Getting sick while pregnant doesn’t automatically put your baby at risk, but your body handles illness differently during pregnancy. Your immune system shifts in ways that can make certain infections harder to shake, fever poses specific risks depending on your trimester, and many common medications are off the table. Here’s what’s actually going on and what you can do about it.
Why Pregnancy Changes How You Fight Infection
Your immune system isn’t suppressed during pregnancy, despite what you may have heard. It’s recalibrated. Starting in the first trimester, your body gradually shifts from aggressive, inflammation-driven immune responses toward a quieter, antibody-based defense. This protects the baby (who is, immunologically speaking, half foreign tissue) but changes how effectively you fight off certain pathogens.
Some of the specific changes: your white blood cells called neutrophils increase in number but become less effective when activated. Your B cells, which produce antibodies, drop significantly by the third trimester and respond less strongly to infections. Even the antibodies you do produce get modified in ways that reduce their ability to tag infected cells for destruction. Meanwhile, your body is also dealing with physical changes. Your lungs have less room to expand as the uterus grows, and blood volume increases by nearly 50%. These shifts mean a respiratory infection like the flu can progress to pneumonia more easily, and urinary tract infections become more common because of changes in how urine flows through the kidneys.
None of this means every cold will become dangerous. Most pregnant people recover from common viruses without complications. But your threshold for “this is getting worse” should be lower than it would be otherwise.
What Fever Does to a Developing Baby
Fever is the main concern with any illness during pregnancy, especially in the first trimester. A sustained maternal temperature above 103°F (39.5°C) during early pregnancy increases the risk of miscarriage and neural tube defects, which are problems with how the brain and spinal cord form. High heat disrupts protein production in developing cells and can cause cell death, blood vessel damage, and problems with the placenta.
This doesn’t mean a brief low-grade fever will cause birth defects. The risk is tied to how high the temperature climbs and how long it stays elevated. Keeping a fever below 100.4°F with acetaminophen (Tylenol) is considered safe throughout pregnancy and is the single most important thing you can do when you’re sick with a fever.
Infections That Carry Higher Risk
Most colds and stomach bugs pass without harming the pregnancy. A handful of infections, though, deserve extra vigilance.
Influenza
The flu hits pregnant people harder. Changes to your immune system, heart, and lungs make you more likely to develop severe illness requiring hospitalization. Flu vaccination during pregnancy cuts the risk of getting the flu roughly in half and reduces the chance of flu-related hospitalization by about 40%. The vaccine is recommended during any trimester.
Listeriosis
Listeria is a bacterial infection picked up from contaminated foods like deli meats, soft cheeses, and unpasteurized products. What makes it deceptive is that symptoms in pregnant people are usually mild: a fever, muscle aches, fatigue. Some people have no symptoms at all. But the infection can cross the placenta and lead to miscarriage, stillbirth, premature delivery, or a life-threatening infection in the newborn. If you develop an unexplained fever after eating a high-risk food, mention the possibility of listeria specifically.
RSV
A maternal RSV vaccine (Abrysvo) is now recommended between 32 and 36 weeks of pregnancy. The goal isn’t to protect you during pregnancy but to pass antibodies to the baby before birth, shielding the newborn during the first months of life when RSV is most dangerous. Getting the vaccine after 36 weeks doesn’t leave enough time for antibodies to transfer.
Medications You Can and Can’t Take
The biggest adjustment for most people is realizing how many everyday medications are restricted. Here’s the practical breakdown.
Acetaminophen (Tylenol) is the go-to for pain and fever throughout all three trimesters. It has decades of widespread use in pregnancy with very few documented adverse effects.
Ibuprofen, aspirin, naproxen, and other NSAIDs should be avoided after 20 weeks of pregnancy. The FDA warns that these medications can cause rare but serious kidney problems in the developing baby, leading to dangerously low amniotic fluid levels. After 30 weeks, NSAIDs carry an additional risk of causing premature closure of a blood vessel near the baby’s heart. The one exception is low-dose aspirin (81 mg), which is sometimes prescribed for specific pregnancy complications and remains safe when directed by a provider.
For cold and congestion symptoms, the options narrow but don’t disappear entirely. Chlorpheniramine (Chlor-Trimeton) is considered the preferred antihistamine. The cough suppressant dextromethorphan (found in many “DM” cough syrups) appears safe based on available evidence. Oral decongestants containing pseudoephedrine are generally classified as low risk but are best avoided during the first trimester due to a possible association with a rare abdominal wall defect.
Always check active ingredients on combination cold products. Many contain NSAIDs or multiple drugs you may not need.
Staying Hydrated When You Can’t Keep Food Down
Dehydration is a real and underestimated risk when illness overlaps with the nausea that pregnancy already brings. Your blood volume is expanded, your kidneys are working harder, and vomiting or diarrhea from a stomach bug can tip you into dehydration faster than usual.
Watch for dark urine, dry skin, persistent lightheadedness, weakness, or fainting. These are signs your fluid levels have dropped too far. If you can’t keep any fluids down for more than 8 to 12 hours, or you haven’t been able to eat for more than 24 hours, that crosses into territory where you likely need IV fluids. Small, frequent sips of water, electrolyte drinks, or even ice chips are easier to tolerate than drinking a full glass at once.
Warning Signs That Need Immediate Attention
Some symptoms during illness overlap with serious pregnancy complications like preeclampsia or placental problems. The CDC identifies several warning signs that warrant immediate medical care, whether or not you think they’re related to being sick:
- Fever of 100.4°F or higher that doesn’t respond to acetaminophen
- Severe headache that won’t go away, gets worse, or comes with blurred vision or dizziness
- Trouble breathing that feels like you can’t get enough air, tightness in your chest or throat, or difficulty breathing while lying flat
- Changes in your baby’s movement, specifically any noticeable decrease from their normal pattern
- Severe nausea and vomiting where you can’t keep water down for 8 hours or food for 24 hours
- Vaginal bleeding or fluid leaking beyond light spotting
- Chest pain or a racing, pounding, or irregular heartbeat
A regular cold with sneezing and congestion is not an emergency. But pregnancy lowers your margin for error with respiratory infections, high fevers, and dehydration. The line between “riding it out” and “getting checked” is closer than it would be when you’re not pregnant, and there’s no downside to calling your provider early if something feels off.