Getting sick while pregnant is common and, in most cases, your body handles it without harm to your baby. A typical cold or mild stomach bug will make you miserable for a few days but rarely causes pregnancy complications. That said, pregnancy does change how your immune system operates, which can make certain infections hit harder or last longer. Knowing what’s routine, what needs treatment, and what counts as an emergency helps you respond calmly.
Your Immune System Works Differently During Pregnancy
A widespread belief is that pregnancy suppresses your immune system, leaving you vulnerable. That’s an oversimplification. Your immune system isn’t weaker during pregnancy. It’s recalibrated. Researchers now describe it as a modulated immune state that shifts through three distinct phases across your trimesters.
During the first trimester, your body runs a pro-inflammatory response to support implantation. The second trimester shifts toward an anti-inflammatory state, which helps your body tolerate the growing fetus. The third trimester swings back toward inflammation as your body prepares for labor. These shifts mean your response to different pathogens changes throughout pregnancy. For example, women in malaria-endemic regions are more susceptible to infection during the first half of pregnancy, with risk dropping in the second half.
The placenta also acts as its own immunological organ. A placental infection that triggers strong inflammation can lead to preterm labor or pregnancy loss. A milder viral infection in the placenta may not cross to the baby directly but can still sensitize your immune system and make you react more strongly to other germs. This is why even routine illnesses deserve a bit more attention when you’re pregnant.
Common Colds and Stomach Bugs
A standard cold with congestion, sore throat, and coughing is not dangerous to your pregnancy. You’ll feel lousy, but the virus itself poses no known risk to fetal development. The priority is staying hydrated, resting, and managing your symptoms safely.
Stomach bugs deserve more caution, not because of the virus itself but because of dehydration. Vomiting and diarrhea can quickly deplete your fluids, and dehydration during pregnancy has real consequences. It can lower amniotic fluid levels and trigger Braxton-Hicks contractions, sometimes earlier than the third trimester. Watch for dark or strong-smelling urine, dizziness, dry mouth, muscle cramping, and extreme thirst. If you can’t keep water down for several hours, that’s a reason to call your provider.
Flu and COVID-19 Carry Higher Stakes
Influenza is one of the infections that genuinely hits pregnant women harder. Meta-analyses show that pregnant women with the flu have 2.36 times higher odds of stillbirth, 1.71 times higher odds of low birth weight, and 1.52 times higher odds of preterm birth. Timing matters: a flu infection during the first trimester doubles the risk of preterm birth and raises the risk of extremely early delivery by about 2.5 times.
COVID-19 poses its own set of risks. Research from the large international INTERCOVID study found a significant link between COVID-19 and preeclampsia, a dangerous blood pressure condition. Symptomatic COVID infections are associated with more severe disruption to blood flow in the placenta, and women who develop both COVID and preeclampsia face higher rates of fetal growth restriction and fetal distress. In severe cases, this combination has been linked to fetal death and, rarely, maternal death.
Neither of these infections is a guaranteed disaster. Most pregnant women with the flu or COVID recover without complications. But both warrant a call to your provider early, because antiviral treatment started within the first 48 hours can reduce the severity and duration of illness.
Infections That Pose Direct Fetal Risk
A handful of infections are particularly dangerous during pregnancy because they can cross the placenta and directly affect fetal development.
- Toxoplasmosis comes from undercooked meat or contact with cat feces. Most infected newborns appear healthy at birth, but some develop mental retardation, blindness, or epilepsy later in life. In severe cases, it causes stillbirth.
- Cytomegalovirus (CMV) spreads through saliva, urine, and other body fluids. It can damage the baby’s central nervous system, kidneys, liver, lungs, and blood-forming system. About 10 to 15 percent of babies with congenital CMV show symptoms at birth, and 6 to 25 percent of those born without symptoms develop problems like hearing loss or cerebral palsy later.
- Listeriosis comes from contaminated food, especially deli meats, soft cheeses, and unpasteurized dairy. It can trigger preterm labor, spontaneous abortion, stillbirth, or severe newborn infection. Late-onset disease in newborns typically shows up as meningitis one to several weeks after birth.
These infections are relatively uncommon, but they’re the reason behind the standard food safety advice you’ve probably already heard: avoid soft unpasteurized cheeses, reheat deli meats until steaming, cook meat thoroughly, wash produce well, and let someone else handle the litter box.
What You Can and Can’t Take for Symptoms
Acetaminophen (Tylenol) is considered safe in all three trimesters for pain and fever. Use the lowest dose that works and avoid making it a daily habit. It does not increase fetal risk when used as a single agent.
Ibuprofen, naproxen, and other NSAIDs are a different story. They’re generally not recommended during pregnancy and should be avoided entirely in the third trimester because they can cause a heart vessel in the baby to close prematurely.
For coughs, dextromethorphan (the “DM” in many cough syrups) appears to be safe. The expectorant guaifenesin has a weak association with certain birth defects and is best avoided in the first trimester. Decongestants containing pseudoephedrine or phenylephrine should also be avoided in the first trimester and used sparingly after that.
If you need antibiotics for a bacterial infection, several classes are well-established as safe during pregnancy, including penicillins (like amoxicillin) and cephalosporins. Tetracyclines, on the other hand, can affect fetal bone growth and discolor developing teeth, so they’re not used after the fifth week of pregnancy. Your provider will know which antibiotic fits your situation.
A good rule for any medication: the first trimester is the most sensitive period for fetal organ development, so limiting unnecessary medication during those early weeks is the most cautious approach.
Vaccines That Protect You and Your Baby
Two vaccines are specifically recommended during pregnancy. The flu shot can be given at any point during flu season, though getting it in September or October during your first or second trimester is ideal. Women in their third trimester may benefit from vaccination as early as July or August, since the antibodies you produce cross the placenta and protect your baby during the first months of life, before they’re old enough to be vaccinated themselves.
The Tdap vaccine, which protects against whooping cough, is recommended during every pregnancy regardless of whether you’ve had it before. The optimal window is between 27 and 36 weeks of gestation, which maximizes the antibodies your baby receives before birth.
Warning Signs That Need Immediate Attention
Most illnesses during pregnancy are manageable at home. But certain symptoms, whether caused by an infection or not, require urgent medical care. The CDC identifies the following as warning signs during pregnancy:
- Fever of 100.4°F (38°C) or higher. A sustained high fever can be harmful to fetal development, especially in the first trimester. Don’t wait it out.
- Inability to keep fluids down for an extended period, especially if accompanied by confusion, dry mouth, or fever.
- Decreased fetal movement or the baby stopping movement entirely.
- Trouble breathing, including sudden shortness of breath, chest tightness, or difficulty breathing while lying down.
- Severe headache that won’t go away, worsens, or comes with blurred vision or dizziness.
- Vaginal bleeding beyond light spotting, or fluid leaking from the vagina.
- Severe belly pain that is sharp, sudden, or getting worse.
- Vision changes like flashes of light, blind spots, or sudden blurriness.
- Extreme swelling in your hands or face, to the point where you can’t bend your fingers or open your eyes fully.
Some of these overlap with symptoms of preeclampsia, which can develop independently or alongside an infection like COVID-19. If you’re sick and something feels off beyond normal illness, err on the side of calling your provider. Pregnancy shifts the threshold for what counts as “worth checking out,” and medical teams expect those calls.