The luteal phase is the second half of your cycle, from ovulation to your period. It should be at least 10-11 days. If it's shorter than that, an embryto won't have enough time to implant. A short luteal phase usually means low progesterone, which means ovulation was weak. This is one of the most common and most overlooked causes of infertility and early miscarriage. You can catch it yourself with BBT charting. If your temperature drops and your period comes before day 10 after ovulation, your luteal phase is too short. The fix is giving your body what it needs for stronger ovulation: eating enough, reducing stress, balancing blood sugar, B6, zinc, magnesium, and sometimes bioidentical progesterone.