Zygote Implantation: Probability, Timing, and Influencing Factors

Overall Chance

~30–40% of fertilized eggs implant successfully.

Key Steps

1. Fertilization: ~20–30% of sperm‑egg encounters succeed.
2. Blastocyst Formation: Days 5–6 post‑fertilization.
3. Implantation Window: Days 5–10 after ovulation (endometrium receptive).

Critical Factors

• Endometrial receptivity (progesterone‑dependent)
• Blastocyst quality (genetic normality, morphology)
• Uterine anatomy (fibroids, polyps, adhesions)
• Immune balance (tolerance vs. rejection)
• Age, lifestyle (smoking, alcohol), medical conditions