Miscarriage: This is a common cause of abdominal cramps in the first trimester, often accompanied by vaginal bleeding. The cramps can range from mild to severe and are usually a sign of the body expelling the pregnancy.

Implantation Cramping: Mild cramping can occur as the embryo implants into the uterine lining, usually within the first few weeks of pregnancy.
Constipation: Hormonal changes in early pregnancy can lead to constipation, which may cause abdominal cramps.
Urinary Tract Infections (UTIs): Pregnancy increases the risk of UTIs, which can cause abdominal cramps, among other symptoms like dysuria and frequent urination.

Ectopic Pregnancy: Although less common, ectopic pregnancy is a life-threatening condition that requires immediate medical attention. Symptoms include severe abdominal pain, vaginal bleeding, and sometimes shoulder tip pain.
Appendicitis: Appendicitis can occur at any time during pregnancy and may present with abdominal pain, initially diffuse or around the navel, then localizing to the lower right abdomen.
Placenta Previa: While more common in the second and third trimesters, placenta previa can cause painless vaginal bleeding in the first trimester, but it's crucial to consider due to its potential for severe bleeding.

Ovarian Cysts: Ovarian cysts can cause abdominal pain and are more likely to rupture during pregnancy, although they are not as common as other causes of abdominal cramps in the first trimester.
Adnexal Torsion: A rare condition where the ovary or fallopian tube twists, cutting off its blood supply. It's extremely painful and requires emergency surgery.