Diarrhea During Pregnancy: Is It Normal and When to Call Your Doctor

Clinically reviewed by Dr. Ponlawat Pitsuwan, Physician, Doctor Samui. Last reviewed: September 2026

You had dinner last night at a beachside restaurant in Chaweng, and this morning you are spending more time in the bathroom than by the pool. If you are pregnant and dealing with diarrhea right now, the first thing to know is that it is genuinely common. It does not automatically mean something is wrong.

That said, pregnancy changes how your body handles infections and fluid loss. What a healthy non-pregnant traveler might shake off in a day can hit harder when you are expecting. This article covers why diarrhea happens in pregnancy, what is safe to eat and drink, which medications to avoid at the pharmacy, and exactly when to stop waiting and call a doctor. If you are in your third trimester, there is a specific section you need to read.

Why Diarrhea Happens During Pregnancy

Pregnancy hormones slow digestion down in the first and second trimesters, which usually causes constipation. But in some women, hormones do the opposite and speed things up, producing loose stools instead. Prenatal vitamins, especially those with high iron content, are another common trigger.

Diet changes play a role too. If you are eating foods you would not normally eat at home, your gut will notice. On Koh Samui, that often means spicier dishes, unfamiliar sauces, coconut milk, or fresh tropical fruit in large amounts. Any of these can loosen stools without an infection being involved.

In the third trimester, the picture shifts. Your body releases prostaglandins, hormone-like chemicals that prepare the uterus for labor. These same chemicals affect the bowel and can cause cramping and diarrhea in the days before labor begins. This is normal, but worth paying close attention to if you are near your due date.

Pregnant Travelers on Koh Samui Face a Different Kind of Risk

This is where standard pregnancy advice falls short. Most articles assume you are at home with your obstetrician a phone call away. On Koh Samui, the situation is different.

Traveler’s diarrhea in pregnancy is not the same as a mild stomach upset at home. Thailand’s tropical heat means bacteria multiply faster in food left at room temperature. Street stalls, hotel buffets, pre-cut fruit, and seafood dishes can all carry pathogens that cause genuine bacterial gastroenteritis. Common culprits include E. coli, Salmonella, and Vibrio from raw or undercooked shellfish.

Pregnancy also adjusts your immune response to protect the baby, which can make it harder to fight off some infections quickly. A bacterial gut infection that a non-pregnant traveler clears in 48 hours may last longer and cause more fluid loss in pregnancy. Add Samui’s heat and humidity to the equation and dehydration can set in faster than you expect.

Can Diarrhea During Pregnancy Harm the Baby?

Short-term diarrhea does not directly harm the baby in most cases. The real risk is dehydration. Pregnant women have a higher fluid requirement than usual, and losing fluids faster than you can replace them puts real stress on the pregnancy.

Severe dehydration can reduce blood flow to the placenta and, in serious cases, trigger uterine contractions. This is why staying ahead of fluid loss matters so much when you are expecting.

Certain infections, particularly Salmonella and Listeria, carry specific risks in pregnancy beyond dehydration and can in rare cases affect the baby directly. If you have eaten high-risk food and you are running a fever alongside diarrhea, this is not something to manage at the hotel. Get assessed the same day.

Food Safety on Koh Samui When You Are Pregnant

The safest food is food that arrives at your table piping hot and freshly cooked. High-turnover restaurants and busy kitchen stalls are generally safer than quiet ones where food sits out. Avoid raw or undercooked shellfish entirely. Mussels, oysters, and clams are common on Samui’s menus and are high risk during pregnancy.

Do not eat from hotel buffets where food has been sitting in warming trays. Pre-cut fruit on market carts in the sun is another risk. Drink only sealed bottled water. Ice at tourist-facing restaurants is usually made from filtered water, but when in doubt, skip it.

These are not rules designed to spoil your holiday. They are the specific risks we see turn into problems at our Chaweng clinic, and they are almost entirely avoidable.

Which Medications Are Safe for Diarrhea During Pregnancy

This is where you need to be careful at a Thai pharmacy. The two most commonly recommended over-the-counter options are loperamide (Imodium) and antibiotics like ciprofloxacin. Both carry concerns in pregnancy.

Loperamide’s safety in the first trimester is not fully established, and most guidelines advise against using it during pregnancy without medical assessment first. Ciprofloxacin and other fluoroquinolone antibiotics are typically avoided in pregnancy. If pharmacy staff offer either of these without asking whether you are pregnant, decline and see a doctor instead.

