Luteal phase defect and low progesterone: what is evidence-based and what is not

Maybe someone has told you that your progesterone is too low. Or your cycle chart shows a short second half, and you wonder whether that is why it is not working.

The honest answer is uncomfortable. In 2026, the American Society for Reproductive Medicine (ASRM) stated that there is no reliable test for a luteal phase defect, that it has not been proven as an independent cause of infertility or recurrent miscarriage, and that there is no evidence of benefit for progesterone when trying to conceive without fertility treatment.

Progesterone is not useless, though. After IVF or ICSI it is part of standard care, in a frozen embryo transfer in an artificial cycle it replaces the missing corpus luteum, and for bleeding in early pregnancy after earlier miscarriages there are indications of a small benefit.

What the corpus luteum does

After ovulation, the corpus luteum forms in the ovary. It produces progesterone, which transforms the uterine lining in the second half of the cycle (ASRM 2026). Without ovulation, no corpus luteum forms, less progesterone is produced, and the uterine lining may not be transformed sufficiently (S3 guideline on peri- and postmenopause 2026).

The time from ovulation to the period is called the luteal phase, or corpus luteum phase. In studies it is usually counted from the peak of luteinizing hormone (LH) until the period, and the exact way of counting differs (Lenton 1984, Crawford 2017, ASRM 2026). Progesterone is usually highest 6 to 8 days after ovulation. According to the ASRM, a value above 3 ng/ml points to ovulation having occurred recently.

What is a luteal phase defect?

Specialists speak of luteal insufficiency, or luteal phase deficiency (LPD). The suspected mechanisms are progesterone production that is too brief or too low, or a weak response of the uterine lining to the hormone.

The ASRM defines it as a clinical diagnosis with a luteal phase of 10 days or less, while other definitions use 11 or 9 days. The joint guideline from Germany, Austria, and Switzerland (DACH) on recurrent miscarriage sees it the same way and stresses that there is no progesterone threshold in the blood that defines the diagnosis (AWMF 015-050, version 2.0, May 2026). According to the ASRM, no test reliably distinguishes between fertile women and women with infertility either.

There is also no recognized laboratory definition for “progesterone deficiency.” In prescribing information, the term appears as an indication, for example “progesterone deficiency states” for the active ingredient dydrogesterone. That is approval wording, not evidence of more pregnancies.

How long is a normal luteal phase?

According to the ASRM, the second half of the cycle typically lasts 12 to 14 days, and 11 to 17 days is normal. How much cycle length varies depends mainly on the first half of the cycle (Fehring 2006, 141 women, 1,060 cycles).

A short luteal phase therefore also occurs in healthy women. In the BioCycle study, it occurred repeatedly in only 3.4% of women.

Data box: Short luteal phase and pregnancy

In a US study of 284 women who were trying to get pregnant, the chance of conceiving in the cycle after one with a short luteal phase was somewhat lower (odds ratio 0.82). After 6 months, these women's fertility was significantly lower; after 12 months, there was no longer a significant difference (Crawford 2017). Short here meant 11 days or less, counting the day of ovulation.

Measuring progesterone: timing, values, limits

A progesterone value is only informative in the second half of the cycle. NICE names day 21 of a 28-day cycle, later for longer cycles, for example day 28 of a 35-day cycle, repeated weekly if needed (NICE NG257, 1.18.7 and 1.18.8). The BioCycle team advises measuring about 6 to 8 days after ovulation. A single low value can have various causes: no ovulation in this cycle, an unfavorable time of measurement, normal variation, or a short luteal phase.

What values studies report

The numbers below come from studies and guidelines. They are not normal values for your own results: Labs have their own reference ranges, and after stimulation with clomiphene or gonadotropins, values are higher because several corpora lutea contribute (Hull 1982). 1 ng/ml corresponds to about 3.18 nmol/l.

