Getting sick repeatedly during pregnancy is one of the most common complaints expectant parents have, and it’s not bad luck. Your immune system fundamentally changes the way it operates during pregnancy, making you more vulnerable to colds, flu, urinary tract infections, and yeast infections. On top of that, hormonal shifts physically alter your respiratory and urinary tracts in ways that invite infection. Understanding what’s happening in your body can help you tell the difference between normal pregnancy-related illness and something that needs attention.
Your Immune System Works Differently Now
The core reason you keep catching every bug going around is that your body has deliberately dialed down part of its immune defense. During pregnancy, your immune system shifts away from the type of response that attacks foreign cells and toward a more tolerant mode designed to protect the fetus. Your baby carries half of its father’s genetic material, which means it’s technically foreign tissue. To prevent your body from rejecting it, pregnancy hormones like progesterone and estrogen actively promote this shift in immune balance.
This tolerance comes at a cost. The branch of your immune system responsible for fighting off viruses, bacteria, and other invaders becomes less aggressive. The trade-off is real and measurable: pregnant people are four to five times more susceptible to influenza A than non-pregnant people, and those in the third trimester are five times more likely to be hospitalized with the flu than those in early pregnancy or postpartum. During the early stages of the COVID-19 pandemic, hospitalization rates among pregnant individuals were roughly 31.5%, compared to 5.8% for non-pregnant people of similar age.
Not every infection hits harder during pregnancy. Some viral illnesses, like Zika, tend to follow a similar course regardless of pregnancy status. And one systematic review found that pregnant individuals actually reported lower rates of cough, sore throat, fatigue, and headache with certain infections compared to non-pregnant people. But on balance, your immune system is simply not operating at full capacity, especially in the second and third trimesters.
Hormones Change Your Nose, Throat, and Airways
Even when you don’t have an actual infection, pregnancy can make you feel constantly congested. Rising estrogen levels cause the blood vessels in your nasal lining to swell, leading to thickened tissue, excess mucus production, and a persistent stuffy feeling. Estrogen receptors sit right in the nasal mucosa, and as estrogen climbs in the second and third trimesters, it increases vascular permeability and triggers the tissue to swell, even without any inflammation or infection present.
Progesterone contributes too. Known for relaxing smooth muscle in the uterus, it also relaxes blood vessels in the upper respiratory tract, reducing vascular tone and increasing blood flow to nasal tissue. The result is mucosal swelling that narrows your nasal passages. Histological studies of the nasal passages during pregnancy show dilated venous structures and thickened mucosal tissue, a passive vascular process rather than an allergic or infectious one.
This chronic congestion does more than make you uncomfortable. The combination of swollen tissue, increased glandular secretion, and changes in mucus composition slows down your nasal cilia, the tiny hair-like structures that sweep germs and debris out of your airways. When mucociliary transport slows, pathogens linger longer, giving them a better foothold. So that cold you caught doesn’t just feel worse because of existing congestion. Your body is also less efficient at clearing it.
Urinary Tract Infections Become More Likely
If you’ve had one or more UTIs since becoming pregnant, the anatomy of your urinary system is largely to blame. Progesterone relaxes the smooth muscle throughout the urinary tract, including the ureters (the tubes connecting your kidneys to your bladder). This relaxation slows the flow of urine and allows it to pool, creating a warm, stagnant environment where bacteria thrive. At the same time, the growing uterus compresses the bladder, reducing its capacity and making it harder to fully empty.
These changes create a chain reaction: urine sits longer in the bladder, residual urine remains after you think you’ve emptied it, and urine can even flow backward from the bladder toward the kidneys. Hormonal shifts also alter the vaginal flora, potentially increasing the number of bacteria near the urethra that are capable of causing infection. All of this means that what might have been a once-a-year inconvenience before pregnancy can become a recurring problem.
Sleep Disruption Weakens Your Defenses Further
Pregnancy-related insomnia, hip pain, frequent urination, and general discomfort mean that most pregnant people aren’t sleeping well, especially in the third trimester. This matters for your immune system more than you might think. Even a single night of shortened sleep (four to eight hours less than normal) is associated with measurable declines in immune cell activity. Chronic sleep deprivation also increases circulating levels of inflammatory markers, creating a state of low-grade inflammation that diverts immune resources away from fighting actual infections.
The compounding effect is significant. You’re already working with a dampened immune system, breathing through swollen nasal passages, and running on broken sleep. Each factor alone increases your vulnerability to illness. Together, they explain why you might feel like you’re catching a cold every few weeks.
Managing Cold and Flu Symptoms Safely
Treating illness during pregnancy requires more caution than usual, because many common over-the-counter cold medications aren’t recommended. Here’s what’s generally considered acceptable based on current guidelines:
- Saline nasal rinses: Safe and effective for reducing congestion without any medication.
- Oral antihistamines: Cetirizine (Zyrtec) and loratadine are the preferred options for congestion related to allergies or rhinitis.
- Nasal steroid sprays: Budesonide is the most studied option in pregnancy and is considered acceptable for chronic or allergic congestion.
- Cough suppressants: Dextromethorphan (the “DM” in many cough syrups) is generally considered safe, with no observed increase in birth defects based on historical use.
Two categories to avoid: stimulant decongestants (like pseudoephedrine and phenylephrine), which carry a possible risk of congenital malformations, and guaifenesin, an expectorant with weak human safety data and a possible association with neural tube defects.
When a Fever Needs Attention
Most colds and mild viral infections will resolve on their own, even if they take a bit longer during pregnancy. Fever is the signal to pay closer attention. A maternal temperature of 38°C (100.4°F) or above is considered clinically significant during pregnancy. At 39°C (102.2°F) or higher, medical evaluation becomes more urgent, as sustained high fevers can affect fetal development, particularly in the first trimester.
Beyond fever, signs that warrant a call to your provider include painful or burning urination (which may signal a UTI that could progress to a kidney infection), a cough that produces colored mucus or lasts longer than 10 days, difficulty breathing, or any illness accompanied by severe vomiting that prevents you from staying hydrated. UTIs in particular should not be ignored during pregnancy, because untreated infections can ascend to the kidneys and trigger preterm labor.
Practical Ways to Reduce Your Risk
You can’t reverse the immune shift that pregnancy creates, but you can reduce how often you’re exposed to pathogens and support the immune function you do have. Frequent handwashing remains the single most effective way to prevent respiratory and gastrointestinal infections. Avoiding close contact with sick family members or coworkers, when possible, matters more now than it did before pregnancy.
Prioritizing sleep, even if it means napping during the day to compensate for disrupted nights, helps maintain immune cell activity. Staying well-hydrated thins mucus secretions and supports kidney function, both of which reduce your risk of respiratory and urinary infections. Emptying your bladder frequently and fully (leaning forward at the end of urination can help) reduces the stagnant urine that bacteria feed on.
The flu vaccine is one of the most impactful steps you can take. Because pregnant people are significantly more likely to be hospitalized with influenza, vaccination provides protection during a period when your body is least equipped to handle the virus on its own. The antibodies you produce also cross the placenta, giving your baby some protection during their first months of life.