What is a luteal phase defect? Learn the symptoms, how it affects fertility, and how to identify it through cycle tracking.
Your luteal phase is the second half of your cycle — from ovulation to your next period. A luteal phase defect occurs when this phase is too short or when progesterone levels during it are too low. It's an underdiagnosed cause of difficulty conceiving and early pregnancy loss.
After ovulation, the empty follicle becomes the corpus luteum and begins producing progesterone. Progesterone prepares the uterine lining for implantation and supports early pregnancy. If fertilisation doesn't occur, the corpus luteum breaks down, progesterone drops, and your period begins.
The luteal phase normally lasts 12–16 days and is one of the most consistent features of your cycle — it typically varies by only 1–2 days between cycles, even when your overall cycle length varies.
| Luteal phase length | Status | Implication |
|---|---|---|
| 12–16 days | Normal | Sufficient time for implantation |
| 10–11 days | Borderline | May be sufficient; worth monitoring |
| Under 10 days | Short / potential defect | Limited implantation window; consult doctor |
BBT charting is the simplest at-home tool for identifying a luteal phase defect. After ovulation, your basal body temperature rises and should stay elevated for 12–16 days. If your temperature consistently drops within 10 days of ovulation, that's a signal worth investigating.
This is one of the reasons BBT charting is more valuable for TTC than simple period tracking — it reveals the second half of your cycle, not just when your period starts.
If BBT charting shows a consistent luteal phase under 10 days, book an appointment with your GP or gynaecologist. Ask for:
Bring your BBT chart. Three cycles of data is ideal. Treatment options, if a defect is confirmed, typically include progesterone supplementation in the luteal phase — which has good success rates for TTC.
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Start tracking →A luteal phase defect (LPD) is a condition where the luteal phase (the time between ovulation and your period) is shorter than 10 days, or where progesterone levels during the luteal phase are insufficient to support implantation and early pregnancy.
BBT charting is the best at-home method. After ovulation, your temperature should stay elevated for 12–16 days. If it consistently stays elevated for fewer than 10 days before dropping, that suggests a short luteal phase. A doctor can confirm with a progesterone blood test (typically done 7 days after ovulation).
Yes. A short luteal phase means the uterine lining begins to break down before an embryo has time to implant. This can cause very early pregnancy loss, often mistaken for a late period. Treatment — typically progesterone supplementation — can address this.
A normal luteal phase is 12–16 days. A luteal phase shorter than 10 days is generally considered potentially deficient, though some doctors use 12 days as the lower limit. The luteal phase length is one of the most consistent features of a cycle — it typically varies by 1–2 days between cycles.