No study has firmly established a minimum value that is needed for a pregnancy (ESHRE 2023). On top of that, progesterone is released in pulses. According to the ASRM, with normal ovulation, values fluctuate within a short time between 5 and 40 ng/ml and can change by up to eightfold in 90 minutes. In measurements every 10 minutes over 24 hours, they ranged from 2.3 to 40.1 ng/ml in the mid and late luteal phase, often within minutes (Filicori 1984; progesterone measured in 6 women, 4 of them in this phase of the cycle). A single value is therefore hard to interpret.

Measuring with a regular cycle? The guidelines disagree

NICE offers the measurement even with a regular cycle (recommendation from 2004, amended 2013). ESHRE suggests not measuring routinely in that case (2023, conditional recommendation), and the DACH guideline on recurrent miscarriage advises against routine progesterone monitoring with a regular cycle (AWMF 015-050, 2026). According to the international PCOS guideline, disturbed ovulation can also occur with a regular cycle and can then be checked with progesterone (2023). In recurrent miscarriage, ESHRE explicitly advises against testing for a luteal phase defect (2022, strong recommendation).

A tissue sample of the uterine lining does not help either: In a US study with 619 samples evaluated, the lining was out of phase about as often in women from fertile couples as in women with infertility (mid-luteal 49.4% versus 43.2%; Coutifaris 2004). The ASRM advises against it, and molecular tests are considered experimental. In a study cited by ESHRE, a saliva test for progesterone could not detect a luteal phase defect (ESHRE 2022).

Basal body temperature and LH tests

To confirm ovulation, the temperature chart is unreliable, and NICE advises against it (NICE NG257, 1.18.9). In 101 women trying to conceive, it matched the ultrasound in only 74% of cases, while a urine LH test matched in 98 of 101 cases (Guermandi 2001). For the length of the second half of the cycle, however, a chart or LH tests can help: According to the ASRM, they can support normal ovulation and a sufficiently long luteal phase. Our Ovulation Calculator estimates the fertile days based on the calendar; it is a planning aid and does not confirm ovulation. How to measure and read the chart correctly is covered in the guide Measuring basal body temperature, and how LH tests work in the guide Ovulation test.

Symptoms: what is often mentioned and what is evidence-based

Causes: what is associated with a short luteal phase

The ASRM lists conditions that were associated with a luteal phase defect in studies: absence of the period due to a disorder in the diencephalon (hypothalamic amenorrhea), eating disorders, very heavy exercise, marked weight loss, stress, obesity, PCOS, endometriosis, older age, thyroid disorders, elevated prolactin, an unrecognized or inadequately treated 21-hydroxylase deficiency (a disorder of the adrenal gland), as well as hormone stimulation and assisted reproduction. The studies define luteal phase defect differently, and there is no ranking. If such a disorder is present, it is treated first, according to the ASRM.

Prolactin and thyroid: Women with elevated prolactin had shorter luteal phases and lower progesterone (ASRM 2026). NICE calls for a prolactin test in cases of ovulation disorders, milky discharge from the breast, or suspected pituitary tumor, and thyroid levels when there are signs of a thyroid disease (1.18.11 and 1.18.12). Practice in German-speaking countries may differ.

Exercise and energy deficiency: Among 24 recreational women runners with regular cycles, only 45% of cycles were normal, 43% showed a luteal phase defect, and 12% showed no ovulation. Among 11 women who were not athletic, 90% of cycles were normal (De Souza 1998, hormone measurement in urine). A regular cycle therefore does not rule out a short luteal phase.

PCOS, now PMOS: Since May 2026, polycystic ovary syndrome has been called polyendocrine metabolic ovarian syndrome (PMOS) internationally, with a transition period for both names (Lancet 2026). According to the WHO, it is the most common cause of absent ovulation, and treatment then starts there: Getting pregnant with PCOS.

Other factors: In obesity, studies found weaker LH pulses, and in later fertile years less progesterone in the second half of the cycle. A reduced ovarian reserve alone was not associated with a luteal phase defect after accounting for age (ASRM 2026). More smokers were found among women with a short luteal phase (Crawford 2017). On endometriosis: Endometriosis and fertility.

