Influenza in pregnant women: risks for mom and baby, safe treatment

Influenza in pregnant women is not just a "cold with a fever," but a serious viral disease that can cause complications for both the future mother and the child. The influenza virus attacks the respiratory tract, causing fever, aches, cough, and weakness, but during pregnancy, these symptoms can lead to much more dangerous consequences: pneumonia, premature birth, low birth weight, or even intrauterine hypoxia. A woman's body during pregnancy is in a special physiological state: the immune system intentionally "slows down" to avoid rejecting the fetus. This makes her vulnerable to infections—especially acute respiratory viruses, including influenza. And while a healthy person usually recovers in 7-10 days, the risk of complications increases significantly for pregnant women. The third trimester and the first weeks after childbirth are particularly dangerous—this is when the load on the cardiovascular and respiratory systems is at its maximum.

Classification of the disease according to ICD-10

According to the International Classification of Diseases, 10th Revision (ICD-10), influenza falls under the category "Viral infections of the respiratory tract" and is coded as J09–J11Specifically:

• J09 — influenza caused by identified influenza virus A (e.g., H1N1, H5N1);
• J10 — influenza caused by identified influenza virus B;
• J11 — influenza, virus not identified ("unspecified" influenza).

For pregnant women, additional coding from the block O98–O99 — "Infectious and parasitic diseases complicating pregnancy, childbirth, and the postpartum period." In particular, O98.5 — "Influenza complicating pregnancy." This code is critical for medical statistical reporting and affects the priority of care: with its presence, the patient automatically falls into the high-risk group and receives enhanced monitoring.

History of the disease and interesting historical facts

Influenza has been known to humanity since ancient times. The first reliable description of an epidemic resembling influenza dates back to 412 BC, when Hippocrates described "fever with cough and shortness of breath" in Greece. But a real breakthrough in understanding the disease occurred only in the 20th century.
In 1918, the "Spanish flu" broke out — a pandemic of influenza A(H1N1) that claimed the lives of 50 million people worldwide. The peculiarity of this wave was the high mortality among young adults, including pregnant women. Studies in the 2000s showed: among women in position, mortality reached 25–30%, while in the general population it was about 2%. The reason was a combination of immunosuppression, hyper-inflammatory response, and a sharp increase in blood volume, which overloaded the lungs and heart.
Another curious fact: in 1957, during the "Asian flu" pandemic (A/H2N2), doctors in the USA first used an antiviral drug — amantadine. It proved effective against the influenza A virus, but not B. Later, it was found that the virus mutates rapidly — by the end of the 1960s, most strains had become resistant to it. Today, amantadine is hardly used, while oseltamivir and zanamivir have come to replace it — drugs that block neuraminidase, an enzyme without which the virus cannot exit the cell.

Epidemiology: statistics on the occurrence of the disease

Every year, between 5 to 15% of the world's population gets infected with influenza — that’s 290–650 million people. According to WHO, seasonal outbreaks lead to 3–5 million cases of severe complications and 290–650 thousand deaths annually. Pregnant women have a hospitalization risk 4–10 times higher than non-pregnant women of the same age.
In Russia, between 20 to 40 million cases of ARVI and influenza are registered annually. According to Rospotrebnadzor for 2023–2024, among those hospitalized with influenza, 12–18% were pregnant women. Of these cases, 60–70% occurred in the third trimester. Interestingly, during the COVID-19 pandemic, the incidence of influenza sharply declined — due to mask mandates, quarantines, and social distancing. However, since 2022, the return of the "usual" flu season has become particularly aggressive: in the 2023/24 season, the A(H1N1)pdm09 strain dominated, which is especially dangerous for young people and pregnant women.
It is important to understand: influenza is not just a winter phenomenon. In countries with a tropical climate, it circulates year-round, while in temperate latitudes — from October to May, peaking in January–February. For pregnant women, the risk of infection increases not only due to the season but also due to visits to clinics where many infected individuals are present.

