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Risks of shorter interpregnancy intervals differ by maternal age

By Melanie Hinze
Short interpregnancy intervals are associated with increased risks for adverse pregnancy outcomes regardless of maternal age; however, the specific risks vary by maternal age, new research published in JAMA Internal Medicine suggests.

A Canadian population­-based cohort study of 148,544 pregnancies compared the risk of adverse pregnancy outcomes three­, six­, nine­, and 12 ­month interpregnancy intervals with those at 18­-month intervals according to maternal age at index birth (20 to 34 years vs 35 years and older).

When six­-month interpregnancy intervals were compared with 18­ month intervals, adverse fetal and infant outcomes and preterm delivery were increased in mothers aged 20 to 34 years but not in those aged 35 years or over. Conversely, maternal mortality and severe morbidity risks, such as blood transfusion of more than three units, intensive care unit admission and organ failure, were increased in women aged 35 years or older, but not in those aged 20 to 34 years.

‘Current clinical and public health recommendations suggest a minimum interpregnancy interval of 18 months, and some suggest a range from 18 to 60 months,’ the researchers wrote.

However, they said their findings suggested that the optimal interpregnancy interval was closer to 18 months.

In an accompanying commentary, Professor Stephanie Teal and Dr Jeanelle Sheeder of the University of Colorado’s Department of Obstetrics and Gynecology, USA, said that although the findings seemed to indicate that clinicians should encourage women 35 years or older to avoid rapid repeat pregnancy, the situation was complicated by the decline in fertility beginning in the mid­-30s and accelerating rapidly through the 40s.

‘Also, while fetal and infant risks for younger women continue to decrease with increased birth spacing up to 24 months, these risks do not diminish significantly for the older cohort with longer birth spacing,’ they wrote. ‘Thus, even with the moderate increased risk of severe maternal outcomes identified [in this study] shorter interpregnancy intervals may be a rational choice.’

They recommended that clinicians use patient­-centred counselling and shared decision­-making strategies respecting women’s desires for pregnancy, possibly at short intervals in women 35 years or older, and adequately discuss fetal, infant and maternal risks in this context.
JAMA Intern Med 2018; doi: 10.1001/jamainternmed.2018.4696.
JAMA Intern Med 2018; doi: 10.1001/jamainternmed.2018.4734.