The associations of birth intervals with small-for-gestational-age,preterm, and neonatal and infant mortality: a meta-analysis

Background

Short and long birth intervals have previously been linked to adverse neonatal outcomes. However, much of the existing literature uses cross-sectional studies, from which deriving causal inference is complex. We examine the association between short/long birth intervals and adverse neonatal outcomes by calculating and meta-analyzing associations using original data from cohort studies conducted in low-and middle-income countries (LMIC).

Methods

We identified five cohort studies. Adjusted odds ratios (aOR) were calculated for each study, with birth interval as the exposure and small-for-gestational-age (SGA) and/or preterm birth, and neonatal and infant mortality as outcomes. The associations were controlled for potential confounders and meta-analyzed.

Results

Birth interval of shorter than 18 months had statistically significant increased odds of SGA (pooled aOR: 1.51, 95% CI: 1.31-1.75), preterm (pooled aOR: 1.58, 95% CI: 1.19-2.10) and infant mortality (pooled aOR: 1.83, 95% CI: 1.19-2.81) after controlling for potential confounding factors (reference 36-<60 months). It was also significantly associated with term-SGA, preterm-appropriate-for-gestational-age, and preterm-SGA. Birth interval over 60 months had increased risk of SGA (pooled aOR: 1.22, 95% CI: 1.07-1.39) and term-SGA (pooled aOR: 1.14, 95% CI: 1.03-1.27), but was not associated with other outcomes.

Conclusions

Birth intervals shorter than 18 months are significantly associated with SGA, preterm birth and death in the first year of life. Lack of access to family planning interventions thus contributes to the burden of adverse birth outcomes and infant mortality in LMICs. Programs and policies must assess ways to provide equitable access to reproductive health interventions to mothers before or soon after delivering a child, but also address underlying socioeconomic factors that may modify and worsen the effect of short intervals.

     

Myocarditis and pericarditis: Case definition and guidelines for data collection,analysis, and presentation of immunization safety data

Myocarditis and/or pericarditis (also known as myopericarditis) are inflammatory diseases involving the myocardium (with non-ischemic myocyte necrosis) and/or the pericardial sac. Myocarditis/pericarditis (MPC) may present with variable clinical signs, symptoms, etiologies and outcomes, including acute heart failure, sudden death, and chronic dilated cardiomyopathy. Possible undiagnosed and/or subclinical acute myocarditis, with undefined potential for delayed manifestations, presents further challenges for diagnosing an acute disease and may go undetected in the setting of infection as well as adverse drug/vaccine reactions.The most common causes of MPC are viral, with non-infectious, drug/vaccine associated hypersensitivity and/or autoimmune causes being less well defined and with potentially different inflammatory mechanisms and treatment responses. Potential cardiac adverse events following immunization (AEFIs) encompass a larger scope of diagnoses such as triggering or exacerbating ischemic cardiac events, cardiomyopathy with potential heart failure, arrhythmias and sudden death. The current published experience does not support a potential causal association with vaccines based on epidemiologic evidence of relative risk increases compared with background unvaccinated incidence. The only evidence supporting a possible causal association of MPC with a vaccine comes from case reports.Hypersensitivity MPC as a drug/vaccine induced cardiac adverse event has long been a concern for post-licensure safety surveillance, as well as safety data submission for licensure. Other cardiac adverse events, such as dilated cardiomyopathy, were also defined in the CDC definitions for adverse events after smallpox vaccination in 2006. In addition, several groups have attempted to develop and improve the definition and adjudication of post-vaccination cardiovascular events. We developed the current case definitions for myocarditis and pericarditis as an AEFI building on experience and lessons learnt, as well as a comprehensive literature review. Considerations of other etiologies and causal relationships are outside the scope of this document.     

How Contraceptive Use Affects Birth Intervals: Results of a Literature Review

Short birth intervals can have adverse consequences for maternal and infant outcomes. Optimal birth spacing is often presumed to be achieved through the practice of family planning and use of contraceptives, yet most of the available research does not address explicitly the contribution of contraceptive-method use to birth spacing or maternal and infant survival. We conducted a systematic literature review to assess the body of evidence linking contraceptive use to birth-interval length. Fourteen studies published in English between 1980 and 2008 met our eligibility criteria for inclusion. The findings from these studies are mixed but suggest that the use of contraceptives is protective against short birth intervals. Although results are favorable, many of the studies and methodologies employed are dated. More current research is needed to determine the impact of contraceptive-method use on birth-interval length in order to inform the promotion of family planning for reducing maternal and infant morbidity and mortality through birth spacing.     