Does progesterone help in a natural cycle?

If no underlying condition is found, treatment is “empiric” according to the ASRM, that is, based on suspicion, and is generally not recommended. There is not a single randomized trial of progesterone for a luteal phase defect, and a benefit in the natural cycle without fertility treatment has not been shown. According to the ASRM, it has likewise not been shown that medications to induce ovulation treat a luteal phase defect. A Cochrane review found no study of progesterone in the natural cycle with sexual intercourse or insemination (Salang 2022).

For women with recurrent miscarriage, however, a second ASRM statement (2026) lists progesterone in the second half of the cycle as possibly useful, with limited or conflicting evidence. The two statements therefore assess this differently.

In Germany, a product with oral micronized progesterone is nevertheless approved for cycle disorders due to progesterone deficiency, and according to the prescribing information also for luteal insufficiency in women with reduced fertility. Another oral product is approved only for menopausal hormone therapy. Dydrogesterone is approved for cycle irregularities due to progesterone deficiency, but not for pregnancy. An approval does not prove a benefit for pregnancies. All medicines containing progesterone or dydrogesterone are prescription-only in Germany (Prescription Drug Ordinance, Arzneimittelverschreibungsverordnung, AMVV); we have not checked Austria and Switzerland.

Instead of treatment based on suspicion, the search for treatable causes comes first. What the workup of both partners involves is explained in the infertility guide.

Progesterone after insemination

After an intrauterine insemination (IUI), the situation is uncertain. In the Cochrane review of women with infertility who wanted to get pregnant by insemination or sexual intercourse after stimulation (25 studies, 5,111 participants), the rate of live births or ongoing pregnancies with vaginal progesterone was not clearly higher (RR 1.10; 95% CI 0.81 to 1.48; 7 studies, 1,792 women; low certainty). After gonadotropin injections, the relative risk was 1.24 (0.80 to 1.92; 4 studies), and after tablets such as clomiphene or letrozole it was 0.97 (0.58 to 1.64; 2 studies; Salang 2022). Another meta-analysis found more live births after gonadotropins (RR 1.41; 1.17 to 1.71; 7 studies, 1,114 women; low to moderate quality; Casarramona 2022).

The approved vaginal and subcutaneous products are indicated for assisted reproduction. Whether insemination falls under that is not clear-cut: According to the international ICMART glossary (2017), it does not, because the eggs are not handled outside the body. The guideline of the German Medical Association on assisted reproduction (2018), by contrast, explicitly includes it. Ask your doctor's office about the approval status. Clomiphene is approved to induce ovulation and letrozole only for breast cancer, so when trying to conceive it is off-label. Both are prescription-only. More: IUI treatment.

Luteal phase support in IVF and ICSI

After hormone stimulation and assisted reproduction, the luteal phase is disrupted (ASRM 2026). That is why you receive progesterone after egg retrieval. ESHRE strongly recommends this but rates the quality of evidence as very low (ovarian stimulation guideline, update 2025). In the Cochrane review, there were more live births or ongoing pregnancies with progesterone than without (odds ratio 1.77; 1.09 to 2.86; 5 studies, 642 women; very low quality; van der Linden 2015).

According to ESHRE, any non-oral route can be used, that is, vaginal capsule, vaginal tablet, gel, or injection. The start is between the evening of egg retrieval and the third day afterward, and the duration is at least until the pregnancy test. With a pregnancy, the German prescribing information specifies, depending on the product, continuing until weeks 7 to 12. The injection under the skin is approved for women who cannot use vaginal products or do not tolerate them.