Genetic predisposition to influenza

There is no direct "flu gene" — the incidence is determined not by genetics in pure form, but by a combination of genetic variants that affect the immune response. Studies show that certain polymorphisms in genes encoding receptors for interferons (for example, IFITM3) increase susceptibility to severe influenza.
The gene IFITM3 is responsible for synthesizing a protein that blocks the virus from entering the cell. In carriers of the rs12252-C variant, the risk of developing pneumonia with influenza increases sixfold. Another gene — TLR7, involved in recognizing RNA viruses. Mutations here are more common in men and are associated with severe disease, but the role of TLR7 in pregnant women is still not fully understood.
It is also important: women with certain HLA alleles (for example, HLA-DRB1*15:01) exhibit a weaker T-cell response to the influenza virus. This does not mean they are "doomed" to get sick — it simply means their immune system may respond more slowly. Therefore, prevention and early treatment are critical for them.

Risk factors for influenza in pregnant women

Risk factors can be divided into three groups: biological, behavioral, environmental.
Biological:

• Decreased cellular immunity (reduced activity of T-lymphocytes and NK cells);
• Physiological increase in the volume of circulating blood (+40–50 %), which increases the load on the lungs;
• Diaphragm displacement upwards due to the growth of the uterus — reduction of lung vital capacity %;
• Hormonal changes: progesterone suppresses the inflammatory response, estrogens enhance the expression of virus receptors in the respiratory epithelium.

Behavioral:

• Refusal of vaccination (often due to myths about "harm to the fetus");
• Frequent trips on public transport, visiting clinics without a mask;
• Lack of sleep and chronic stress — reduce interferon production.

Environmental:

• Living in an apartment building with a large number of neighbors;
• Working in educational or medical institutions;
• Seasonal circulation of the virus (especially when coinciding with the epidemic threshold).

Note: even if you do not leave the house, there is a risk — through your husband, children, couriers. The virus remains on surfaces for up to 48 hours, and in the air — up to 1 hour under normal humidity.

Diagnosis of influenza in pregnant women

The diagnosis is made based on the clinical picture and laboratory confirmation. In pregnant women, symptoms may be "masked" — for example, fever below 38 °C, but with pronounced weakness and shortness of breath. This is called "atypical course" and often leads to delayed diagnosis.
Main symptoms:

• Acute onset (within 1–2 hours): headache, body aches, chills;
• Temperature ≥38 °C (may be subfebrile — 37.5–38.0 °C in some);
• Dry cough, sore throat, nasal congestion (more often secondary);
• Shortness of breath with physical exertion — a worrying signal, especially in the third trimester;
• Increased heart rate (>100 beats/min) — may indicate the early stage of pneumonia.

Laboratory tests:

Radiological examinations:
Chest X-ray when pneumonia is suspected is done with abdominal protection (lead shield). Modern machines give a dose of 0.01–0.03 mSv — this is safe for the fetus (the risk threshold starts at 100 mSv). CT — only for vital indications, with a minimal dose.
Differential diagnosis:
It is necessary to distinguish influenza from:

• ARVI (usually without fever above 38.5 °C, severe chills and aches);
• COVID-19 (often with anosmia, diarrhea, longer cough);
• Bacterial pneumonia (temperature lasts >5 days, purulent sputum);
• Toxicosis of the second half of pregnancy (preeclampsia) — there is no cough, but there are edema, proteinuria, and BP >140/90.

Treatment of influenza in pregnant women

Treatment should begin **within the first 48 hours** after the onset of symptoms. The earlier, the higher the chance of avoiding complications. The main rule: no self-medication. No "hot tea with honey," no "paracetamol at 3 tablets" — only as prescribed by a doctor.
General treatment:

• Bed rest — even with a mild course. In a side position (preferably on the left), blood flow to the placenta improves;
• Abundant drinking — at least 2 liters/day: water, dried fruit compote, herbal teas (chamomile, mint — without St. John's wort and thyme);
• Humidification of the air — 50–60 % humidity reduces viral load in the room;
• Temperature control — at ≥38.5 °C, fever should be reduced (see below).

