While multiple factors come into play when determining when it's time to have another baby, new research suggests that from a medical stand point at least, 12 to 18 months between delivery and conception is the safest interval.
The study, published in the journal JAMA Internal Medicine, found that becoming pregnant less than 12 months after welcoming a baby was associated with risk for women of all ages. Risk to mums were found only for those over 35, while risk to bubs were found for all women - and greatest for those aged 20-34.
"Although short intervals were associated with elevated risks of spontaneous preterm delivery and adverse fetal and infant outcomes for women of all ages, these risks were highest among younger women," the authors write.
While previous research has found that pregnancy spacing less than 18 months is associated with higher risk of adverse pregnancy outcomes, (for example a higher risk of premature birth), what remained unclear was whether the risks were higher for older mums compared to younger women.
To examine this, researchers examined data from almost 150,000 pregnancies in Canada.
Women over 35 who conceived six months after giving birth had a 1.2 per cent risk of maternal mortality or severe morbidity (complications such as organ failure, ICU admission). This decreased to 0.5 per cent for women who waited 18 months between babies.
In younger women, there was an 8.5 per cent risk of spontaneous premature birth for pregnancies spaced six months apart. The risk dropped to 3.7 per cent for pregnancies spaced 18 months apart.
The risk of spontaneous preterm labour was about six per cent for older women with pregnancies spaced six months apart, compared to 3.4 per cent for those who conceived 18 months after welcoming a baby.
"Our study found increased risks to both mother and infant when pregnancies are closely spaced, including for women older than 35," said the study's lead author Laura Schummers. "The findings for older women are particularly important, as older women tend to more closely space their pregnancies and often do so intentionally."
Adds co-author Dr Sonia Hernandez-Diaz: "Short pregnancy spacing might reflect unplanned pregnancies, particularly among young women." And whether the increased risks are due to our bodies not having time to recover if we conceive soon after delivering or to factors associated with unplanned pregnancies, like inadequate prenatal care, Dr Hernandez-Diaz notes that the recommendation might be the same "improve access to postpartum contraception, or abstain from unprotected sexual intercourse with a male partner following a birth."
The authors believe their findings may be particularly reassuring for older women. "Older mothers for the first time have excellent evidence to guide the spacing of their children," said senior author Dr. Wendy Norman. "Achieving that optimal one-year interval should be doable for many women, and is clearly worthwhile to reduce complication risks."
But there are some caveats.
"Women's decisions regarding the optimal timing and spacing of pregnancy are multifactorial, and modest increases in risk associated with short intervals may not outweigh other factors, including those unrelated to health outcomes, that women and families consider in spacing their pregnancies," the authors conclude.
Midwifery Advisor Ruth King of the Australian College of Midwives, who was not involved in the study, says of the findings: "Women's bodies are amazing and in the nine months of the pregnancy they have supported and nurtured a developing fetus. During this time their body has made several adaptations that will take time in the postnatal period to revert to the pre-pregnancy state."
As such, she notes, waiting for a period of time between pregnancies allows the woman's body to nourish the newborn as well as to recover from the adaptations so as to be in the best health for the next pregnancy. "Some women may have events occur in their pregnancy (such as significant perineal trauma or a c-section) that will result in advice being given to delay pregnancy due to additional healing being required," Ms King says.
She also highlights that the study reflects that shorter periods between pregnancies could be related to lack of information or access to contraception in the postnatal period. "The advice regarding postnatal contraception typically occurs when women are being discharged from hospital along with a raft of other issues and topics for them to consider," Ms King says. "They are then required to go to their GP for a follow up appointment where they can address contraception. The risk here is that women fall through the gaps by either not attending the GP appointment or forgetting to ask about their options."
Ms King explains that it's important that topics such as postnatal contraception are also raised as part of a mother's antenatal care when discussing breastfeeding. "Women are advised that whilst breastfeeding may result in amenorrhea (cessation of periods/bleeding) it is not a 100 per cent proof against getting pregnant and that women should be sure to be using a contraceptive should they not want to conceive in a short period of time."
"Midwives who work in a continuity of Care model cover postnatal contraception with the women as part of their routine postnatal care and so women benefit from having a single point of contact for advice and information," she says.