Hormone Test
Progesterone Test
A detailed guide to the Progesterone test, the primary method for confirming ovulation and assessing whether the uterus is ready to support a pregnancy.
Test Overview
Progesterone is known as the "pro-gestation" hormone. It dominates the second half of the cycle (Luteal Phase).
Key Purpose
To answer the question: "Did I ovulate?". If progesterone is low in the second half of your cycle, ovulation likely did not occur.
1. Purpose and Uses of the Progesterone Test
While FSH and LH focus on the quality of the egg and timing of release, Progesterone focuses on what happens after the egg is released.
Common Indications
- Confirming that ovulation has occurred.
- Diagnosing Luteal Phase Defect (when the second half of the cycle is too short or hormonal support is too weak to sustain a pregnancy).
- Monitoring early pregnancy health (to prevent miscarriage).
- Diagnosing ectopic pregnancy or failing pregnancy (alongside hCG tests).
2. The "Day 21" Rule (Timing is Everything)
Progesterone is low during the first half of the cycle. It rises sharply only after ovulation. Therefore, timing the blood draw is critical.
Why "Day 21" Can Be Wrong
Doctors often order a "Day 21 Progesterone" test. This assumes you have a textbook 28-day cycle and ovulate on Day 14.
- The Rule: You should test 7 days after ovulation (the mid-luteal phase).
- If you have a 28-day cycle: Test on Day 21.
- If you have a 35-day cycle: You likely ovulate around Day 21. If you test on Day 21, the result will be low (false negative). You should test on Day 28.
Calculating Your Test Day
Do not strictly follow "Day 21" if your periods are irregular. Use ovulation predictor kits (OPKs) to find your surge, then count 7 days forward to schedule your blood test for the most accurate results.
3. Role in Pregnancy
Once the egg is released, the empty follicle becomes the Corpus Luteum, which pumps out progesterone.
- Uterine Lining: It thickens the endometrium, creating a "sticky" environment for the embryo to implant.
- Muscle Relaxant: It prevents uterine contractions that might reject the embryo.
- Immune Modulation: It signals the mother's immune system not to attack the fetal DNA.
4. Normal Levels
Levels fluctuate wildly depending on where you are in your cycle or pregnancy. Below are general reference ranges (ng/mL):
| Cycle Phase | Range (ng/mL) | Status |
|---|---|---|
| Follicular Phase (Start of cycle) | < 1.0 ng/mL | Pre-ovulation |
| Mid-Luteal Phase (7 days post-ovulation) | 5 – 20 ng/mL | Ovulation Confirmed |
| Post-Menopause | < 1.0 ng/mL | Normal low |
| First Trimester | 11 – 44 ng/mL | Supporting pregnancy |
| Second Trimester | 25 – 83 ng/mL | Placenta taking over |
Note: To convert ng/mL to nmol/L, multiply by 3.18.
5. Interpreting Results
Low Progesterone (Mid-Luteal)
A result below 5 ng/mL (sometimes below 3 ng/mL depending on the lab) 7 days after expected ovulation usually indicates:
- Anovulation: No egg was released.
- Luteal Phase Defect: The corpus luteum is not producing enough hormone to support implantation.
- Timing Error: The test was taken too early or too late relative to ovulation.
High Progesterone
- Pregnancy: Levels remain high instead of dropping at the end of the cycle.
- Multiples: Twins or triplets often produce higher hormone levels.
- Cysts: A luteal cyst may cause persistent elevation.
6. Treatment and Support
Low progesterone is one of the easier fertility issues to manage. It is a standard part of IVF and IUI protocols.
- Vaginal Suppositories: The most common treatment. Progesterone capsules are inserted vaginally to deliver the hormone directly to the uterus.
- Injections: Progesterone in Oil (PIO) injections are frequently used during IVF cycles to ensure absorption.
- Oral Medication: Less common due to side effects (drowsiness) and lower absorption rates compared to vaginal or injectable routes.
If you are prescribed progesterone, you typically continue taking it until the 10th or 12th week of pregnancy, when the placenta matures enough to take over hormone production.