The U.S. Preventive Services Task Force has concluded there is insufficient evidence to assess the balance of benefits and harms of screening for iron deficiency and iron deficiency anemia in pregnant persons, as well as routine iron supplementation during pregnancy.

In its updated recommendation statement, the U.S. Preventive Services Task Force (USPSTF) issued two "I" statements, indicating inadequate evidence to recommend for or against these preventive services in asymptomatic pregnant adolescents and adults. This recommendation is consistent with the USPSTF's 2015 statement.

The USPSTF commissioned a systematic review evaluating evidence on screening and supplementation for iron deficiency with and without anemia during pregnancy. The review included randomized clinical trials, controlled observational studies, and large uncontrolled observational studies on harms.

Key Findings

Key findings from the evidence review include:

• The estimated prevalence of iron deficiency during pregnancy is 18%, increasing from 6.9% in the first trimester to 28.4% in the third trimester.
• Approximately 5% of pregnant persons have iron deficiency anemia.
• Iron deficiency anemia prevalence varies by race and ethnicity, with higher rates among Black and Mexican-American pregnant persons.

This recommendation applied to asymptomatic pregnant adolescents and adults, excluding those who were severely malnourished, had symptoms of iron deficiency or iron deficiency anemia, or had specific hematologic conditions or nutritional deficiencies that may increase their need for iron.

Screening Evidence

• No studies directly examined the benefits of screening and treating screen-detected iron deficiency or iron deficiency anemia on maternal and infant health outcomes.
• One observational study showed an association between successful treatment of anemia and reduced odds of preeclampsia (adjusted odds ratio [OR] = 0.75, 95% confidence interval [CI] = 0.61–0.91) and preterm birth (adjusted OR = 0.59, 95% CI = 0.47–0.72) compared to persons without anemia.
• There is limited evidence on risk prediction tools for identifying pregnant persons at increased risk for iron deficiency or iron deficiency anemia.

Supplementation Evidence

The review identified 16 studies comparing routine iron supplementation to no supplementation during pregnancy. Key findings include:

• No differences in maternal quality of life (one trial, n = 430)
• No significant differences in rates of hypertensive disorders of pregnancy (five trials, n = 13,610; relative risk [RR] = 1.24, 95% CI = 0.75-2.06; I² = 48.0%)
• No significant differences in cesarean delivery rates (eight trials, n = 4,919; RR, 1.01, 95% CI = 0.90-1.14; I² = 42.7%)
• No association between supplementation and infant mortality (five trials)
• No significant differences in risk of preterm birth (five trials, n = 16,827; RR = 0.92, 95% CI = 0.81-1.04; I² = 0.0%)
• No significant differences in low–birth weight infants (six trials, n = 15,591; RR = 0.95, 95% CI = 0.79-1.14; I² = 0.0%)
• Inconsistent and imprecise evidence on small for gestational age infants (four trials, n = 5,386; RR = 0.94, 95% CI = 0.67-1.31; I² = 75.5%).

Iron supplementation was associated with improved maternal hematologic indices across 16 trials:

• Decreased risk of maternal iron deficiency anemia during the third trimester (three trials; n = 330; RR = 0.63, 95% CI = 0.41-0.97; I² = 0%; absolute risk difference [ARD = −4%, 95% CI = −8% to 0%)
• Decreased risk of maternal iron deficiency anemia at term (four trials; n = 2,230; RR = 0.40, 95% CI = 0.26–0.61; I² = 20.5%; ARD = −10%, 95% CI = −16% to −3%)
• Decreased risk of maternal iron deficiency during the third trimester (four trials; n = 1,220; RR = 0.70, 95% CI = 0.53–0.92; I² = 77.4%; ARD = −17%, 95% CI = −24% to −10%)
• Decreased risk of maternal iron deficiency at term (six trials; n = 2,361; RR = 0.47, 95% CI = 0.33–0.67; I² = 81.9%; ARD = −34%, 95% CI = −46% to −22%)
• Decreased risk of maternal anemia during the third trimester (seven trials; n = 2,148; RR = 0.71, 95% CI = 0.51-0.97; I² = 64.2%; ARD = −7.97%, 95% CI = −15.28% to −0.66%)
• Decreased risk of maternal anemia at term (four trials; n = 2,261; RR = 0.43, 95% CI = 0.26-0.72; I² = 43.7%; ARD = −11.73%, 95% CI = −14.87% to −8.60%).

Harms of Supplementation

Twelve trials (n = 22,716) reported on harms of routine supplementation during pregnancy. Most trials reported transient gastrointestinal effects, such as nausea, constipation, and diarrhea. One trial (n = 12,513) found iron supplementation starting in the second trimester was associated with increased risk of gastrointestinal symptoms vs placebo (3.6% vs 2.3%; RR = 1.59, 95% CI = 1.28–1.97).

Future Research Needs

The USPSTF identified several research gaps, including:

• Studies assessing whether changes in maternal iron status improve maternal and infant health outcomes in settings relevant to U.S. primary care.
• Research on the benefits and harms of screening for iron deficiency and iron deficiency anemia during pregnancy on maternal and infant health outcomes.
• Studies evaluating the benefits and harms of treatment in asymptomatic, screen-detected populations with iron deficiency and iron deficiency anemia during pregnancy.
• Research on the benefits and harms of routine iron supplementation in asymptomatic pregnant persons without known iron deficiency or iron deficiency anemia.

The USPSTF recommendation highlights the need for more high-quality research to determine the balance of benefits and harms of screening and supplementation for iron deficiency and iron deficiency anemia during pregnancy in settings relevant to U.S. primary care clinical practice.

Conflict of interest disclosures could be found in the recommendation statement.