Iron-deficiency anemia is the most common form of anemia during pregnancy. Iron deficiency is the most prevalent disease among women of reproductive age globally, and it is even more common during pregnancy due to the increased iron requirements. This article discusses the causes and risks of iron deficiency during pregnancy, screening and diagnosis of iron deficiency anemia.

Definition and Incidence

The World Health Organization recommends the following hemoglobin (Hb) concentrations during pregnancy:

• First trimester (0-12 weeks): Hb ≥ 11 g/dL
• Second trimester (13-26 weeks): Hb ≥ 10.5 g/dL
• Third trimester (27 weeks and beyond): Hb ≥ 11 g/dL

If the hemoglobin level is lower than these standards, it may suggest anemia, particularly iron-deficiency anemia, and further assessment and iron supplementation should be considered. Anemia during pregnancy is a global health and public health issue.

The global prevalence of anemia among pregnant women is 41.8%, with 57.1% of pregnant women in Africa affected, 48.2% in Southeast Asia, and 24%-25% in the Americas and Europe. In China, the prevalence of anemia in pregnant women ranges from 42% to 73%, with urban prevalence at 34% and rural prevalence at 46%. The prevalence of anemia during the early, middle, and late stages of pregnancy is 36%, 52%, and 60%, respectively.

Causes and Iron Requirements During Pregnancy

Pregnancy-related iron-deficiency anemia is common due to physiological and pathological changes, primarily related to increased iron demand and relative or absolute insufficiency of iron supply.

During pregnancy, the ferritin test is an effective tool for monitoring the stability of ferritin levels in the blood. The procedure is straightforward, and results are available quickly. This test offers the convenience of obtaining rapid ferritin results at home, making it ideal for pregnant women who may be unable to leave their homes, and can assist in the early detection of potential iron deficiencies.

1. Increased Iron Demand

During a normal pregnancy, the total iron requirement is about 1240 mg, with 500-600 mg required for increased red blood cell volume, and approximately 300 mg required for the fetus and placenta. The daily iron requirement for pregnant women is about 4.4 mg (rising from 0.8 mg/d in early pregnancy to 7.5 mg/d in late pregnancy), and the average iron absorption rate is around 10%, meaning a dietary iron intake of 40 mg/d is necessary.

2. Insufficient Iron Intake

Iron intake may be affected by early pregnancy vomiting or dietary preferences.

3. Iron Absorption Disorders

Malnutrition or dietary preferences often lead to insufficient protein intake, which affects iron absorption. Gastrointestinal disorders such as low stomach acid, gastric mucosal atrophy, or chronic diarrhea can also hinder iron absorption.

4. Increased Iron Loss

Pregnancy-related bleeding disorders, such as placenta previa, and chronic diseases including infections and chronic liver or kidney diseases, can also lead to anemia.

5. Insufficient Iron Storage

Anemia before pregnancy may persist or worsen during pregnancy. Around 40% of women have low iron stores or iron deficiency before pregnancy (serum ferritin).

Risks of Anemia

Maternal Risks

During pregnancy, a series of physiological changes occur in the maternal circulatory system, including blood dilution, which exacerbates anemia and increases the burden on the heart. Anemia reduces the blood's oxygen-carrying capacity, and while mild anemia may have minimal impact on pregnancy, severe anemia can lead to serious consequences.

Due to insufficient oxygen reserves, women with anemia have a lower tolerance to blood loss, which increases the need for transfusions and the risk of transfusion-related complications. Even if blood loss during labor or postpartum is minimal, it can lead to shock or even death. According to WHO data, maternal mortality related to anemia worldwide is 40%.

Fetal Risks

During anemia, reduced oxygen supply to the placenta can result in fetal growth restriction, fetal distress, miscarriage, preterm birth, stillbirth, neonatal asphyxia, and hypoxic-ischemic encephalopathy. The incidence of miscarriage and preterm birth increases with the severity of anemia.

Neonatal Risks

The morbidity and mortality rates for newborns of anemic mothers are higher. When maternal iron stores are depleted, fetal iron stores are reduced, leading to anemia or iron deficiency during the first year of life. Iron-deficient children may exhibit behavioral abnormalities and low Bayley mental developmental indices. Iron supplementation can improve maternal iron stores and increase neonatal iron stores, which helps prevent iron deficiency during the first year and reduces neonatal mortality. Preventing iron deficiency during pregnancy also has some effect in reducing the risk of hypertension in offspring during adulthood.

In fetuses and infants, iron is primarily used for red blood cell production. If iron supply cannot meet this demand, it may lead to iron deficiency in other tissues, including skeletal muscle, the heart, and the brain. Infants and children born to iron-deficient mothers tend to have slower brain cognitive development and lower IQ compared to those born to iron-sufficient mothers.

Screening and Diagnosis

Screening

All pregnant women should be screened for anemia during their first prenatal checkup and again at 28 weeks of pregnancy. Hb measurement is the initial screening test for anemia, and serum ferritin testing may be done if conditions allow.

Even before Hb levels drop, pregnant women may already be iron-deficient, so it is recommended to test serum ferritin if possible. Based on serum ferritin levels, decisions can be made regarding whether and how to supplement iron. For those unable to test serum ferritin, iron supplementation should be guided by local epidemiological data on anemia prevalence among pregnant women in the region.

For pregnant women who find it inconvenient to visit healthcare facilities regularly, using a home hemoglobin meter can be an effective solution. This device allows for continuous monitoring of hemoglobin levels, enabling women to promptly assess their blood's hemoglobin content and quickly identify any potential signs of anemia.

Diagnosis

Pregnancy-related anemia is diagnosed when Hb is below 110 g/L. Anemia is classified as:

• Mild anemia: Hb 100-109 g/L
• Moderate anemia: Hb 70-99 g/L
• Severe anemia: Hb < 70 g/L

If Hb levels are below the physiological lower limit during pregnancy, iron-deficiency anemia should be considered first. Laboratory tests should be used to diagnose anemia and iron deficiency. Laboratory tests for pregnancy-related iron-deficiency anemia include:

Complete Blood Count (CBC): CBC is the primary test for diagnosing anemia and includes Hb concentration, hematocrit, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), red blood cell count, and reticulocyte count. In most cases, these parameters will show significant changes in persistent and severe iron deficiency. Many women with iron deficiency may still have Hb levels within the normal range, so more sensitive tests are needed for early detection.

Serum Ferritin: Serum ferritin measurement is the gold standard for diagnosing iron-deficiency anemia in laboratory tests. Regardless of Hb levels, serum ferritin typically reflects the body's iron stores. Low serum ferritin levels usually indicate insufficient iron reserves, which is an early sign of iron-deficiency anemia.

Serum Iron, Soluble Transferrin Receptor, and Transferrin Saturation: Serum iron is influenced by many factors and is not a reliable indicator of iron storage. The soluble transferrin receptor increases with iron deficiency or increased cellular iron demand and is unaffected by infections. Transferrin saturation is influenced by factors such as diurnal variations and nutrition, making it unreliable for diagnosing iron storage status. A normal serum ferritin level with reduced transferrin saturation may indicate underlying iron deficiency, particularly in early-stage iron deficiency. Therefore, combining multiple diagnostic indicators, especially soluble transferrin receptor and ferritin levels, is crucial for accurately diagnosing iron deficiency and evaluating iron metabolism.