Getting sick while pregnant doesn’t automatically harm your baby, but your body handles illness differently during pregnancy. Your immune system shifts to protect the growing fetus, which can make infections hit harder and last longer than they normally would. The biggest concerns are prolonged high fever, dehydration, and a handful of specific infections that can cross the placenta.
How serious an illness becomes depends on what you’ve caught, how far along you are, and how quickly you manage symptoms. Most common colds and stomach bugs pass without affecting the pregnancy at all. But understanding which situations need attention can help you act quickly when it matters.
Why Pregnancy Changes How Your Body Fights Illness
Your immune system doesn’t shut down during pregnancy, but it does recalibrate. Early on, the embryo triggers a wave of specialized immune cells that migrate to the uterus and dial back the body’s tendency to attack foreign tissue. This is essential because half of your baby’s DNA comes from someone else, and without this shift, your immune system would treat the pregnancy like an invader.
The tradeoff is real but often misunderstood. Pregnancy doesn’t necessarily make you more likely to catch a cold or the flu. What it does is raise the stakes when you do get sick. Your body’s recalibrated immune response can overreact or underreact to infections, leading to greater disease severity. The threshold for when a normal immune response tips into a dangerous one is lower during pregnancy. This is why the same virus that gives your partner a rough weekend could land you in the hospital.
The Flu and COVID-19 Carry Higher Risks
Influenza and COVID-19 are the two respiratory infections that pose the most well-documented threats during pregnancy. CDC data comparing pregnant and nonpregnant women of the same age found that pregnant women with COVID-19 had five times the risk of ICU admission and a 76% increased risk of needing mechanical ventilation. Both infections also increase the chance of preterm delivery (before 37 weeks) and stillbirth.
These numbers don’t mean every pregnant person with the flu or COVID ends up in the hospital. Most recover at home. But they explain why the flu vaccine is recommended during every pregnancy, regardless of trimester. The Tdap vaccine, which protects against whooping cough, is also recommended between 27 and 36 weeks of each pregnancy to pass protective antibodies to the baby before birth. A newer RSV vaccine is now recommended as a single dose between 32 and 36 weeks during RSV season (September through January in most of the U.S.) to protect infants in their first months of life.
Fever, Dehydration, and Why They Matter
A sustained high fever is one of the main ways a routine illness can affect your baby. Elevated maternal body temperature, particularly in the first trimester, has been linked to certain birth defects. Bringing a fever down promptly is a priority. Acetaminophen (Tylenol) remains the go-to pain and fever reducer throughout pregnancy.
Dehydration is the other major concern, especially with stomach bugs that cause vomiting or diarrhea. Your blood volume increases by nearly 50% during pregnancy, and your body uses that fluid to maintain amniotic fluid levels. When you’re dehydrated, amniotic fluid can drop, a condition called oligohydramnios. Studies suggest that rehydrating can help restore those levels, but persistent vomiting that prevents you from keeping fluids down for more than eight hours is a red flag that needs medical attention.
Foodborne Infections That Can Reach the Baby
Most viruses that cause the common cold don’t cross the placenta. But a few foodborne pathogens can, and they deserve special attention.
Listeria is the most serious. Pregnant women are roughly 10 times more likely to get listeriosis than the general population. The tricky part is that you might feel only mildly ill, with flu-like symptoms such as fever and muscle aches, or you might not feel sick at all. Meanwhile, the bacteria can cross the placenta and cause miscarriage, stillbirth, premature delivery, or life-threatening infection in the newborn, including meningitis. In late-term fetuses, listeria infection can lead to seizures, intellectual disability, and damage to the brain, heart, or kidneys. This is why the standard advice to avoid deli meats, unpasteurized cheese, and smoked seafood during pregnancy exists. It’s not overcautious; the consequences are severe even when maternal symptoms are mild.
Toxoplasmosis, caused by a parasite found in undercooked meat and cat feces, poses similar risks of crossing the placenta and causing developmental problems. Cooking meat thoroughly and having someone else handle the litter box are practical steps that meaningfully reduce your risk.
What You Can and Can’t Take for Cold Symptoms
The biggest medication restriction during pregnancy involves ibuprofen (Advil, Motrin) and other NSAIDs like naproxen. The FDA recommends avoiding all NSAIDs after 20 weeks of pregnancy because they can reduce amniotic fluid levels. After 30 weeks, NSAIDs can cause premature closure of a blood vessel in the baby’s heart that needs to stay open until birth. Acetaminophen is the safer alternative for pain and fever.
For congestion, nasal sprays containing oxymetazoline (like Afrin) are generally considered lower risk than oral decongestants because less of the drug reaches the baby. Keep use under three days. Oral decongestants like pseudoephedrine and phenylephrine have been associated with birth defects when used in the first trimester and are best avoided early on. If needed later in pregnancy, short-term use of a few days may be considered.
For coughs, dextromethorphan (the “DM” in many cough syrups) is commonly used, though you should choose alcohol-free formulations. The expectorant guaifenesin (Mucinex) is generally considered acceptable in the second and third trimesters, but one study found an association with hernia in offspring when used in the first trimester. Throat lozenges containing benzocaine or menthol are options for sore throat relief.
The overarching principle: fewer medications and shorter courses are better, and checking with your provider before taking anything combination-formula is worth the phone call, since many cold medicines bundle multiple active ingredients together.
If You Need Imaging or Testing
If you develop pneumonia, a severe cough, or abdominal pain while pregnant, your doctor may need X-rays or a CT scan to figure out what’s going on. Many people worry about radiation exposure, but the American College of Obstetricians and Gynecologists is clear on this: standard diagnostic imaging exposes the fetus to radiation doses far below the level associated with harm, and necessary imaging should not be withheld from a pregnant patient. Ultrasound and MRI involve no radiation and are preferred when they can answer the clinical question, but an X-ray or CT scan that your doctor recommends is not something to refuse out of fear for the baby. Delaying a diagnosis is usually the bigger risk.
Warning Signs That Need Immediate Attention
Most colds and mild stomach bugs will pass in a few days with rest and fluids. But certain symptoms during pregnancy signal that something more serious may be happening:
- Inability to keep fluids down for more than 8 hours, or food for more than 24 hours. Signs of dehydration include dry mouth, dizziness, confusion, and dark urine.
- Trouble breathing that comes on suddenly or worsens over time, especially if you feel like you can’t get a deep enough breath or need to prop yourself up with pillows to sleep.
- A change in your baby’s movement pattern. There’s no magic number of kicks to count. What matters is a noticeable decrease from what’s been normal for your baby.
- Fever above 101°F (38.3°C) that doesn’t respond to acetaminophen or that persists for more than 24 hours.
These aren’t reasons to panic, but they are reasons to call your provider promptly rather than waiting it out. Pregnancy narrows the margin between “uncomfortable but fine” and “needs intervention,” and early treatment almost always leads to better outcomes for both you and the baby.