Gastroenteritis: This is often the most common cause of loose motions in pregnancy, including the first trimester. Viral or bacterial infections can lead to gastroenteritis, which is usually self-limiting but can cause significant discomfort and dehydration.

Food Poisoning: Similar to gastroenteritis, food poisoning from consuming contaminated food or water can cause loose motions. The first trimester does not exempt pregnant individuals from this common issue.
Pregnancy-Related Gastrointestinal Changes: Hormonal changes in early pregnancy can affect bowel habits, leading to loose motions or diarrhea in some cases.
Irritable Bowel Syndrome (IBS): Although not directly caused by pregnancy, IBS can exacerbate during the first trimester due to hormonal changes, leading to episodes of diarrhea.

Hyperemesis Gravidarum: While primarily known for severe nausea and vomiting, hyperemesis gravidarum can also cause loose motions due to the frequent vomiting and potential for gastrointestinal upset.
Listeriosis: A bacterial infection that can cause severe illness, including diarrhea, and is particularly dangerous during pregnancy due to the risk of transmission to the fetus.
Appendicitis: Although less common, appendicitis can present with gastrointestinal symptoms, including diarrhea, and is a medical emergency requiring prompt surgical intervention.

Inflammatory Bowel Disease (IBD) Flare: Conditions like Crohn's disease or ulcerative colitis can cause diarrhea and may flare during pregnancy, although this is less common in the first trimester.
Giardiasis: An intestinal infection caused by the parasite Giardia lamblia, which can lead to chronic diarrhea and is more common in travelers or those exposed to contaminated water.
Thyroid Disorders: Both hyperthyroidism and hypothyroidism can affect bowel habits, but these are less common causes of loose motions in the first trimester compared to other diagnoses listed.