If ovulation was triggered with hCG, ESHRE advises against hCG for support at the usual dose of 1,500 IU (strong recommendation). In the Cochrane review, hCG clearly increased the risk of overstimulation (ovarian hyperstimulation syndrome, OHSS) compared with placebo (odds ratio 4.28; 1 study). ESHRE tends to advise against additional estradiol. It conditionally recommends dydrogesterone as a tablet, with moderate quality of evidence. In the LOTUS I study, which was funded by the manufacturer, it was not inferior to vaginal progesterone (ongoing pregnancy at week 12: 37.6% versus 33.1%, 974 women with transfer). ESHRE mentions reports of an association with malformations that do not allow any conclusion about a cause. In Germany, dydrogesterone is not approved for pregnancy, so after IVF it is off-label.

After a fresh embryo transfer, the live birth rate with earlier discontinuation was similar in a meta-analysis (RR 0.94; 0.88 to 1.00; 3 studies, 830 women), but a small disadvantage cannot be ruled out (Watters 2020). Decide this only together with your clinic. How soon after transfer you can test is shown by the IVF Due Date Calculator, and the treatment process is described in the article IVF process.

Progesterone in a frozen embryo transfer

In an artificial cycle, no ovulation takes place, no corpus luteum forms, and progesterone replaces it (von Versen-Hoynck 2019). In observational studies, the natural cycle was associated with less preeclampsia (odds ratio 0.50; 30 studies, over 113,000 singleton pregnancies; Zaat 2023). Whether the missing corpus luteum is the cause has not been proven.

In a true natural cycle without a trigger shot, vaginal progesterone raised the live birth rate per woman from 24.1% to 34.2% (Wånggren 2022; 500 women randomized, no placebo, partly funded by the manufacturer). A meta-analysis that combines this study and one other reached the same result (RR 1.43; 1.16 to 1.78; 2 studies, 923 cycles; moderate certainty), but not for the modified natural cycle with an hCG trigger shot (RR 1.04; 0.82 to 1.32; 2 studies, 667 cycles; Erden 2026). More on the cycle types: Frozen embryo transfer.

Progesterone and miscarriage

After a miscarriage, the wish to be able to do something next time is strong. What progesterone can do depends on whether there is bleeding in the new pregnancy.

That a luteal phase defect causes recurrent miscarriage has not been shown (ASRM 2026). In a study cited by ESHRE of 197 women after two miscarriages, a further miscarriage was actually somewhat more common without a luteal phase defect than with one (20.5% versus 15.2%; Ogasawara 1997).

Without bleeding: The PROMISE trial studied 836 women aged 18 to 39 with three or more unexplained early miscarriages. With vaginal progesterone from the positive test until week 12, 65.8% had a live birth, compared with 63.3% with placebo, which is no significant difference (Coomarasamy 2015). The 2025 Cochrane review (women with two or more unexplained miscarriages, without bleeding, without IVF pregnancies) sees probably little or no effect (live birth RR 1.04; 0.96 to 1.12; 5 studies, 1,063 women; moderate certainty).

With bleeding: The PRISM trial included 4,153 women with bleeding in early pregnancy. Overall, 75% with progesterone and 72% with placebo ended with a live birth from week 34 of pregnancy onward, which was narrowly not significant (P = 0.08; Coomarasamy 2019). With at least one earlier miscarriage it was 75% versus 70%, and with three or more it was 72% versus 57% (Coomarasamy 2020). The subgroup with three or more miscarriages was planned in advance but small (285 women), while the subgroup with at least one was formed after the fact. The ASRM regards the subgroups as uncertain because multiple comparisons were made without statistical correction. Cochrane sees a possible benefit for women with an earlier miscarriage and bleeding (RR 1.08; 1.02 to 1.15; subgroup of the studies on vaginal progesterone for bleeding; Devall 2021).

The guidelines do not agree, especially without bleeding:

In Germany, none of the prescribing information reviewed lists miscarriage as an indication, so use here is off-label. Discuss with your gynecologist whether progesterone is an option for you. You should have bleeding in early pregnancy checked by a doctor.

