New research shows that if you are considering having another child, you may be well advised to wait longer than two years.

The ideal spacing between children was always thought to be two years. The most recent study puts that figure at three to five years Deciding when to go for number two (or three, four or five) is a complex matter for parents.

As so many Irish women are starting families later in life, there's a temptation to have a number of children in quick succession, before the 40s loom. There are three main factors to consider - the health of the mother, the health of the child and the ability of both parents and the other children to cope with the new arrival.

Until recently, it was recommended that mothers wait two years between giving birth and conceiving again. This was based on a 1999 study carried out by the US Centre for Disease Control and Prevention which studied the births of 173,205 children from Utah between 1989 and 1996. Researchers found that a baby conceived less than 18 months after a sibling's birth was 40 per cent more likely to be premature or have a low birthweight than one born after an 18-month or 23-month delay.

According to the same study, babies conceived more than two years after the previous child were twice as likely to be underweight and 70 per cent more likely to be born prematurely.

From the mother's perspective, this 18- to 23-month gap between children was thought to be optimal because she has time to replenish her nutrient stores, but her body is still "primed" for pregnancy.

In October last year, the Population Information Program at the John Hopkins Centre in Maryland released the results of a study of more than 430,000 pregnancies in 18 countries. Children born three to five years after the previous child are about 2.5 times more likely to survive to age five than children born less than two years after the previous child, according to the report, Birth Spacing: Three to Five Saves Lives.

The study suggests that waiting longer than the previously recommended two-year gap between births gives infants and children a better chance of survival.

Communication campaigns in several countries have already begun promoting three-year spacing to raise awareness of the benefits of birth spacing.

Why are short birth intervals riskier for mothers and children? Researchers suspect that mothers who give birth frequently may not have time to restore their own nutritional reserves or breast milk. Also, children close in age are more likely to compete for food and other resources. Competition for food may not be an issue in the developed world, but competition for attention may be.

Of course, many women have children close together without complication. For those with a number of children close in age there are disadvantages. Children may lose out in terms of one-on-one time with parents and parents' lives are significantly disrupted during the baby years. There are advantages, too, however.

Emma Percival, a mother of three children under the age of four from Dalkey in Dublin, has no regrets about having her children so close in age.

"I really think that we made the right decision to have another baby rather than leave it a few years. For us, we just couldn't face getting out of baby mode and then have to go back to sleepless nights in a few years - we'd rather do it now when we're already wrecked and have little social life. Also, what's another little one in the fun-filled chaos of this house!"

She does have one word of warning for parents about to take the plunge, though. "One of the disadvantages is that you don't get to spend as much individual time with each of them, but I think the company of their siblings is a gift to them and they are more likely to really play together when there is a smaller age gap. Through each other, they learn to share, to have patience, responsibility and to look out for one another."

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