A fishy smell during pregnancy is most commonly caused by bacterial vaginosis (BV), a vaginal infection that affects roughly 1 in 5 pregnant women. It can also come from hormonal shifts that change your vaginal discharge, increased sweating, or even your diet. While the smell itself is unpleasant, it’s worth paying attention to because certain causes need treatment to protect your pregnancy.
Bacterial Vaginosis: The Most Likely Cause
Bacterial vaginosis is an overgrowth of certain bacteria that naturally live in the vagina. When the balance tips away from protective bacteria (lactobacillus) and toward other species, the result is often a thin, grayish-white discharge with a distinctly fishy odor. That smell comes from a specific chemical called trimethylamine, the same compound responsible for the odor of spoiling fish. Your body produces it when certain bacteria break down substances in the vaginal environment.
The smell tends to be strongest after sex and after your period, because semen and menstrual blood are both slightly alkaline, which releases more of the odor-causing chemical into the air. If you’ve noticed the smell gets worse at those times, BV is a strong possibility.
Pregnancy itself makes BV more likely. Rising estrogen levels increase the amount of glycogen (a sugar) in vaginal tissue, which changes the environment bacteria live in. These hormonal shifts can also alter the acid-base balance of the vaginal lining, making it easier for BV-associated bacteria to take hold. Globally, BV prevalence in pregnant women ranges from about 12% to 49% depending on the population studied, with an average around 25%.
Why BV Matters During Pregnancy
BV isn’t just a nuisance. Left untreated in pregnancy, it’s associated with premature rupture of membranes, preterm birth, low birth weight, and infection of the amniotic fluid. The CDC recommends treatment for all pregnant women with symptomatic BV specifically because of these risks. Treatment typically involves a course of oral antibiotics taken for about seven days, with cure rates around 70% to 85% depending on the specific regimen. These medications are considered safe during pregnancy.
The important thing to know: you don’t need to feel embarrassed bringing this up with your provider. It’s one of the most common infections in pregnancy, and a quick office test can confirm or rule it out.
Trichomoniasis: Another Infection to Rule Out
Trichomoniasis, a sexually transmitted infection caused by a parasite, can also produce a fishy or unpleasant vaginal odor. The key differences from BV are in the discharge itself. Trichomoniasis typically causes a bubbly, yellow-green, profuse discharge along with intense vulvar irritation, redness, and burning. BV discharge tends to be thinner, white or gray, and less irritating.
If you’re experiencing itching, burning, or redness alongside the fishy smell, trichomoniasis is worth investigating. Your provider can identify it through a vaginal swab, though the standard microscope test catches it only about 50% to 65% of the time, so more sensitive tests may be needed.
Hormonal Changes and Increased Discharge
Not every change in vaginal smell during pregnancy points to infection. Pregnancy hormones dramatically increase blood flow to the pelvic area and boost vaginal discharge volume, especially in the second and third trimesters. This thicker, more abundant discharge (called leukorrhea) has a mild odor that some women describe as slightly musky or unfamiliar. It shouldn’t smell strongly fishy, though. If the smell is faint and the discharge is white or clear without irritation, it’s likely just a normal pregnancy change.
Diet and Body Odor Shifts
Pregnancy can also change the way your body smells in general, not just vaginally. Hormonal fluctuations increase sweating, and the combination of more sweat with shifting hormones can create unfamiliar body odors, including in the groin area. Some women notice this is worse in the first trimester when hormonal changes are most dramatic.
There’s also a dietary angle worth knowing about. Your body breaks down choline, a nutrient found in eggs, beans, peas, and liver, into trimethylamine, the same fishy-smelling compound involved in BV. Normally, your liver converts this chemical into an odorless form. But if you’re eating large amounts of choline-rich foods or taking high-dose prenatal supplements, the system can get overwhelmed, and the excess trimethylamine comes out in your sweat, breath, and urine with a fishy smell. This is a form of what’s called trimethylaminuria. Cutting back on eggs, legumes, red meat, and certain fish can reduce it noticeably.
What Not to Do About the Smell
The instinct to clean more aggressively is understandable, but douching is one of the worst things you can do. The American College of Obstetricians and Gynecologists is clear on this: do not douche, whether pregnant or not. Douching disrupts the vaginal microbiome, washing away protective bacteria and making infections like BV more likely, not less. Scented soaps, body washes, and vaginal deodorants cause the same problem.
If you feel the need to clean, plain water on the external vulva during a shower is all that’s necessary. Your vagina is self-cleaning. Adding products to the equation almost always makes odor problems worse over time.
What to Watch For
A mild change in how you smell is common in pregnancy and usually harmless. But certain symptoms suggest you should bring it up at your next appointment, or sooner:
- A strong, persistent fishy odor that doesn’t go away with basic hygiene
- Gray, white, or yellow-green discharge that looks different from your normal pregnancy discharge
- Itching, burning, or redness around the vulva or vaginal opening
- Odor that worsens after sex, which is a classic BV pattern
Your provider can typically diagnose the cause with a simple vaginal swab and a few quick tests. If it’s BV, treatment is straightforward and takes about a week. If it’s something else, like trichomoniasis, that’s also treatable during pregnancy. And if the smell turns out to be hormonal or dietary, you’ll have the reassurance of knowing nothing needs medical intervention.