Explanation

Chlamydial infection, especially if it leads to inflammation or scarring of the fallopian tubes, increases the risk of an ectopic pregnancy.

This is because the scarring or damage to the fallopian tubes can hinder the normal passage of a fertilized egg from the fallopian tube to the uterus

Leading to the implantation of the embryo outside of the uterus

Typically in the fallopian tube (which is characteristic of ectopic pregnancy).

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The other options listed do not directly increase the risk of ectopic pregnancy.