Estimating the impact of maternal anemia on low-birth-weight in Sub-Saharan African countries: propensity score matching analysis – BMC Pregnancy and Childbirth

Report on the Causal Effect of Maternal Anemia on Low Birth Weight in Sub-Saharan Africa: A Propensity Score Matching Analysis

Introduction: Low Birth Weight as an Obstacle to Sustainable Development Goals

Low Birth Weight (LBW), defined by the World Health Organization (WHO) as a birth weight under 2500g, is a critical indicator of intrauterine health and a significant determinant of neonatal survival and long-term well-being. The prevalence of LBW presents a formidable challenge to the achievement of the United Nations Sustainable Development Goals (SDGs), particularly those concerning global health and nutrition.

• SDG 3 (Good Health and Well-being): LBW is a primary contributor to neonatal mortality, directly impeding progress towards Target 3.2, which aims to end preventable deaths of newborns and children under five.
• SDG 2 (Zero Hunger): LBW is an intergenerational manifestation of malnutrition, undermining Target 2.2, which seeks to end all forms of malnutrition.

This report analyzes the causal relationship between maternal anemia and LBW in Sub-Saharan Africa, utilizing a robust methodological approach to inform targeted interventions aligned with the SDG framework.

The Impact of Low Birth Weight on Health and Development Outcomes

Immediate and Long-Term Health Consequences

The implications of LBW extend from infancy through adulthood, creating a cycle of poor health that hinders progress towards SDG 3.

1. Neonatal Morbidity and Mortality: LBW is responsible for 60% to 80% of all newborn deaths worldwide. Infants with LBW have a risk of mortality approximately 20 times higher than infants of normal birth weight, representing a major failure in achieving SDG Target 3.2.
2. Childhood Development: Survivors of LBW often face significant health challenges that compromise their quality of life and educational attainment, including:
   • Impaired cognitive skills and neurological abnormalities.
   • Increased susceptibility to infections.
3. Adult Non-Communicable Diseases (NCDs): LBW is a known risk factor for the later development of NCDs such as diabetes, hypertension, and coronary heart disease. Addressing LBW is therefore crucial for meeting SDG Target 3.4, which aims to reduce premature mortality from NCDs.

Global Disparities and the Challenge in Developing Nations

The burden of LBW is disproportionately borne by low- and middle-income countries (LMICs), where the prevalence (16.5%) is more than double that of high-income nations (7%). Annually, approximately 20 million infants are born with LBW, the vast majority in developing regions, highlighting a critical inequality that must be addressed to achieve the SDGs.

Maternal Anemia: A Primary Driver of Low Birth Weight

The Link Between Malnutrition and Neonatal Health

Maternal anemia, a condition characterized by a hemoglobin concentration below 11 g/dl, is a widespread nutritional deficiency that directly undermines both SDG 2 (Zero Hunger) and SDG 3 (Good Health and Well-being). It is a strong predictor of adverse pregnancy outcomes, including LBW.

• Prevalence: An estimated 38.2% of pregnant women globally are anemic, with the highest burdens in Africa (46.3%) and Southeast Asia (48.7%). In Sub-Saharan Africa alone, 17.2 million pregnant women are affected.
• Physiological Impact: Maternal anemia leads to reduced oxygen-carrying capacity in the blood. This creates a state of chronic hypoxia for the fetus, which impairs placental development and function, thereby restricting nutrient and oxygen transport and leading to poor intrauterine growth and LBW.
• Root Causes: The drivers of anemia are multifaceted and linked to systemic failures in health and nutrition, including poor dietary intake, inadequate iron and folic acid supplementation, and insufficient antenatal care.

Methodological Approach

Study Design and Data Source

This analysis utilized secondary data from the most recent Demographic and Health Surveys (DHS) conducted between 2012 and 2023 across 27 Sub-Saharan African countries. A weighted sample of 54,904 women was included in this cross-sectional study.

Variable Definitions

1. Outcome Variable: Low Birth Weight (LBW), defined as a recorded birth weight of less than 2500g.
2. Treatment Variable: Maternal Anemia, defined as a hemoglobin level below 11 g/dL, adjusted for altitude.
3. Confounding Variables: Factors known to influence both anemia and LBW were included to ensure a robust analysis. These comprised maternal age, education, household wealth, marital status, employment, media exposure, number of antenatal care visits, and iron supplementation during pregnancy.

