There are no official guidelines to assist in answering this question. I will search for relevant research papers instead.
From the Research
Day 21 Progesterone Level
- The day 21 progesterone level is used as an indicator of ovulation in various studies 1, 2, 3, 4
- A study on the effect of basal ovarian cysts on clomiphene citrate ovulation induction cycles found that patients with ovarian cysts were less likely to ovulate, as determined by menstrual cycle day 21 progesterone level 1
- A randomized trial comparing two different doses of Letrozole in women with PCOS found no significant difference in day 21 progesterone level between the two groups 2
- A study on the presentation of polycystic ovary syndrome and its management with clomiphene alone and in combination with metformin used day-21 serum progesterone level to detect ovulation 3
- A study on clinical characteristics of patients with an abnormal clomiphene citrate challenge test found that patients with abnormal tests had lower cycle day 21 progesterone levels and decreased pregnancy rates 4
Progesterone Levels and Pregnancy Outcome
- A study on serum progesterone profile across the mid and late luteal phase in artificial cycles found that ongoing pregnancies were associated with higher serum progesterone levels on days ET+4, ET+7, and ET+11 5
- The study suggests that serum progesterone levels during the late luteal phase may be related to the chances of ongoing pregnancy 5
Ovulation Induction and Progesterone Levels
- A study on the effect of clomiphene citrate on pretreatment simple ovarian cysts found that patients with ovarian cysts were less likely to ovulate, as determined by menstrual cycle day 21 progesterone level 1
- A study on the presentation of polycystic ovary syndrome and its management with clomiphene alone and in combination with metformin found that a combination of metformin and clomiphene citrate significantly increased ovulation and conception rates 3