Uterine Implantation Site: Normal Location & Variations

Normal Implantation

The blastocyst typically implants in the posterior wall of the uterine corpus (fundus), in the functional layer of the endometrium, during the window of implantation (days 20–24 of a 28-day cycle, ~6–10 days post-fertilization).

Variations & Clinical Significance

Site	Term	Clinical Relevance
Posterior fundal (most common)	Normal	Optimal placental development, lower previa risk.
Anterior fundal	Normal variant	May delay maternal perception of fetal movement.
Lower uterine segment / Cervical os	Placenta Previa	Painless bleeding; C-section delivery.
Fallopian tube / Ovary / Peritoneum	Ectopic Pregnancy	Rupture risk; medical/surgical emergency.
Cesarean Scar	Cesarean Scar Pregnancy	High risk of hemorrhage, hysterectomy, accreta spectrum.

Imaging Confirmation

• Transvaginal ultrasound: Gestational sac location, yolk sac, fetal pole, cardiac activity.
• MRI for complex cases (scar, interstitial, cervical).