Effect of hospital volume on maternal outcomes in women with prior cesarean delivery undergoing trial of labor

The authors examined the association between hospital volume of vaginal birth after cesarean section (VBAC) and VBAC failure, uterine rupture, and maternal morbidity. This was a secondary analysis of data from a retrospective cohort study carried out from 1995 to 2000. Trained nurses extracted detailed information from the medical records of more than 25,000 women with a prior cesarean delivery from 17 community and tertiary-care hospitals in the northeastern United States. The study sample included 12,844 women with prior cesarean section who attempted vaginal delivery with a singleton birth. Annual hospital VBAC volume was divided into tertiles. Primary outcomes included VBAC failure, uterine rupture, and a composite measure of maternal morbidity. The authors used multivariable logistic regression to assess the association between hospital VBAC volume and adverse VBAC outcomes after controlling for confounders. The authors did not find evidence of an association between hospital VBAC volume and the likelihood of adverse outcomes in VBAC after adjustment for patient mix. Other risk factors consistent with prior research were identified, including induction of labor, >/=2 prior cesarean deliveries, preeclampsia, diabetes mellitus, and high birth weight. Prior vaginal delivery was protective against adverse VBAC outcomes. The risk of an adverse VBAC outcome in low-volume hospitals was comparable to that in high-volume hospitals.     

Birth spacing and childhood mortality

Recent evidence from developing countries indicates that there is a relationship between the length of the interval between consecutive births and the survival of the younger sibling. This relationship has long been observed in the developed world. A study conducted by the World Health Organization in 9 largely metropolitan locations in developing countries found a reverse J-shaped pattern, with mortality rates initially falling with increased intervals but showing an upturn for the longest intervals of 5-6 and 6 or more years. The birth interval-mortality link tended to be stronger for postneonatal rather than neonatal and child mortality. A World Fertility Survey (WFS) cross-national analysis found a longer birth interval substantially improved the survival chance of the youngest child in all 29 countries studied. This advantage persisted to 5 years of age. The ratio of the infant mortality rate of children born within an interval of less than 2 years to that of those born after an interval of 4 years ranged from 1.26 in Venezuela to 3.91 in Syria. A 2nd WFS study found that the birth interval-mortality link persisted when maternal education was controlled. More detailed analysis of data gathered for this study from Pakistan revealed that the association between birth interval and mortality of the younger sibling was unaffected by the early death of the older sibling. Although it has been hypothesized that competition between children for food and attention is the major causal mechanism in the birth interval-mortality link, this finding suggests that maternal depletion (giving rise to low birth weights and inadequate breast milk) plays a role. However, the additional finding that survivorship of order 5 and more births was unaffected by average spacing patterns once the length of the immediately preceding birth interval was controlled suggests that maternal depletion may not be cumulative. The data from Pakistan further show interval length to have the same effect on mortality of the older sibling, even when length of breastfeeding was controlled, suggesting that involuntary weaning because of the next pregnancy is the critical explanatory factor. This research points to the need for a renewed emphasis on contraception for spacing purposes.     

Exploring the association between short/long preceding birth intervals and child mortality: using reference birth interval children of the same mother as comparison

Background

This study used data from recent Demographic and Health Surveys (DHS) to examine the impact of short or long preceding birth intervals on neonatal and under-five mortality. In order to minimize the effect of selection issues, we examined child mortality outcomes of the same mother, comparing short or long interval births against births with what had previously been considered optimal intervals.

Methods

We analyzed 47 DHS datasets from low- and middle-income countries. For each dataset, we compared neonatal and under-five mortality of short preceding interval births (<18 months, <24 months) to reference interval births (24-<60 months) of a mother, using conditional logistic regression matching on the mother. We also conducted the same matched analysis for long (≥60 months, ≥72 months) preceding interval births. These associations were then meta-analyzed. We also stratified the analyses by mothers’ completed fertility (fertility at end of reproductive period) to assess whether maternal characteristics highly correlated with completed fertility modify the association between birth interval and child mortality.

