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Inevitable abortion involves vaginal bleeding with an open cervix and often visible products of conception. The cervix in this case is closed, and fetal heart rate is present, ruling out inevitable abortion. Uterine contractions may also be present in inevitable cases.

Incomplete abortion presents with passage of tissue, persistent bleeding, and an open cervix. Ultrasound typically shows retained products. The presence of fetal cardiac activity and absence of tissue passage exclude incomplete abortion.

Missed abortion is characterized by absence of fetal cardiac activity despite retained products and a closed cervix. The patient in this case has a detectable fetal heart rate, excluding missed abortion. Bleeding may be minimal or absent in missed abortion.

Maternal infections such as toxoplasmosis, rubella, cytomegalovirus, and herpes simplex virus can cause miscarriage, but they are more commonly associated with second trimester losses or fetal anomalies. In the first trimester, their contribution is significantly lower. TORCH pathogens and vertical transmission are relevant but not predominant.

Uterine abnormalities like septate uterus, fibroids, or adhesions (Asherman syndrome) can impair implantation or placental development, leading to miscarriage. However, these structural issues typically cause recurrent pregnancy loss or second trimester abortions. Anatomic defects and implantation failure are less common in early loss.

Endocrine disorders such as uncontrolled diabetes mellitus, luteal phase defects, or thyroid dysfunction can contribute to miscarriage, but they are not the leading cause. Their impact is more pronounced in recurrent losses or later gestational failures. Hormonal imbalance and thyroid dysfunction are contributory but not primary.

Placenta previa involves abnormal placental implantation over the cervical os, typically diagnosed via ultrasound in the second or third trimester. It is unrelated to retained products in early pregnancy and does not result from missed abortion. No pathophysiologic link exists between retained fetal tissue and placental migration.

Ectopic pregnancy occurs when implantation happens outside the uterine cavity, most commonly in the fallopian tube. It presents with abdominal pain and vaginal bleeding, often before 8 weeks gestation. Missed abortion implies intrauterine pregnancy loss, not ectopic implantation, making this option pathologically incompatible.

Preterm labor refers to uterine contractions leading to cervical changes before 37 weeks gestation. It is associated with infections, uterine overdistension, or cervical insufficiency. In missed abortion, fetal demise has already occurred, and uterine activity is typically absent unless induced. Retained tissue does not trigger preterm labor mechanisms.