Getting pregnant again less than 12 months after the delivery of a child is associated with risks for women of all ages, according to researchers.
In a study published in JAMA Internal Medicine, researchers found that 12 to 18 months seems to be the ideal length of time between giving birth and getting pregnant again.
“Our study found increased risks to both mother and infant when pregnancies are closely spaced”
But getting pregnant less than 12 months was associated with risks for women of all ages, according to study by the University of British Columbia and the Harvard T.H. Chan School of Public Health.
Risks to the mother were found only for women over the age of 35, while risks to the infant were found for all women, but were greatest for women between the ages of 20-34, said the reseachers.
The study is the most extensive evaluation of how the role of pregnancy spacing could be impacted by maternal age.
It is also the first investigation of pregnancy spacing and maternal mortality or severe morbidity – rare but life-threatening complications of pregnancy, labour and delivery – in a high-income country.
“Older mothers for the first time have excellent evidence to guide the spacing of their children”
For the study, researchers examined the relationship between risks for mothers and babies associated with pregnancy spacing among 148,544 pregnancies in British Columbia.
The data was pulled together from birth records, billing codes, hospital admission data, prescription data for infertility information, and census records.
Among women over 35 who conceived six months after a previous birth, the researchers found a 1.2% risk (12 cases per 1,000 pregnancies) of maternal mortality or severe morbidity.
Waiting 18 months between pregnancies, however, reduced the risk to 0.5% (five cases per 1,000 pregnancies).
For younger women, the researchers found an 8.5% risk (85 cases per 1,000 pregnancies) of spontaneous preterm birth – delivery before 37 weeks of pregnancy after labour that started on its own, for pregnancies spaced at six months.
For younger women who waited 18 months between pregnancies, however, the risk dropped to 3.7% (37 cases per 1,000 pregnancies).
Among older women, the risk of spontaneous preterm labour was about 6% (60 cases per 1,000 pregnancies) at the six-month interval, compared to 3.4% (34 cases per 1,000) at the 18-month interval.
“This is useful research and builds on previous research into birth spacing”
Although the causes of poor pregnancy outcomes at short intervals among older and younger women were not examined in this study, the findings suggest different risk profiles for each age group.
Lead study author Laura Schummers, a postdoctoral fellow, said: “Our study found increased risks to both mother and infant when pregnancies are closely spaced, including for women older than 35.
“The findings for older women are particularly important, as older women tend to more closely space their pregnancies and often do so intentionally,” she said.
Senior author Dr Wendy Norman suggested the findings of a shorter optimal interval were encouraging for women over 35 who are planning their families.
“Older mothers for the first time have excellent evidence to guide the spacing of their children,” said Dr Norman.
She added: “Achieving that optimal one-year interval should be doable for many women, and is clearly worthwhile to reduce complication risks.”
Mandy Forrester, head of quality and standards at the Royal College of Midwives, said: “This is useful research and builds on previous research into birth spacing.
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“Ultimately, it will be a woman’s choice whatever age they are about how long they leave between their pregnancies,” said Ms Forrester.
“What is important is that they are aware of the evidence around birth spacing and that they make their choice armed with the right information,” she said. “Health professionals will always support a woman in her choice, which will be about what is right for them and their pregnancy.
She added: “Women do though also need access to contraceptive advice to allow them to space their births if that is their choice.
“In the UK, specialist family planning service provision is patchy with GPs frequently offering only oral contraception,” she said. “Specialist services should be available for all women.”