What is generally safe: oral rehydration salts (ORS), available at any 7-Eleven or pharmacy on Koh Samui. Mix with sealed bottled water, not tap water. Plain boiled rice and ripe banana are easy to find anywhere on the island and are a safe starting point for eating again.

If diarrhea is bacterial and antibiotics are genuinely needed, pregnancy-safe options do exist. Azithromycin, for example, can be appropriate depending on the infection. A doctor needs to make this call, not a pharmacy counter.

Is Diarrhea a Sign of Labor in the Third Trimester?

It can be. In the days before labor begins, prostaglandins cause the bowel to contract and empty. Loose stools in the 24 to 48 hours before labor is actually quite common and is your body clearing itself out naturally.

The key question is what comes with the diarrhea. If it is just loose stools with no other symptoms and you are not yet at full term, a dietary or viral cause is likely. If diarrhea is accompanied by regular cramping, pelvic pressure, lower back pain, increased vaginal discharge, or any fluid leaking, take that seriously. This combination in the third trimester warrants urgent medical review.

Being on Koh Samui near your due date and experiencing these signs together is not a moment to search symptoms online. Doctor Samui’s 24/7 hotel and villa visit service means you can have a doctor at your room within the hour. You do not have to get in a taxi feeling unwell.

When to Call a Doctor Immediately

Seek medical care the same day if any of the following apply. You have had diarrhea for more than 24 hours and cannot keep fluids down. You have a fever above 38°C. There is blood or mucus in your stool. You feel dizzy, lightheaded, or you are not urinating. You are in your third trimester with cramping alongside diarrhea.

If you are vomiting as well as having diarrhea, you can dehydrate very quickly in Samui’s heat. IV rehydration is safe in pregnancy and is used regularly for this exact situation, both at our Chaweng clinic and during hotel and villa visits across the island.

Do not wait to see if it passes on its own when you are pregnant. Getting checked is always the right call.

What to Expect at the Clinic

When a pregnant patient comes in with diarrhea, we start by assessing hydration. We check blood pressure, pulse, and urine output. If there is any sign of bacterial infection or fever, we run a stool test and blood work.

For diarrhea treatment at Doctor Samui, we carry pregnancy-safe options and will not prescribe anything with a known pregnancy risk without discussing it with you first. If dehydration is moderate or you cannot keep fluids down, IV fluids are the fastest way to get you back on track. This takes around an hour and makes a real difference quickly. We can also run this at your hotel or villa if you would rather not travel while unwell.

Is it safe to take Imodium (loperamide) for diarrhea during pregnancy?

Loperamide is widely available at Thai pharmacies and often recommended without checking for pregnancy first. Its safety in the first trimester is not fully established, and most guidelines advise against using it in pregnancy without medical advice. See a doctor first so you can get a pregnancy-safe option instead.

Can diarrhea during pregnancy cause miscarriage or early labor?

Short-term diarrhea on its own does not directly cause miscarriage. The real risk is severe dehydration and electrolyte loss, which places stress on the pregnancy and can in some cases trigger contractions. In the third trimester, diarrhea combined with cramping or pelvic pressure may signal early labor and needs urgent assessment.

What should I eat and drink if I have diarrhea while pregnant on Koh Samui?

Start with oral rehydration salts mixed with sealed bottled water, available at any 7-Eleven on the island. Eat plain rice, ripe banana, or plain toast and avoid spicy food, dairy, and street ice until you feel better. If you cannot keep fluids down at all, IV rehydration at the clinic or your hotel is the next step.

How do I know if third-trimester diarrhea is a sign of labor starting?

Loose stools alone in late pregnancy are common and not always a labor sign. If diarrhea comes with regular cramping, pelvic pressure, back pain, increased discharge, or fluid leaking, that combination needs urgent review. Doctor Samui can send a doctor to your hotel or villa around the clock so you do not have to travel while this is being sorted.

Is it safe for pregnant women to eat Thai street food and seafood on Koh Samui?

Freshly cooked, hot food from busy vendors is generally lower risk. Avoid raw shellfish entirely during pregnancy, skip buffet food that has been sitting out, and do not eat pre-cut fruit left in the sun. Pregnancy adjusts your immune response, so foodborne illness that a non-pregnant traveler shakes off quickly can hit harder when you are expecting.

Can bacterial food poisoning in Thailand affect my baby directly?

Most bacterial gut infections stay within the digestive tract and do not directly affect the baby. Certain bacteria, particularly Salmonella and Listeria, carry a higher risk during pregnancy and can in rare cases cross to the baby. If you have a fever alongside diarrhea after eating raw or high-risk food, get seen the same day rather than waiting it out.