Pharmacological treatment:
The basis is antiviral drugs based on **oseltamivir** (Tamiflu®). It is prescribed at a dose of 75 mg twice a day for 5 days. Effectiveness is confirmed by WHO and the Ministry of Health of the Russian Federation: when used in a timely manner, it reduces the risk of hospitalization by 60 % and shortens the duration of fever by 1–2 days.
Important: oseltamivir is allowed from the first trimester. In 2011, a study on 5500 pregnant women was published in Lancet — no side effects were found in the mother or fetus. Zanamivir (Relenza®) — inhalational, less studied in pregnant women, therefore used only in case of intolerance to oseltamivir.
Fever reduction:
Paracetamol is the only approved antipyretic. Dose — 500 mg every 6 hours (max. 4 g/day). Ibuprofen, aspirin, and analgin cannot be used — they increase the risk of bleeding and fetal development disorders.
Surgical treatment:
It is not used for influenza as such. But in case of complications — for example, lung abscess or pleural empyema — drainage may be required. In such cases, the decision is made by a multidisciplinary team: obstetrician-gynecologist, pulmonologist, anesthesiologist.

List of medications used for influenza in pregnant women

Here is a verified list of medications approved and recommended by the Ministry of Health of the Russian Federation and WHO for use during pregnancy:

Prohibited drugs:

• Aspirin — risk of Reye's syndrome in children and bleeding;
• Ibuprofen and other NSAIDs — especially in the III trimester (risk of premature closure of the ductus arteriosus);
• Amantadine and rimantadine — outdated, virus resistance >99 %;
• Antibiotics without indications do not treat viruses, but disrupt the microflora and increase the risk of fungal infections.

Disease monitoring: control stages, prognosis, complications

After diagnosis and the start of treatment, regular monitoring is necessary. Here are the key steps:
Day 1–2:
— Temperature control every 4 hours;
— Assessment of respiratory function: respiratory rate >20 per minute is a warning sign;
— Ultrasound of the fetus (if there are complaints of decreased movements).
Day 3–4:
— If the temperature does not decrease, a repeat PCR and X-ray are needed;
— Blood test: leukocytes, C-reactive protein, platelets (risks of DIC syndrome);
— Blood pressure monitoring — hypertension may indicate preeclampsia against the background of infection.
Day 5–7:
— If improvement occurs — continue therapy until the end of the course;
— If deterioration occurs — hospitalization in an infectious or obstetric department.
Forecast:
With timely treatment, 90-95% of pregnant women with influenza recover without consequences. But without therapy, the risk of complications increases:

• Pneumonia occurs in 5-10% of pregnant women with influenza;
• Premature birth occurs in 15-20% in cases of severe illness;
• Intrauterine growth retardation occurs with fever >39 °C for more than 24 hours;
• Neonatal infection occurs if the mother fell ill 1-2 days before delivery (transmission during childbirth).

Fetal hypoxia is particularly dangerous: fever reduces blood oxygen saturation, and the growing uterus compresses the inferior vena cava — this leads to a temporary decrease in blood flow through the placenta. That is why shortness of breath in a pregnant woman is not "fatigue," but a signal to take action.

