If you use a fertility awareness method (FAM) for family planning, you know you can use your body’s fertility biomarkers to space pregnancies. Of course, some of the spacing may be taken out of your hands if, for example, breastfeeding causes a delay in your return of fertility for a full year or even longer, as some women experience. For other women, even while breastfeeding, their period returns like clockwork twelve or even fewer weeks postpartum (hence most methods’ requirement that you start charting six weeks after birth). So, whether you’re cycling regularly, cycling irregularly, or charting as you await the return of your fertility, you know you can use FAMs to reliably avoid pregnancy— but how long do you need to? For the safety of both mom and baby, how long should you wait after giving birth before conceiving again?
Where did the two year interpregnancy interval recommendation come from?
Many women have been counseled by their healthcare providers to space pregnancies two or more years apart. But where does that recommendation come from? And is it evidence-based? The recommendation seems to come from a 2005 report by the World Health Organization (WHO) which specifically noted that an interpregnancy interval (IPI)–the time between the birth of one child to the conception of the next child–of less than 18 months was associated with increased infant mortality, low birth weight, and preterm delivery [1]. An IPI between 18-27 months may also have increased risk, but the document acknowledged that evidence for this was limited. The final recommendation of waiting at least two years was made with the consideration that saying “two years” is simpler than saying “18 months” or “27 months” when making recommendations [1].
However, the report also contained an important preamble emphasizing that family planning is a very personal decision with many factors to take into account:
Individuals and couples should consider health risks and benefits along with other circumstances such as their age, fecundity, fertility aspirations, access to health services, child-rearing support, social and economic circumstances, and personal preferences in making choices for the timing of the next pregnancy [1].
Issues with the WHO recommendation
The main issue with the WHO’s recommendation of waiting two years between pregnancies seems to be that the data used to inform this recommendation comes largely from low to middle-income countries. Pregnant women with less access to adequate nutrition and health resources may indeed face a greater risk of experiencing, or their newborn experiencing, a medical complication during pregnancy or birth when having children relatively close together in age. However, adequate access to food and medical care is not a major obstacle for all women, especially in higher income countries, so this recommendation lacks universal application.
Additionally, the WHO recommendation does not take maternal age into account. In addition to age being an important factor in fertility, experiencing pregnancy over the age of 35 is associated with greater risk of morbidity– particularly higher C-section rates. Couples for whom age is an important factor, such as couples who started having children later in life or couples hoping to have a large family may want to space pregnancies closer together to maximize their years of increased fertility–what advice the WHO would give to such couples with these circumstances and desires is unclear.
Recent research from Sweden doesn’t back up the two year IPI recommendation
In the United States, the American College of Obstetricians and Gynecologists (ACOG) also cautions that pregnancies less than 18 months apart are associated with an increase in adverse outcomes, but ACOG notes that recent studies call this timeframe into question. One such study released last year and conducted in Sweden found that waiting more than 24 months between pregnancies was associated with an increase in maternal and neonatal morbidity [2].
Who and what did the Swedish researchers study?
The Swedish study analyzed birth data between 1997 and 2017 from multiple Swedish national registers, including the Swedish Medical Birth Register. The study excluded women who delivered their first baby via Cesarean section, women whose IPI was greater than five years, and cases with missing information. Nonetheless, the study still included over 300,000 mothers.
Swedish researchers studied morbidity
Researchers assessed neonatal and maternal morbidity in relation to IPI, but what does that mean? “Morbidity” refers to developing some sort of medical condition during a specific timeframe; in this case, morbidity during pregnancy or immedi ately postpartum was studied. Mortality (maternal death) and severe maternal morbidities were measured in the study, including sepsis, eclampsia, surgery, unscheduled C-section, blood clots, and severe perineal tears (severe morbidities). Moderate maternal morbidities included postpartum hemorrhage, preeclampsia, gestational diabetes, infection, forceps use, vacuum extractor use, planned C-section, and episiotomy. Severe neonatal morbidities included stillbirth, need for ventilation, hypoglycemia, birth trauma, low birth weight and premature birth. Moderate neonatal morbidities included jaundice, macrosomia (large birth weight), and hematoma.
