Can infections in pregnancy lead to CHD? 

Clinical research confirms that certain maternal infections and high fevers during the first trimester significantly increase the risk of congenital heart disease (CHD). Pathogens can disrupt fetal heart development, leading to structural defects. Early detection through NHS screening remains the primary way to monitor these risks and ensure the safety of both mother and baby. 

Congenital Heart Disease (CHD) is a term used to describe a range of birth defects that affect the normal way the heart works. While many heart defects are identified during routine prenatal scans, understanding the underlying causes is a priority for expectant parents and medical professionals alike. Maternal health during the early stages of gestation is a critical factor in the development of the fetal cardiovascular system. This article examines the relationship between infections during pregnancy and the development of heart defects, providing a clear overview of the risks, causes, and preventive measures supported by UK clinical standards. 

What We’ll Discuss in This Article 

• The biological connection between maternal illness and fetal heart formation. 

• Specific viral and bacterial pathogens associated with cardiac defects. 

• The impact of maternal hyperthermia (fever) on the developing fetus. 

• How clinical teams differentiate between genetic and environmental heart defects. 

• The critical timeline for organogenesis during the first trimester. 

• Practical steps for infection prevention and monitoring in the UK. 

Maternal Infections and the Risk of CHD 

Maternal infections during the first trimester can cause congenital heart disease (CHD) by disrupting fetal organogenesis. Research indicates that viral pathogens and high maternal fever interfere with the heart’s structural development, potentially leading to defects like septal holes or valve issues. Early detection through NHS screening remains the primary way to monitor these risks and manage outcomes. 

The development of the human heart is a complex process that occurs very early in pregnancy, often before a woman even knows she is pregnant. Between the third and eighth weeks of gestation, the heart moves from a simple tube structure to a complex organ with four chambers and major blood vessels. If a pathogen, such as a virus, crosses the placental barrier during this time, it can interfere with the delicate cellular signalling required for this transformation. 

The presence of an infection can led to inflammation or direct cellular damage. For instance, some viruses can infect the cells that are destined to become the heart muscle or the valves, leading to ‘structural anomalies’. Clinical data suggests that while the overall risk remains statistically low for the general population, the presence of specific infections significantly shifts the probability of a cardiac defect occurring. 

How Fever Influences Heart Development 

Maternal fever (hyperthermia) is a known trigger for heart defects. When the mother’s core temperature rises above 38°C in early pregnancy, it can disrupt the protein folding and cell migration required for the fetal heart’s plumbing. This physiological response to infection is often as significant a risk factor as the underlying virus or bacteria itself, requiring prompt management. 

Fever is the body’s natural response to infection, but in the context of pregnancy, it serves as a ‘teratogen’ a substance or condition that can interfere with fetal development. High temperatures can cause ‘heat-shock’ responses in fetal cells. These responses can lead to cell death or altered migration of neural crest cells, which are essential for forming the ‘outflow tracts’ of the heart (the aorta and pulmonary artery). 

Research has shown that prolonged or high-grade fevers are specifically linked to conotruncal defects, such as Tetralogy of Fallot. Clinical guidance emphasizes the importance of controlling fevers with pregnancy-safe medications, like paracetamol, as soon as they arise to mitigate these developmental risks. 

Causes: Viral and Bacterial Pathogens 

Several pathogens are clinically linked to CHD, including Rubella, Cytomegalovirus (CMV), and Coxsackievirus B. These agents can cross the placenta and directly damage developing cardiac tissues or cause inflammatory responses that alter structural growth. Maintaining up to date vaccinations is the most effective way to prevent these infection-based causes of heart defects. 

The table below outlines the primary pathogens associated with increased cardiac risk during pregnancy: 

Pathogen Type	Specific Infection	Associated Cardiac Defect	Clinical Risk Level
Viral	Rubella (German Measles)	PDA and Pulmonary Stenosis	High (if unvaccinated)
Viral	Cytomegalovirus (CMV)	Septal Defects (holes in the heart)	Moderate
Viral	Coxsackievirus B	Myocarditis and Valve issues	Variable
Viral	Influenza (with high fever)	Right Ventricular Obstruction	Moderate
Bacterial	Chlamydia psittaci	General structural abnormalities	Low/Emerging

In the UK, the success of the MMR (Measles, Mumps, and Rubella) vaccination program has made Rubella-related CHD rare. However, other viruses like CMV remain a concern because there is currently no vaccine available. CMV is often spread through contact with the saliva or urine of young children, making hygiene a vital part of prenatal care. 

Triggers: Environmental and Physiological Factors 

Environmental triggers such as high maternal body temperature and specific viral exposures during weeks three to eight of pregnancy are the most critical. During this window, the fetal heart is highly sensitive to external disruptions. Factors like untreated influenza or secondary bacterial infections can trigger inflammatory pathways that interfere with normal valve and vessel formation. 

Timing is the most significant ‘trigger’ in the relationship between infection and CHD. An infection that occurs in the second or third trimester is far less likely to cause a structural heart defect because the heart’s anatomy is already established. Instead, late-pregnancy infections might lead to other complications, such as premature birth or fetal growth restriction. 

Physiological stress on the mother’s body during a severe illness can also reduce the oxygen supply to the placenta. This ‘hypoxia’ can trigger compensatory mechanisms in the fetus that may affect the development of the heart’s muscular walls. 

Differentiation: Infection-Induced vs. Genetic Defects 

It is vital to distinguish between infection induced CHD and genetic heart defects. While genetic defects are caused by chromosomal abnormalities or inherited traits, infection induced CHD occurs in a genetically typical fetus due to external environmental factors. Understanding this difference helps clinical teams determine the likelihood of recurrence in future pregnancies. 

When a baby is diagnosed with a heart defect, clinical teams often perform genetic testing to see if there is an underlying chromosomal cause, such as Down’s Syndrome or DiGeorge Syndrome. If no genetic link is found, the focus shifts to environmental factors, including the mother’s health history during the first trimester. 

• Genetic CHD: Often involves multiple organ systems and has a higher risk of recurring in future pregnancies. 

• Infection-Induced CHD: Usually limited to the structural heart defect itself and does not carry a higher risk for future pregnancies once the mother is no longer infected or is vaccinated. 

To Summarise 

Maternal infections and high fevers during the first trimester are established but manageable risk factors for congenital heart disease. While the biological mechanisms involve complex disruptions to cell migration and protein folding, the clinical approach focuses on prevention through vaccination and the prompt treatment of fevers. Most expectant mothers who experience minor illnesses go on to have healthy babies, but awareness of these risks ensures that healthcare providers can offer appropriate screening and support. 

If you experience severe, sudden, or worsening symptoms, such as a very high fever that does not respond to paracetamol, a widespread rash, or difficulty breathing, call 999 immediately. 

You may find our free Pregnancy Due Date Calculator helpful for understanding your current stage of gestation and developmental milestones. 

Authority Snapshot (E-E-A-T Block) 

This article was reviewed by Dr. Stefan Petrov, a UK-trained physician with an MBBS and extensive experience in general medicine, surgery, and emergency care. Dr. Petrov has contributed to medical education and clinical skill training, ensuring that the health information provided is accurate and follows current NHS and NICE guidelines. This article provides a safe, evidence-based overview of how maternal infections interact with fetal development to help readers understand cardiac risks.