Women 'should leave at least a year between pregnancies'

Tuesday October 30 2018

"Conceiving again too soon increases the risk of premature labour, stillbirth and even maternal death," reports the Mail Online.

A new study advises women to leave 12 to 18 months between giving birth and getting pregnant again to reduce health risks to mother and baby.

Current guidance from the World Health Organization recommends a gap of 18 to 24 months between pregnancies.

The study looked at nearly 150,000 pregnancies in Canada to investigate the link between pregnancy gap and the risk of pregnancy complications.

The researchers wanted to see if this link applied regardless of the mother's age.

Researchers found that gaps of 12 months or less between pregnancies were linked with a small increased risk of premature births, smaller babies, and the mother or baby dying.

The links were broadly the same for older and younger women, but weren't so consistent.

All of the complications reported in the study were rare, affecting less than 5% of all pregnancies. Most of the women had healthy births and pregnancies.

It's not possible to prove that a shorter pregnancy interval has directly caused the complications found in the study.

Other factors associated with shorter intervals, such as lifestyle factors or prior pregnancy problems, could have played a role.

The study's findings may inform general guidance, but it's not always possible to plan for longer pregnancy intervals.

Women who fall pregnant after less than 18 months shouldn't be too concerned, as the risk to them still remains low.

Where did the story come from?

The study was conducted by researchers from the Harvard T. H. Chan School of Public Health in the US and the University of British Columbia in Canada.

Some of the researchers received funding from various sources, including the Eunice Kennedy Shriver National Institute of Child Health and Human Development, the US National Institutes of Health, and the Canadian Institutes of Health Research.

The study was published in the journal JAMA Internal Medicine and is free to read online.

The media generally reported the story accurately. But it's a shame the news stories didn't make it clearer that the chance of these pregnancy complications is small, regardless of how long you wait between pregnancies.

What kind of research was this?

This study used data from a population-based Canadian cohort study.

Researchers wanted to see if shorter pregnancy intervals were associated with an increased risk of complications, particularly among older women.

Such studies are useful for looking at links, but can't prove that the pregnancy interval was directly responsible for the pregnancy complications.

Other factors associated with shorter intervals (for example, complications in previous pregnancies) may have played a role.

What did the research involve?

This study used the data from the British Columbia Perinatal Data Registry, which contains maternity and newborn data for nearly all births in British Columbia.

The researchers looked for women who had at least 2 single pregnancies between 2004 and 2014.

The registry only contains data for pregnancies that continued to at least 20 weeks, so they also used hospital and medical records to look for earlier miscarriages.

Pregnancy interval was defined as the number of months between the first birth and conception of the following pregnancy (as estimated from last menstrual period and ultrasound scans).

The researchers looked at the association between this interval and pregnancy or birth complications, dividing the women according to their age at the first birth: younger than 20, 20 to 34 and 35 and older.

The researchers adjusted for various potential confounders, including sociodemographic factors, obesity and infertility treatment.

What were the basic results?

The total sample included 123,122 mothers and 148,544 pregnancies. More than 80% of pregnancies were among women aged 20 to 34 years, with 5% in women under 20 and 12% in women over 35.

Only around 5% of all women had a pregnancy interval of less than 6 months.

Compared with women aged 20 to 34, women over 35 were just slightly more likely to have a pregnancy interval of 6 to 11 months (18% compared with 17%) or 12 to 17 months (25% compared with 23%).

Lower sociodemographic status, smoking in pregnancy and less antenatal care were associated with the shortest pregnancy intervals.

For women overall, pregnancy intervals of 9 to 12 months or less were associated with a small increased risk of the following complications, compared with a pregnancy interval of at least 18 months:

  • small baby
  • premature birth
  • severe foetal or newborn complications (a combined outcome looking at extremely low birthweight or prematurity, stillbirth or infant death)
  • severe maternal illness or death

When looking by specific age group, either 20 to 34 or 35 or older, the same links were generally seen, but they weren't so consistent.

For example, a shorter pregnancy interval was linked with maternal illness for older women, but there wasn't a clear link for younger women.

Meanwhile, a shorter interval was linked to small babies in young women, but the link was no longer clear for older women.

But it's difficult to know whether these inconsistencies may be the result of smaller numbers.

The overall association for all women is likely to be the most reliable analysis.

How did the researchers interpret the results?

The researchers concluded that overall, "The findings of this study suggest that short pregnancy intervals are associated with increased risks for adverse pregnancy outcomes for women of all ages."

Conclusion

This study gives a valuable look at whether pregnancy interval is associated with pregnancy or birth complications, and whether this varies by maternal age.

The study's strengths are that it looked at a large number of women and used registry data and medical records, which should be reliable.

It generally found a small increased risk of pregnancy or newborn complications for women who got pregnant again within 18 months. This tended to be the case regardless of the woman's age.

But there are a few important points to put this into context.

Pregnancy complications were, on the whole, rare. So even for women with shorter pregnancy intervals of 12 months or less, these complications were still rare.

The vast majority of women have healthy pregnancies and babies regardless of pregnancy interval.

This study can't prove that the pregnancy interval was directly responsible for the pregnancy complications.

The researchers tried to take into account potential confounders, but it's still difficult to rule out the possibility that factors such as the mother's income, lifestyle, reproductive history or previous pregnancy complications could be behind the links.

This study only looked at Canadian pregnancies. We can't be sure that the findings would apply to women in the UK.

The researchers hope that this evidence will help guide health professionals giving pregnancy counselling, supporting advice that leaving an interval of more than 12 months between pregnancies is best.

But it may not always be possible for women to follow this advice, either because of an unplanned pregnancy or other personal factors.

It's important that women are reassured that while there is a link between shorter pregnancy intervals and an increased risk of complications, this risk remains small.

Analysis by Bazian
Edited by NHS Website