Results

Children with shorter preceding intervals had increased odds of both neonatal (<24 months, OR: 1.61, 95% CI: 1.52-1.70) and under-five mortality (<24 months, OR: 1.48, 95% CI: 1.40-1.56). When the associations were stratified by the mothers’ completed fertility, the impact of short intervals was greatly reduced or eliminated for low fertility mothers. In contrast, mortality associations became stronger for children of high fertility mothers. However, when the births of high fertility mothers were limited to birth orders 2-4, the associations were comparable to those of low fertility mothers. Longer preceding birth intervals had lower odds of mortality than reference intervals (i.e. under-5 mortality for ≥60 months, OR 0.59, 95% CI: 0.52-0.67). This effect was also mediated by mothers’ completed fertility; there was a strong protective effect of longer birth intervals for the high fertility mothers but not for low fertility mothers.

Conclusions

These analyses reproduced findings reported in previous literature that shorter birth intervals are associated with higher child mortality. However the negative impact of short birth intervals may only occur in high parity births. Reproductive health interventions that seek to lengthen birth intervals may have larger impact by targeting women with high parity. This finding is consistent with the concept of maternal depletion as the underlying cause of increased adverse child outcomes associated with shorter birth intervals.

     

HIV与HBV单独感染及共感染对妊娠结局的影响

HIV和HBV有较高的流行率,威胁人类健康。越来越多的研究发现孕产妇HIV/HBV感染与不良妊娠之间存在联系,而且孕产妇HIV/HBV感染还会增加HIV、HBV母婴传播的风险。但目前有关这两种病毒共感染对不良妊娠结局和母婴传播的影响尚不清楚,有待进一步深入研究,为制定有效的预防措施提供科学依据,促进母婴健康。     

Health impacts of family planning

Among the many effects of family planning is the influence ithas on mortality and morbidity in women and children throughthe mechanism of changing the number and spacing of children.There is a complex set of relationships between mother's age,parity, birth spacing and infant and child mortality and morbidity.Much effort has been put into untangling this web in the hopeof identifying clear causal connections, but for the most parton the basis of inadequate data. Rather than attempt to establishthe relative importance of child spacing as a cause of decreasesin mortality, this paper takes as its starting point that thereis a connection, and presents some possible causal mechanismswhich explain how short birth intervals and child mortalitycould be related. In addition the most frequently cited hypotheses-maternaldepletion and sibling competition-a third is examined-birthcrowding which, it is suggested, influences the pattern of thetransmission of infectious diseases and, in turn, mortality. In the field of maternal mortality, the data which could beused to quantify the benefits of family planning are in evenshorter supply; however, the causal connections are rather moreeasily identified. The final section combines parity-specificdata on maternal mortality with evidence of changes in fertilitypatterns brought about by family planning to assess how successfulwe can hope to be in reducing through birth control the numberof women who die in childbirth.     

Preceding birth intervals and child survival: searching for pathways of influence.

The importance of the length of preceding birth intervals for the survival chances of young children has been established, but the debate concerning the causal biomedical or behavioral mechanisms continues. This article uses data from 17 Demographic and Health Surveys to investigate the effect of birth intervals on child mortality: Anthropometry of children, recent morbidity of children, and use of health services are examined in addition to child survival data for children born in the five years before the survey. Various methodological approaches are used to investigate the relative importance of the postulated mechanisms linking birth intervals and child survival. Short preceding birth intervals are associated with increased mortality risks in the neonatal period and at 1-6 months of age, and, to a much lesser extent, at 7-23 months of age. The effects of short birth intervals on nutritional status are rather moderate, and there is a weak relationship with lower attendance at prenatal care services. No consistent relationship exists between the length of birth intervals and other health status or health-service utilization variables. The results indicate that prenatal mechanisms are more important than postnatal factors, such as sibling competition, in explaining the causal nature of the birth interval effect.     

Vitamin D and adverse pregnancy outcomes: beyond bone health and growth

Concerns exist about adequacy of vitamin D in pregnant women relative to both maternal and fetal adverse health outcomes. Further contributing to these concerns is the prevalence of inadequate and deficient vitamin D status in pregnant women, which ranges from 5 to 84% globally. Although maternal vitamin D metabolism changes during pregnancy, the mechanisms underlying these changes and the role of vitamin D during development are not well understood. Observational evidence links low maternal vitamin D status with an increased risk of non-bone health outcome in the mother (pre-eclampsia, gestational diabetes, obstructed labour and infectious disease), the fetus (gestational duration) and the older offspring (developmental programming of type 1 diabetes, inflammatory and atopic disorders and schizophrenia); but the totality of the evidence is contradictory (except for maternal infectious disease and offspring inflammatory and atopic disorders), lacking causality and, thus, inconclusive. In addition, recent evidence links not only low but also high maternal vitamin D status with increased risk of small-for-gestational age and schizophrenia in the offspring. Rigorous and well-designed randomised clinical trials need to determine whether vitamin D has a causal role in non-bone health outcomes in pregnancy.     