Sometimes progesterone is measured in early pregnancy. The ASRM sees no evidence for measuring it in pregnancies without fertility treatment and supplementing based on the value (2026). In a meta-analysis of spontaneous pregnancies under 14 weeks with pain or bleeding and an unclear ultrasound, a value under 3.2 to 6 ng/ml pointed with high certainty to a pregnancy that was not viable (subgroup of 5 studies with 1,998 women in a meta-analysis of 26 studies; Verhaegen 2012). That does not apply when progesterone is being given, for example after IVF. Only your doctor can put a single value in context.

What can come next after a loss: Pregnant after miscarriage. If the test was only briefly positive: Chemical pregnancy.

Chasteberry and wild yam

The evidence for chasteberry (Vitex agnus-castus) is thin. A small study with 37 evaluated women with a luteal phase defect and slightly elevated prolactin found normalized luteal phases and better progesterone values (Milewicz 1993). Three small studies tested combination products: Two homeopathic products showed no significant benefit (Gerhard 1998, 96 women; Bergmann 2000, 67 women), and for the third, a dietary supplement with many ingredients, the effect cannot be attributed to chasteberry (Westphal 2006, 93 women). There are no robust data for more pregnancies or live births. The European Medicines Agency (EMA) lists chasteberry only for premenstrual syndrome and mild symptoms before the period (2018). Cycle disturbances have been described as a side effect, and it should not be taken during pregnancy (Daniele 2005).

Wild yam cream did not change progesterone levels in a study of 23 postmenopausal women (Komesaroff 2001).

Low progesterone during menopause

A large share of searches about low progesterone concerns menopause, a different topic. In perimenopause, ovulations become less frequent, and in the last year before the final period their rate falls to 5%. No ovulation means no corpus luteum, and therefore less progesterone. Hormone values are meaningful in this phase for only 2 to 4 weeks (S3 guideline on peri- and postmenopause 2026). Oral progesterone is approved there as an addition to estrogen therapy, and it is prescription-only. Whether and how to treat is something you discuss with your gynecologist.

What you can do now

If you suspect a short luteal phase, use LH tests for a few cycles to record when ovulation happened and when your period arrives. According to the ASRM, LH tests and the length of the second half of the cycle recorded this way can support normal ovulation and a sufficiently long luteal phase. A single progesterone value, by contrast, is hard to interpret (ASRM 2026). When a workup of both partners makes sense is explained in the infertility guide. You can find clinics near you in the clinic directory, and guidance on your next step in the Fertility Clinic Finder.

Frequently asked questions

What is a luteal phase defect?

A second half of the cycle (luteal phase) of 10 days or less. The suspected mechanisms are progesterone production that is too brief or too low, or a weak response of the uterine lining. It is a clinical diagnosis, and no laboratory value that defines it exists (ASRM 2026, AWMF 015-050).

What symptoms does a luteal phase defect have?

Only the core feature is evidence-based, a short second half of the cycle. Spotting before the period is often mentioned, but in a small, old study it was more closely linked to endometriosis. That PMS, breast tenderness, or low moods point to progesterone deficiency has not been shown (ASRM 2026, Wentz 1980, Schmidt 1998).

How long is a normal luteal phase?

Usually 12 to 14 days, and 11 to 17 days is normal. In an app data analysis of over 600,000 cycles funded by the provider, the mean was 12.4 days (ASRM 2026, Bull 2019).

When should you measure progesterone?

About 6 to 8 days after ovulation. “Day 21” only fits a 28-day cycle. With a regular cycle, ESHRE tends to advise against routine measurement, as does the DACH guideline on recurrent miscarriage, while NICE offers it (ASRM 2026, Schliep 2014, NICE NG257, ESHRE 2023, AWMF 015-050).

Can you get pregnant with a luteal phase defect?

Yes. After a cycle with a short second half, the chance in the next cycle was somewhat lower, and after 12 months there was no significant difference (Crawford 2017, 284 women).

Does progesterone help when trying to conceive without fertility treatment?

There is no randomized trial and no evidence of benefit. A product is approved in Germany for cycle disorders due to progesterone deficiency, but that does not show an advantage for pregnancies (ASRM 2026, Cochrane 2022).

