flow into the vagina. Fertile time begins when a woman feels a sensation of discharge from the vagina. The mucus becomes thicker and more like raw egg white as ovulation approaches. The fertile mucus protects sperm from acid secretions in the vagina, nourishes and keeps sperm alive for several days.

When one is about to ovulate, the body produces a large quantity of a hormone called LH. This can be detected in the urine using an ovulation kit.

As Mrs B was overweight, she was put on a weight reduction programme. Her cycle became more regular as a result. Her husband was also advised to quit smoking to improve the quality and quantity of his sperm.

After a few months of charting the BBT and observing the cervical mucus, the couple took a short holiday.

"We went somewhere quiet where I would not be tempted to shop. We had a great time together. We were relaxed and didn't have to bother about household chores. And I conceived," said Mrs B who was beaming when I confirmed her pregnancy.

The couple now have two children.

Dr Peter Chew is a senior consultant gynaecologist and obstetrician at Gleneagles Medical Centre. He is the founder chairman of aLife (www.alife.org.sg), a charitable organisation with a mission to nurture and promote healthy family life.

This article was first published in Mind Your Body, The Straits Times, on April 30, 2008.