The Associations between Inter-Pregnancy Interval and Maternal and Neonatal Outcomes in Brazil

Objectives Global estimates of maternal and perinatal mortality have remained unchanged over the past 20 years, and strategies are being sought to decrease the occurrence of maternal and perinatal death. The objective of this study was to evaluate the association between inter-pregnancy interval and the occurrence of adverse maternal and perinatal outcomes. Methods Design and Setting: Cross-sectional study of the obstetrical and perinatal records in an intra-hospital obstetrics database between 1986 and 2000 at a tertiary maternity hospital in Brazil. Participants: A total of 14,930 records of parous women who delivered singleton infants. Main outcome measures: Crude and adjusted odds ratio estimates of gestational outcome according to inter-pregnancy intervals. Results During the period of the study, 34.6% of records referred to women with an inter-pregnancy interval <18 months. After the adjustment performed for 11 confounding factors and assuming an inter-pregnancy interval of 18–23 months as reference, short intervals (<6 months) were observed to be associated with a greater risk of low birth weight (odds ratio: 1.74; 95% confidence interval: 1.18–2.55), and preterm birth (1.56; 1.01–2.46). On the other hand, long intervals were significantly associated with fewer C-sections (0.69; 0.56–0.82), and a greater risk of premature rupture of membranes (PROM) (1.57; 1.20–2.06) and low birth weight (1.46; 1.03–2.06). Conclusions Short inter-pregnancy intervals are associated with a higher risk of low birth weight and preterm birth, while long intervals are associated with a higher risk of PROM, low birth weight and a lower risk of C-section.     

The relationship of interpregnancy interval to infant birthweight and length of gestation among low-risk women, Georgia

To examine the association between interpregnancy interval and low birthweight (< 2500 g), preterm delivery (< 37 weeks' gestation), and inadequate fetal growth, we studied a population-based sample of 23 388 white and 4885 black women at low risk for adverse pregnancy outcomes who delivered their first and second infants in Georgia from 1980 to 1992. We used fetal death and livebirth certificates. The interpregnancy interval was the time from delivery to the woman's next conception. For each pregnancy outcome, we stratified by race and used logistic regression to assess the association between interpregnancy interval and outcome, while controlling for confounders. Intervals <6 months were observed for 3.7% of white women and 7.0% of black women and intervals 48 months were seen for 16.8% of white women and 24.8% of black women. Results from logistic regression showed that, for both races, interpregnancy interval was associated with low birth-weight and preterm delivery. Nearly all of the increased risk occurred in intervals < 6 months or 48 months. The magnitude of the increase in risk associated with these intervals ranged from modest to moderate and was similar for black and white women. Because short interpregnancy intervals are rare and are weak risk factors among low-risk women, efforts to lengthen interpregnancy intervals are unlikely to reduce substantially their rates of adverse pregnancy outcomes.     

甲状腺自身性免疫与辅助生殖

甲状腺自身抗体可能与流产风险增加有关,但是否存在因果关系及相关机制尚不明确。甲状腺自身性免疫（thyroid autoimmunity,TAI）对辅助生殖结局的影响尚存争议。现有研究表明使用左旋甲状腺素、糖皮质激素、免疫球蛋白等改善TAI女性辅助生殖结局的证据不足,有待进一步研究。未来研究应探索甲状腺自身抗体与不良妊娠之间的因果关系。在研究设计时应考虑到甲状腺自身抗体滴度、不同授精方式、进行新鲜胚胎移植及冻融胚胎移植等因素的影响。需进一步研究卵细胞质内单精子注射/冻融胚胎移植是否更有利于行辅助生殖治疗的TAI女性的妊娠结局。     

Effects of Maternal Nutritional Supplements and Dietary Interventions on Placental Complications: An Umbrella Review,Meta-Analysis and Evidence Map

