When Ms Flora Lim tied the knot at the age of 27, having children was not one of her immediate priorities.

In fact, she had planned to have her first child when she turns 35.

"I believe that most couples have this very ideal five-year or 10-year plan... that we get married and enjoy a few years of personal time before eventually having kids," said the social media director, now 31.

But a fertility health check with her 32-year-old husband in July last year upended her plans.

The check, done at Thomson Fertility Centre, showed that Ms Lim had endometriosis, a condition where the cells of the uterine lining are deposited outside the uterus.

About 30 per cent to 40 per cent of women with endometriosis are infertile, making it one of the leading causes of infertility among women in Singapore.

That was when she and her husband decided to try for a baby earlier. "Since discovering that it might not be that easy to have children, we adjusted our life plans to start trying earlier so that we can consider in-vitro fertilisation or other treatment options in time to come if necessary," she said.

After months of trying, Ms Lim is now eight months pregnant with a baby boy. She credits the early medical intervention for allowing her to make informed decisions about fertility planning.

SCREEN FOR FERTILITY ISSUES

Ms Lim and her husband are among the estimated one in six couples here with fertility problems, say experts.

Infertility is defined as the inability to get pregnant after a year of trying or, if a woman is 35 or older , after six months of trying.

Apart from endometriosis, common causes of infertility in women include polycystic ovarian syndrome, which can affect normal ovulation, and uterine fibroids that can hinder the successful implantation of an embryo in the womb.

Men are not spared either. A condition called varicocele can result in decreased sperm production and quality. This can then affect the chances of conception.

Gynaecologists The Straits Times spoke to advised couples who are looking to have children to consider screening for such health conditions that could affect their chances of natural conception.

Dr Loh Seong Feei, medical director at the Thomson Fertility Centre, said: "Everyone thinking of conceiving should go for a fertility health check and screen for some of the common health issues (that could affect fertility). The checks are harmless and relatively non-invasive."

The health check would usually consist of two clinic visits. The couple first undergoes a screening consultation with a fertility doctor. This will include an examination of the couple's medical history. An ultrasound scan and hormone blood test are done for the wife, and a semen analysis for the husband.

A check with several fertility centres in Singapore found that such fertility health screening costs from $450 to $600.

Dr Ann Tan, medical director at Mount Elizabeth Fertility Centre, said that such checks are important to sieve out underlying health issues that might affect fertility.

"You can't really see the issues that might affect fertility. A man might appear physically fit and healthy but it doesn't mean his sperm parameters are within a normal range," she added.

Women above 35 are strongly advised to undergo a fertility health check with their partners as the quality and number of eggs begin to decline drastically after that age.

Gynaecologist Roland Chieng, director at Virtus Fertility Centre, said: "The age of 35 is when the fertility decline becomes obvious - it seems to be the age when the chances of getting pregnant start to drop."

The success rate is about 84 per cent for women aged 30 who have been trying for a year, but this falls to about 78 per cent for women between 35 and 40. About 30 per cent of women aged 35 and older take a year or more to conceive naturally.

Women who regularly experience menstrual cramps, abnormal or heavy menstrual bleeding and pelvic pain should consult their gynaecologist and arrange for a fertility screening as these could be symptoms of more severe underlying fertility issues.

Apart from signing up for fertility health checks, couples looking to conceive are encouraged to lead healthy lifestyles, have adequate sleep and consume a well-balanced diet. They should also avoid smoking, consuming alcohol excessively and prolonged exposure to environmental pollutants, say doctors.