Objective Antenatal vaginal bleeding, particularly during the first trimester, is worrisome for obstetricians. The common causes are all types of abortions, including molar and ectopic pregnancies. The aim is to evaluate the obstetric causes of vaginal bleeding during the first trimester.

Methods The study population comprises 100 pregnant women with complaints of vaginal bleeding during their first trimester period. These patients were subjected to ultrasound examination to diagnose the causes of bleeding. Patients with 12 completed weeks of gestation and non-obstetrical causes of vaginal bleeding were excluded.

Results The study population of 18-34 years had complained of vaginal bleeding during their first trimester of pregnancy. Most 57% were in the age group of 20-24 years. Forty-two percent of the study population presented at ten weeks of amenorrhea. Out of 100 cases, the majority (58%) were diagnosed as threatened abortion, 31% cases were diagnosed as incomplete abortion, 4% cases were diagnosed as complete abortion, 2 (2%) cases each were diagnosed as ectopic gestation, inevitable and missed abortions, and 1 (1%) case diagnosed as Hydatidiform mole. Out of 100 patients, the gestational sac was seen in 75 (75%).

Conclusion Antenatal ultrasonography is helpful in accurate and early diagnosis of the causes of vaginal bleeding during the first trimester. This aids the obstetrician in selecting the best treatment planning and helps with prognosis prediction, establishing an accurate diagnosis in a few clinically misdiagnosed cases.