What defines a threatened abortion?

A threatened abortion is characterized specifically by the presence of vaginal bleeding that occurs while the cervical internal os remains closed. This condition implies that the pregnancy may still continue successfully despite the bleeding, as there are no signs of cervical dilation or other indicators suggesting that the pregnancy has ended.

Vaginal bleeding during early pregnancy is relatively common; however, a key factor that distinguishes a threatened abortion from other types of spontaneous abortion is the closed status of the internal cervical os. If the internal os were open or if there were evidence of the passage of tissue, then it would no longer be classified as threatened, but rather as a type of inevitable or complete abortion, depending on other clinical findings.

The other options describe circumstances that indicate different clinical situations. Painful contractions would typically suggest labor or a more advanced process of miscarriage. Partial passage of products of conception indicates an incomplete abortion, where some tissue has passed but not all, and fetal death with no passage of products suggests a missed abortion. None of these conditions fit the criteria for a threatened abortion, where the pregnancy is still in a state of uncertainty but potentially viable.