The placenta is a vital, multi-functional organ that acts as an interface between maternal and fetal circulation during pregnancy. Nutritional deficiencies during pregnancy alter placental development and function, leading to adverse pregnancy outcomes, such as pre-eclampsia, infants with small for gestational age and low birthweight, preterm birth, stillbirths and maternal mortality. Maternal nutritional supplementation may help to mitigate the risks, but the evidence base is difficult to navigate. The primary purpose of this umbrella review is to map the evidence on the effects of maternal nutritional supplements and dietary interventions on pregnancy outcomes related to placental disorders and maternal mortality. A systematic search was performed on seven electronic databases, the PROSPERO register and references lists of identified papers. The results were screened in a three-stage process based on title, abstract and full-text by two independent reviewers. Randomized controlled trial meta-analyses on the efficacy of maternal nutritional supplements or dietary interventions were included. There were 91 meta-analyses included, covering 23 types of supplements and three types of dietary interventions. We found evidence that supports supplementary vitamin D and/or calcium, omega-3, multiple micronutrients, lipid-based nutrients, and balanced protein energy in reducing the risks of adverse maternal and fetal health outcomes. However, these findings are limited by poor quality of evidence. Nutrient combinations show promise and support a paradigm shift to maternal dietary balance, rather than single micronutrient deficiencies, to improve maternal and fetal health. The review is registered at PROSPERO (CRD42020160887).     

Adverse birth outcomes in United Republic of Tanzania--impact and prevention of maternal risk factors

OBJECTIVE: To determine risk factors for poor birth outcome and their population attributable fractions. METHODS: 1688 women who attended for antenatal care were recruited into a prospective study of the effectiveness of syphilis screening and treatment. All women were screened and treated for syphilis and other reproductive tract infections (RTIs) during pregnancy and followed to delivery to measure the incidence of stillbirth, intrauterine growth retardation (IUGR), low birth weight (LBW) and preterm live birth. FINDINGS: At delivery, 2.7% of 1536 women experienced a stillbirth, 12% of live births were preterm and 8% were LBW. Stillbirth was independently associated with a past history of stillbirth, short maternal stature and anaemia. LBW was associated with short maternal stature, ethnicity, occupation, gravidity and maternal malaria whereas preterm birth was associated with occupation, age of sexual debut, untreated bacterial vaginosis and maternal malaria. IUGR was associated with gravidity, maternal malaria, short stature, and delivering a female infant. In the women who had been screened and treated for syphilis, in between 20 and 34% of women with each outcome was estimated to be attributable to malaria, and 63% of stillbirths were estimated as being attributable to maternal anaemia. Screening and treatment of RTIs was effective and no association was seen between treated RTIs and adverse pregnancy outcomes. CONCLUSION: Maternal malaria and anaemia continue to be significant causes of adverse pregnancy outcome in sub-Saharan Africa. Providing reproductive health services that include treatment of RTIs and prevention of malaria and maternal anaemia to reduce adverse birth outcomes remains a priority.     

Ambient air pollution and pregnancy outcomes: a review of the literature

Over the last decade or so, a large number of studies have investigated the possible adverse effects of ambient air pollution on birth outcomes. We reviewed these studies, which were identified by a systematic search of the main scientific databases. Virtually all reviewed studies were population based, with information on exposure to air pollution derived from routine monitoring sources. Overall, there is evidence implicating air pollution in adverse effects on different birth outcomes, but the strength of the evidence differs between outcomes. The evidence is sufficient to infer a causal relationship between particulate air pollution and respiratory deaths in the postneonatal period. For air pollution and birth weight the evidence suggests causality, but further studies are needed to confirm an effect and its size and to clarify the most vulnerable period of pregnancy and the role of different pollutants. For preterm births and intrauterine growth retardation (IUGR) the evidence as yet is insufficient to infer causality, but the available evidence justifies further studies. Molecular epidemiologic studies suggest possible biologic mechanisms for the effect on birth weight, premature birth, and IUGR and support the view that the relation between pollution and these birth outcomes is genuine. For birth defects, the evidence base so far is insufficient to draw conclusions. In terms of exposure to specific pollutants, particulates seem the most important for infant deaths, and the effect on IUGR seems linked to polycyclic aromatic hydrocarbons, but the existing evidence does not allow precise identification of the different pollutants or the timing of exposure that can result in adverse pregnancy outcomes.     

Pregnancy characteristics and outcomes of Cambodian refugees.