Age-related features of influenza in pregnant women

Influenza in pregnant women is not the same at 20 and 35 years old. Age affects the immune system's response and accompanying conditions.
Young pregnant women (under 25 years):**
They often experience influenza more easily, but the risk of "hyper-inflammatory storm" is higher — when the immune system attacks not only the virus but also its own tissues. This can lead to acute respiratory distress syndrome (ARDS) even without pneumonia. They more frequently encounter the H1N1 strain — it aggressively affects the lungs of young individuals.
Middle age (26-35 years):**
The largest group of pregnant women. Here, the key factor is the presence of chronic diseases: bronchial asthma, diabetes, obesity. For example, with a BMI >30, the risk of hospitalization increases by 3 times. Vaccination status is also important: if a woman received the vaccine last year, the illness will be milder.
Older age (36+ years):**
The risk of complications increases not because of the flu itself, but due to age-related changes: decreased lung function, arterial hypertension, metabolic disorders. These women are more likely to develop bacterial superinfection — for example, pneumococcal pneumonia. There is also an increased risk of thrombosis, especially if there is varicose veins or a predisposition to DIC.
An interesting point: the risk is higher in primiparous women than in multiparous women. Probably because the body is adapting to the immunosuppressive state for the "first time," and the protective mechanisms are not yet established.

Can a flu vaccine be given during pregnancy?
Yes, and it is strongly recommended. Vaccination is carried out from the first trimester (from 12 weeks — optimally), but during an epidemic threshold — even earlier. Only inactivated vaccines are used (for example, "Grippol Plus," "Influvac"). They do not contain live virus, so they cannot cause the flu. According to WHO data, vaccination reduces the risk of illness by 50% and severe complications by 70%. In newborns, passive immunity is formed through the placenta and breast milk in the first 6 months.
What to do if the temperature does not decrease after paracetamol?
Do not increase the dose! More than 4 g/day — risk of toxic liver damage. Do the following:

• Wipe the forehead, wrists, and armpits with cool water (not alcohol!);
• Place a cold compress on the forehead;
• Call a doctor — intravenous therapy or hospitalization may be needed;
• If the temperature is ≥39.5 °C for more than 6 hours — this is an indication for urgent hospitalization.

Can the flu cause a miscarriage?
There is no direct link "flu → miscarriage," but there is an indirect one. High fever (≥39 °C for more than 24 hours), severe intoxication, and hypoxia can provoke uterine contractions and disrupt placental blood flow. The first trimester is especially dangerous — when the organs of the fetus are being formed. Therefore, in the first 12 weeks, if there is any suspicion of the flu — contact a doctor immediately.
Is it safe to breastfeed with the flu?
Yes, and it is even recommended. The virus is not transmitted through milk. On the contrary, the antibodies produced by the mother enter the milk and protect the child. But while breastfeeding, wear a mask, wash your hands, and avoid coughing near the baby. If you are in a hospital — you can pump milk and give it through a bottle.

Typical mistakes and how to avoid them

Mistake 1: "I'll wait a couple of days — it will pass on its own"**
The flu in pregnant women does not "just pass." Within 48 hours, the virus has already invaded the cells, and every hour of delay increases the risk of pneumonia.
How to avoid: At the first symptoms — call a doctor, PCR test, if confirmed — oseltamivir on the same day.
Mistake 2: "I'll take ibuprofen — it's stronger than paracetamol"**
Ibuprofen in the third trimester blocks the synthesis of prostaglandins necessary for cervical dilation and water breaking. This can lead to delayed labor and hypoxia.
How to avoid: Remember: only paracetamol. Keep it in the first box of your medicine cabinet.
Error 3: "Vaccination is for others, I'm healthy anyway"**
Even if you are not sick, the virus can reach you through your child or husband. And vaccination is not only your protection but also the protection of your future child.
How to avoid: Sign up for a vaccination at the clinic in advance — during the season it ends by November.
Error 4: "I will rinse my nose with soda and everything will pass"**
Soda irritates the mucous membrane, causes dryness and microcracks — this facilitates the penetration of the virus.
How to avoid: use only isotonic sea water solution (Aqualor, Physiomer) or saline solution.

Remember: you are not alone. Over the past 10 years, clear protocols for managing pregnant women with influenza have been developed in Russia. And if you follow the recommendations — the chances of a healthy child and a quick recovery are very high. Your task is not to "survive," but to **start treatment on time**. And we are here to help you do it right.