How long do I have to take progesterone after a fresh transfer?

At least until the pregnancy test, and with a pregnancy, depending on the product, until weeks 7 to 12. Stopping earlier after a fresh transfer gave similar results in a meta-analysis, though a small disadvantage cannot be ruled out. Decide this only together with your clinic (ESHRE 2025, Watters 2020).

Does progesterone prevent a miscarriage?

Probably not without bleeding in unexplained recurrent miscarriage (PROMISE: 65.8% versus 63.3% live births). With bleeding and an earlier miscarriage, vaginal progesterone may possibly help (75% versus 70% in a subgroup of PRISM formed after the fact; Cochrane: possible benefit). The guidelines do not agree, and in Germany use is off-label (Coomarasamy 2015, 2019, and 2020; Cochrane 2025; NICE NG126).

Can I buy progesterone over the counter?

No. Medicines containing progesterone or dydrogesterone are prescription-only in Germany. Wild yam cream did not raise progesterone levels in a study of 23 postmenopausal women (AMVV Annex 1, Komesaroff 2001).

Sources

Guidelines and position statements

• Practice Committees of ASRM and SREI: Diagnosis and treatment of luteal phase deficiency: a Committee Opinion, Fertil Steril 2026;126(4):633-639, ASRM, July 2026
• Practice Committee of ASRM: Recurrent pregnancy loss: a committee opinion, Fertil Steril 2026;125:1023-1041, ASRM, 2026
• ESHRE Guideline Ovarian Stimulation for IVF/ICSI, Update 2025, Hum Reprod 2026;41(4):498-514, ESHRE, 2025
• ESHRE Guideline Group on RPL: Recurrent pregnancy loss, an update in 2022, Hum Reprod Open 2023;hoad002, ESHRE
• ESHRE Guideline Recurrent Pregnancy Loss, Update 2022, full text with evidence chapters, ESHRE, January 2023
• Romualdi D et al.: Evidence-based guideline: unexplained infertility, Hum Reprod 2023;38(10):1881-1890, ESHRE, 2023
• NICE NG257: Investigation of fertility problems and management strategies, recommendations 1.18.7 to 1.18.12, NICE, March 31, 2026
• NICE NG126: Ectopic pregnancy and miscarriage, recommendations 1.9.2 and 1.9.3, NICE, last updated June 17, 2026
• DGGG, OEGGG, SGGG: S2k guideline on diagnosis and treatment of women with recurrent miscarriage, AWMF 015-050, version 2.0, as of May 2026
• S3 guideline on peri- and postmenopause: diagnosis and interventions, AWMF 015-062, long version, file version June 2026
• Teede HJ et al.: Recommendations from the 2023 International Evidence-based Guideline for the Assessment and Management of PCOS, J Clin Endocrinol Metab 2023;108(10):2447-2469
• Teede HJ et al.: Polyendocrine metabolic ovarian syndrome, the new name for polycystic ovary syndrome, Lancet 2026;407(10545):2329-2339
• Polycystic ovary syndrome, Fact Sheet, WHO, January 22, 2026
• Zegers-Hochschild F et al.: The International Glossary on Infertility and Fertility Care, 2017, Hum Reprod 2017, ICMART
• German Medical Association: Guideline on the retrieval and transfer of human germ cells in assisted reproduction, sections 1.2 and 1.4, Federal Gazette (BAnz AT) of July 20, 2018, B3, Paul-Ehrlich-Institut
• Agni casti fructus, monograph, revision 1, EMA/HMPC, October 10, 2018

