If you're thinking of having another child, wait for at least a year.

This is because optimal birth spacing benefits both mother and child, said Dr Beh Suan Tiong, president of the Obstetrical & Gynaecological Society of Singapore (OGSS).

Optimal birth spacing means allowing for an interval between births that results in the best health and social outcomes for the family.

'It gives women time for their bodies to recover from a birth and return to a stable nutritional status after the previous pregnancy,' said Dr Beh, who is also an obstetrician and gynaecologist at Thomson Medical Centre.

Thus, conceiving another child within six months of delivery poses health risks. For example, the mother may suffer from anaemia due to a lack of iron, which is essential in red blood cells, he said.

Most Singaporean women space their births optimally between one and three years. That, he said, is good news.

Of the 387 mothers polled in the first Birth Spacing Saves Lives survey by Bayer Schering Pharma in Singapore between June and September last year, 46 per cent practised optimal birth spacing of one to three years.

Half of them had a gap of one to two years, while the other half waited two to three years.

However, one in 10 mothers fell short of this optimal range. They either had their next child after a long interval of several years or had another child too soon after a birth.

This is not the only research that recommends optimal birth spacing. A 2006 study published in the Journal Of The American Medical Association also showed that short intervals of less than a year between births are linked to several adverse foetal outcomes.

This includes miscarriages, slow foetal development, premature babies and babies with low birth weights.

Besides, it can be tough on the mother as the older child is still very dependent on her for daily tasks like eating, said Dr Beh.

On the other hand, waiting too long - five years or more - may give rise to the problem of decreased fertility, particularly if the woman is already in her 30s.

Older women are also at higher risk of ailments like high blood pressure and diabetes during pregnancy.

Effective birth control methods are central to birth spacing.

In Singapore, the condom is the most commonly used birth control method, followed by the oral contraceptive pill.

Another option is the intra-uterine system (IUS) - a device placed in the uterus to obstruct the embryo from implanting in the endometrium or uterine wall lining.

The IUS also releases hormones that thin the endometrium and thickens the cervical mucus - factors that help prevent pregnancies.

However, some women shy away from the more invasive - though more effective - methods as they believe they may have difficulties getting pregnant again.

'Many people are afraid to use contraceptives other than condoms,' said Dr Christopher Ng, obstetrician and gynaecologist at Camden Medical Centre.

'Many of them think that using the oral pill or the IUS will delay fertility,' he said, adding that such worries are unfounded.

Said Dr Ng: 'In fact, once you stop taking the pill or once the IUS is removed, there is no delay in fertility return.'

This article was first published in Mind Your Body, The Straits Times on Jan 22, 2009.