Health of women around the time of conception, once a neglected topic, is now a focus of increasing interest, reflected in several reports from national1, 2 and international health agencies.3, 4 This Series on preconception health makes the case for preconception health as a key determinant of pregnancy success and next generation health, drawing on evidence across clinical, biological, social, and policy fields. In this report, we follow three lines of enquiry. First, we review the evidence linking preconception health, particularly nutritional status, to pregnancy and birth outcomes, including analysis of the few cohort studies to have recruited women before pregnancy in low, middle, and high-income countries (appendix),5, 6, 7, 8 and we survey data on the nutrition of a nationally representative sample of women in a high-income country (the UK).9 Using these data, we assess how well women are prepared, in health terms, for pregnancy. Second, we assess the extent to which intervention during pregnancy can mitigate the effect of preconception risk behaviours by reviewing systematic reviews of dietary and lifestyle interventions that started in pregnancy (appendix). Third, efforts to improve preconception health can be aimed at a population level, irrespective of any pregnancy planning, and can be targeted more specifically at women who are planning for pregnancy. We therefore review what is known about the extent of planning for pregnancy, including new data from a low-income country (Malawi) on how to measure pregnancy planning.10 A host of social, medical, and environmental conditions can influence pregnancy outcomes, including genetic disorders, pre-existing physical and mental health conditions, teratogens, and domestic abuse to name a few. We recognise their importance, but review of these conditions is outside the scope of this paper. The importance of the father's preconception health is addressed in the second Series paper whereas the third Series paper reviews the targeting of intervention strategies to improve preconception health.
Key messages
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Health before conception is strongly linked to the outcome of pregnancy; life-course research pin-points the preconception period as crucial for health across generations.
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The preconception period should be redefined according to (1) the biological perspective—days to weeks before embryo development, (2) the individual perspective—a conscious intention to conceive, typically weeks to months before pregnancy occurs, and (3) the public health perspective—longer periods of months or years to address preconception risk factors, such as diet and obesity.
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Many women of reproductive age in low, middle, and high-income countries will not be prepared nutritionally for pregnancy.
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Micronutrient supplementation started in pregnancy can correct important maternal nutrient deficiencies, but it is not sufficient to fundamentally improve child health; dietary interventions in pregnancy can limit weight gain, but they are also insufficient in improving pregnancy outcomes.
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The preconception period presents a period of special opportunity for intervention; the rationale is based on lifecourse epidemiology, developmental (embryo) programming around the time of conception, maternal motivation, and disappointment with interventions starting in pregnancy.
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Improved measurement shows that pregnancy planning is more common than previously recognised in low, middle, and high-income countries.
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Identification of people contemplating pregnancy provides a window of opportunity to improve health before conception, while population-level initiatives to reduce the determinants of preconception risks, such as obesity and smoking, irrespective of pregnancy planning, are essential to improve outcomes.