Optimal Timing Between Pregnancies

March 25, 2024

Pregnancy places significant strain on a person’s body and health. Ideally, patients should space their pregnancies out appropriately to mitigate health risks. Most of the data supports that providers should advise their patients to avoid an interpregnancy interval shorter than 6 monthsthe timing between pregnancies should be no less than 6 months, including a systematic review the WHO published in 2005, and that healthcare providers should advise their patients about interpregnancy intervals (IPIs) 1. Further studies on this matter seem to indicate that an interval of less than 18 months is associated with an elevated risk of adverse maternal, perinatal, infant and child outcomes1. The causal mechanism behind increased risk to birth outcomes related to short IPI is less clear1.  

One 2012 meta-analysis investigated the role of multiple proposed causes of adverse outcomes associated with shortened interpregnancy interval including potential maternal nutritional depletion, folate depletion, cervical insufficiency, vertical transmission of infections, suboptimal lactation, sibling competition, and abnormal remodeling of endometrial blood vessels2. Although some evidence indicated that folate depletion, vertical transmission of infections, and suboptimal lactation hypotheses may factors in causing adverse outcomes, no clear relationship could be established—more good quality evidence is required to draw a definitive causal explanation between any of these factors and adverse birth outcomes caused by short IPI2.  

While most of the data on this subject concerns shortened interpregnancy intervals, there is some evidence that longer timing between pregnancies may also adversely affect birth outcomes, including increasing risk of pre-eclampsia, reduced fetal birth weight and intrauterine fetal demise3. Furthermore, studies show that patients belonging to underserved communities experience these related adverse birth outcomes at disproportionately higher rates, despite risk-reduction interventions3. A literature review done in 2018 looked at rates of extremes in IPI and how they impact adverse birth outcomes in specific, at-risk populations3. Researchers looked at the data on risk-reduction interventions targeted at these populations and found that, while there was a higher incidence of shortened IPIs in most of the populations studied, the strength of association to adverse birth outcomes was modest3. This was likely due to confounders that are difficult to control for, such as variable access to prenatal care, maternal nutritional status, and marital status/access to a support network3. They also could not elucidate a biological causation for adverse birth outcomes related to extremes in IPIs. However, the review concluded that while the data couldn’t definitively support a strong relationship between inter-pregnancy interval and pregnancy outcomes, social and policy interventions supporting optimal timing between pregnancies may be “low-hanging fruit” for improving maternal and fetal morbidity and mortality overall, and particularly in higher-risk patients3.  

Overall, most research supports at least a moderate association between extremes in the timing between pregnancies, especially shorter IPIs, and adverse outcomes for both mother and baby1. Counseling on the importance of good quality post-partum birth control and the safety risks associated with waiting less than 18 months between pregnancies are important, accessible, and cost-effective “fourth trimester” interventions for improving outcomes1.  


  1. Bhattacharya S, Smith N. Pregnancy following Miscarriage: What is the Optimum Interpregnancy Interval? Women’s Health. 2011;7(2):139-141. doi:10.2217/WHE.11.2 
  1. Conde-Agudelo A, Rosas-Bermudez A, Castaño F, Norton MH. Effects of birth spacing on maternal, perinatal, infant, and child health: a systematic review of causal mechanisms. Stud Fam Plann. 2012 Jun;43(2):93-114. doi: 10.1111/j.1728-4465.2012.00308.x. PMID: 23175949. 
  1. Thagard, A.S., Napolitano, P.G., Bryant, A.S., 2018. The Role of Extremes in Interpregnancy Interval in Women at Increased Risk for Adverse Obstetric Outcomes Due to Health Disparities: A Literature Review. Current Women s Health Reviews 14, 242–250.. doi:10.2174/1573404813666170323154244