Statistical Analysis: Propensity Score Matching (PSM)

To isolate the causal effect of anemia on LBW from confounding factors, a Propensity Score Matching (PSM) technique was employed. This statistical method simulates a randomized control trial by creating two comparable groups: anemic (treated) and non-anemic (control) mothers who share a similar probability (propensity score) of being anemic based on observed characteristics. This ensures that any observed difference in LBW rates can be more confidently attributed to the mother’s anemic status.

• The Average Treatment Effect on the Treated (ATT) was calculated to estimate the impact of anemia on the incidence of LBW.
• The quality of the matching was assessed by confirming that covariates were balanced between the groups post-matching.
• A sensitivity analysis was conducted to test the robustness of the findings against potential unobserved biases.

This rigorous approach addresses the limitations of previous observational studies and provides stronger evidence for policymakers working to achieve SDG 2 and SDG 3 in Sub-Saharan Africa.

Analysis of Sustainable Development Goals in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

• SDG 2: Zero Hunger

  The article directly connects to SDG 2 by focusing on maternal anemia, which it explicitly identifies as a “nutritional condition.” It highlights causes such as “low dietary consumption” and “poor diet quality,” which are central to the goal of ending all forms of malnutrition.

• SDG 3: Good Health and Well-being

  This is the primary SDG addressed. The article’s core subject is low birth weight (LBW) and its severe consequences for newborn health and survival. It explicitly states that “60 to 80% of newborn deaths are caused by low birth weight” and that LBW is linked to long-term health problems like “excessive blood pressure, diabetes, and coronary heart disease later in life.” The focus on maternal health (anemia in pregnancy) and child mortality makes this a central theme.

• SDG 10: Reduced Inequalities

  The article highlights significant disparities in health outcomes between different parts of the world. It points out that the burden of LBW and maternal anemia is disproportionately high in developing regions. For instance, it states, “the prevalence [of LBW] in low- and middle-income countries (LMICs) is twice as high (16.5%)” compared to high-income countries (7%). It also notes the high burden of anemia in “Southeast Asia (48.7%) and in Africa (46.3%),” directly addressing the goal of reducing inequalities between countries.

2. What specific targets under those SDGs can be identified based on the article’s content?

1. Target 2.2: End all forms of malnutrition

   This target aims to “end all forms of malnutrition… and address the nutritional needs of… pregnant and lactating women.” The article’s detailed discussion of anemia as a widespread nutritional deficiency among pregnant women (“An estimated 32.4 million pregnant women worldwide (38.2%) were anemic”) and its link to poor dietary intake directly aligns with this target.

2. Target 3.2: End preventable deaths of newborns and children under 5

   This target aims to “reduce neonatal mortality to at least as low as 12 per 1,000 live births.” The article provides a strong rationale for focusing on LBW to achieve this target by stating that “low birth weight babies have a roughly 20 times higher chance of dying” and are responsible for “60 to 80% of newborn deaths.” Addressing LBW is presented as a critical step in preventing newborn deaths.

3. Target 3.4: Reduce premature mortality from non-communicable diseases (NCDs)

   This target focuses on reducing mortality from NCDs through prevention. The article connects the issue of LBW to this target by explaining its long-term consequences. It notes that LBW “is linked to excessive blood pressure, diabetes, and coronary heart disease later in life,” positioning the prevention of LBW as a long-term strategy for preventing future NCDs.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

• Prevalence of low birth weight (LBW)

  This is the primary indicator discussed and is the main outcome variable of the study. The article defines it (“birth weight less than 2500 g”) and provides prevalence data for different regions (“the prevalence in low- and middle-income countries (LMICs) is twice as high (16.5%)”). This indicator is crucial for tracking progress on Target 3.2.

• Prevalence of anemia in pregnant women

  The article uses this as a key indicator for maternal malnutrition (Target 2.2). It provides a clear definition (“hemoglobin concentration of less than 11 g/dl”) and detailed statistics on its prevalence globally (“38.2%”), regionally (“Africa (46.3%)”), and within specific populations (“pregnant women”).

• Newborn mortality rate

  While the article does not provide a specific rate, it strongly implies this indicator by repeatedly linking LBW directly to newborn deaths (“60 to 80% of newborn deaths are caused by low birth weight”). The prevalence of LBW is used as a proxy to understand the scale of the challenge in reducing newborn mortality (Target 3.2).

• Comparative prevalence rates between regions/countries

  To measure progress on SDG 10, the article provides comparative data that serves as an indicator of inequality. The statistics comparing LBW prevalence in “low- and middle-income countries” versus “high-income countries” directly measure the health gap that needs to be closed.

4. Table of SDGs, Targets, and Indicators

Source: bmcpregnancychildbirth.biomedcentral.com