Lowest maternal and neonatal morbidity rate was found with IPI of 6-11 months
The researchers found that the risk of severe morbidity was lowest for both mothers and infants with an IPI of 6-11 months and higher when the IPI was 24-29 months or more.
- Severe maternal morbidity: 4.7% at <6 months, 4.5% at 6-11 months, 4.66% at 12-17 months, 4.98% at 18-23 months, 5.6% at >24 months.
- Moderate maternal morbidity: 12.3% at <6 months, 12.62% at 6-11 months, 13.26% at 12-17 months, 14.38% at 18-23 months, 16.33% at >24 months.
- Severe neonatal morbidity: 4.75% at <6 months, 4.00% at 6-11 months, 3.99% at 12-17 months, 4.06% at 18-23 months, 4.61% at >24 months.
- Moderate neonatal morbidity: 11.21% at <6 months, 9.64% at 6-11 months, 9.40% at 12-17 months, 9.60% at 18-23 months, 10.32% at >24 months.
If IPI doesn’t impact maternal and neonatal morbidity, what does?
While the study sought to answer the question of whether there is an association between morbidity and IPI length, the figures in the final report suggest that IPI length does not seem to have a dramatic effect on a person’s chances of developing a comorbidity during pregnancy or birth. Instead, many other factors appear to be more important when it comes to developing a pregnancy or birth-related complication. This is good news for parents wanting to have children closer together, as the odds of having morbidities related to pregnancy and birth with a short IPI are similar or even less than they would be if parents waited two years. Furthermore, the incidence of morbidities at longer IPIs was typically within a couple of percentage points of the incidence at shorter IPIs, suggesting that couples who still want to wait a couple of years between pregnancies are only at a slightly increased risk of complications.
The study adjusted for other potential confounding factors including education, body mass index (BMI), immigration status, smoking, use of in vitro fertilization (IVF), little prenatal care, medical problems prior to first birth, and complications in the first birth. Morbidity was lower after this adjustment, suggesting that the specific health characteristics of the mother, rather than IPI, are a major driver of maternal and infant morbidity. The study researchers believe their results to be generalizable to other high-resource countries where nutrition and health care are readily available.
Other research corroborates the Swedish study
An Australian study from 2021 followed 1.2 million women in high-income countries and found that an IPI of less than six months posed no greater risk to experiencing adverse birth outcomes than an IPI of 18-23 months [3]. This seems to follow the trend observed in the Swedish study in which the incidence of severe morbidity for both mothers and newborns in the <6 month and 18-23 month IPI ranges were both within a single percentage point of each other. This study also noted that an IPI of more than 5 years had an increased risk of adverse birth outcomes. These results dovetailed with the conclusions of the Swedish study which found that longer IPIs tended to be associated with greater morbidity [3].
The bottom line
So, do you need to wait two years after your last pregnancy to conceive again? Not if you have access to healthcare and adequate nutrition, according to recent research. If your fertility is returning or has returned, you don’t have any outstanding unresolved health complications from your previous birth or other medical contraindications to pregnancy as determined by your healthcare provider, and you’re ready to try again, then go for it! Best of all, if you chart with a FAM, you can utilize your body’s own data to target your fertile window and increase your chances of successfully conceiving.
References:
[1] World Health Organization. The World Health Report 2005: Make every mother and child count. (2005). The World Health Report 2005. Make every mother and child count (who.int) [2] Mühlrad, H., Björkegren, E., Haraldson, P. et al. Interpregnancy interval and maternal and neonatal morbidity: a nationwide cohort study. Sci Rep 12, 17402 (2022). https://doi.org/10.1038/s41598-022-22290-1 [3] Tessema G, et al. “Interpregnancy intervals and adverse birth outcomes in high-income countries: An international cohort study.” PLOS ONE, 2021; 16 (7): e0255000 DOI: 10.1371/journal.pone.0255000Additional Reading:
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