This study describes the perinatal characteristics of Cambodian refugees in Massachusetts. Data were abstracted from the records of 452 consecutive pregnancies among Cambodian women and 110 low-income Whites receiving obstetrical services at the same clinic and hospital in Lowell, Massachusetts. Pregnancies of Cambodian women were marked by a higher proportion of older mothers, grand multiparas, previous adverse birth outcomes, and short interpregnancy intervals. We identified maternal anemia (29.9 percent with hemoglobin less than 110 g/L) and inadequate utilization of prenatal care (32.3 percent with first visit in the 3rd trimester) as possible risk factors for the Cambodians. The prevalence of primary cesarean birth was only 6.3 percent in the Cambodians, compared to 15.6 percent in the comparison group, largely due to the infrequent occurrence of prolonged labor among multiparas. Despite the prominence of several risk factors for adverse birth outcomes in this population, major pregnancy complications were less common and the prevalence of low birthweight (6.4 percent) was close to the state average. Logistic regression analysis of risk factors for low birthweight identified young maternal age and short stature as the strongest factors operative in this community. Many of our findings are consistent with a strong cultural emphasis on managing the size of the baby to avoid a difficult labor and delivery.     

Thyroid-Disrupting Chemicals: Interpreting Upstream Biomarkers of Adverse Outcomes

Background

There is increasing evidence in humans and in experimental animals for a relationship between exposure to specific environmental chemicals and perturbations in levels of critically important thyroid hormones (THs). Identification and proper interpretation of these relationships are required for accurate assessment of risk to public health.

Objectives

We review the role of TH in nervous system development and specific outcomes in adults, the impact of xenobiotics on thyroid signaling, the relationship between adverse outcomes of thyroid disruption and upstream causal biomarkers, and the societal implications of perturbations in thyroid signaling by xenobiotic chemicals.

Data sources

We drew on an extensive body of epidemiologic, toxicologic, and mechanistic studies.

Data synthesis

THs are critical for normal nervous system development, and decreased maternal TH levels are associated with adverse neuropsychological development in children. In adult humans, increased thyroid-stimulating hormone is associated with increased blood pressure and poorer blood lipid profiles, both risk factors for cardiovascular disease and death. These effects of thyroid suppression are observed even within the “normal” range for the population. Environmental chemicals may affect thyroid homeostasis by a number of mechanisms, and multiple chemicals have been identified that interfere with thyroid function by each of the identified mechanisms.

Conclusions

Individuals are potentially vulnerable to adverse effects as a consequence of exposure to thyroid-disrupting chemicals. Any degree of thyroid disruption that affects TH levels on a population basis should be considered a biomarker of adverse outcomes, which may have important societal outcomes.     

Residential proximity to heavy traffic and birth weight in Shizuoka, Japan

An association between exposure to traffic-related air pollution and reduced birth weight has been suggested. However, previous studies have failed to adjust for maternal size, which is an indicator of individual genetic growth potential. Therefore, we evaluated the association of air pollution with birth weight, term low birth weight (term-LBW), and small for gestational age (SGA), with adjustment for maternal size. Individual data were extracted from a database that is maintained by a maternal and perinatal care center in Shizuoka, Japan. We identified liveborn singleton births (n=14,204). Using geocoded residential information, each birth was assigned a number of traffic-based exposure indicators: distance to a major road; distance-weighted traffic density; and estimated concentration of nitrogen dioxide by land use regression. The multivariate adjusted odds ratios and their 95% confidence intervals (CIs) for the associations between exposure indicators and outcomes were then estimated using logistic regression models. Overall, exposure indicators of air pollution showed no clear pattern of association. Although there are many limitations, we did not find clear associations between birth-weight-related outcomes and the three markers of traffic-related air pollution.     

Report of the WHO technical consultation on the effect of maternal influenza and influenza vaccination on the developing fetus: Montreal,Canada, September 30–October 1, 2015

In 2012, the World Health Organization (WHO) released a position paper on influenza vaccination recommending that pregnant women have the highest priority for seasonal vaccination in countries where the initiation or expansion of influenza immunization programs is under consideration. Although the primary goal of the WHO recommendation is to prevent influenza illness in pregnant women, the potential benefits of maternal immunization in protecting young infants are also recognized. The extent to which maternal influenza vaccination may prevent adverse birth outcomes such as preterm birth or small-for-gestational-age birth, however, is unclear as available studies are in disagreement.To inform WHO about the empirical evidence relating to possible benefits of influenza vaccination on birth outcomes, a consultation of experts was held in Montreal, Canada, September 30–October 1, 2015. Presentations and discussions covered a broad range of issues, including influenza virus infection during pregnancy and its effect on the health of the mother and the fetus, possible biological mechanisms for adverse birth outcomes following maternal influenza illness, evidence on birth outcomes following influenza illness during pregnancy, evidence from both observational studies and randomized controlled trials on birth outcomes following influenza vaccination of pregnant women, and methodological issues. This report provides an overview of the presentations, discussions and conclusions.