Cochrane reviews and meta-analyses

• Haas DM et al.: Progestogen for preventing miscarriage in women with recurrent miscarriage of unclear etiology, Cochrane Database Syst Rev 2025, CD003511.pub6
• Devall AJ et al.: Progestogens for preventing miscarriage: a network meta-analysis, Cochrane Database Syst Rev 2021, CD013792.pub2
• Salang L et al.: Luteal phase support for women trying to conceive by intrauterine insemination or sexual intercourse, Cochrane Database Syst Rev 2022, CD012396.pub2
• van der Linden M et al.: Luteal phase support for assisted reproduction cycles, Cochrane Database Syst Rev 2015, CD009154.pub3
• Ford O et al.: Progesterone for premenstrual syndrome, Cochrane Database Syst Rev 2012, CD003415.pub4
• Casarramona G et al.: The efficacy and safety of luteal phase support with progesterone following ovarian stimulation and intrauterine insemination: a systematic review and meta-analysis, Front Endocrinol 2022;13:960393
• Watters M et al.: Short versus extended progesterone supplementation for luteal phase support in fresh IVF cycles: a systematic review and meta-analysis, Reprod Biomed Online 2020;40(1):143-150
• Erden M et al.: Revisiting natural cycle frozen embryo transfer: a systematic review and meta-analysis, Hum Reprod Update 2026;32(4):439-457
• Zaat TR et al.: Obstetric and neonatal outcomes after natural versus artificial cycle frozen embryo transfer and the role of luteal phase support, Hum Reprod Update 2023;29(5):634-654
• Verhaegen J et al.: Accuracy of single progesterone test to predict early pregnancy outcome in women with pain or bleeding: meta-analysis of cohort studies, BMJ 2012;345:e6077

Studies

• Lenton EA et al.: Normal variation in the length of the luteal phase of the menstrual cycle: identification of the short luteal phase, Br J Obstet Gynaecol 1984;91(7):685-689
• Bull JR et al.: Real-world menstrual cycle characteristics of more than 600,000 menstrual cycles, NPJ Digit Med 2019;2:83, funded by the app provider
• Crawford NM et al.: Prospective evaluation of luteal phase length and natural fertility, Fertil Steril 2017;107(3):749-755
• Schliep KC et al.: Luteal phase deficiency in regularly menstruating women (BioCycle), J Clin Endocrinol Metab 2014;99(6):E1007-1014
• Fehring RJ et al.: Variability in the phases of the menstrual cycle, J Obstet Gynecol Neonatal Nurs 2006;35(3):376-384
• Hull MG et al.: The value of a single serum progesterone measurement in the midluteal phase as a criterion of a potentially fertile cycle, Fertil Steril 1982;37(3):355-360
• Filicori M et al.: Neuroendocrine regulation of the corpus luteum in the human. Evidence for pulsatile progesterone secretion, J Clin Invest 1984;73(6):1638-1647
• Guermandi E et al.: Reliability of ovulation tests in infertile women, Obstet Gynecol 2001;97(1):92-96
• Coutifaris C et al.: Histological dating of timed endometrial biopsy tissue is not related to fertility status, Fertil Steril 2004;82(5):1264-1272
• Wentz AC: Premenstrual spotting: its association with endometriosis but not luteal phase inadequacy, Fertil Steril 1980;33(6):605-607
• Schmidt PJ et al.: Differential behavioral effects of gonadal steroids in women with and in those without premenstrual syndrome, N Engl J Med 1998;338(4):209-216
• De Souza MJ et al.: High frequency of luteal phase deficiency and anovulation in recreational women runners, J Clin Endocrinol Metab 1998;83(12):4220-4232
• Coomarasamy A et al.: A randomized trial of progesterone in women with recurrent miscarriages (PROMISE), N Engl J Med 2015;373(22):2141-2148
• Coomarasamy A et al.: A randomized trial of progesterone in women with bleeding in early pregnancy (PRISM), N Engl J Med 2019;380:1815-1824
• Coomarasamy A et al.: Micronized vaginal progesterone to prevent miscarriage: a critical evaluation of randomized evidence, Am J Obstet Gynecol 2020;223(2):167-176
• Tournaye H et al.: Oral dydrogesterone versus micronized vaginal progesterone for luteal support in in vitro fertilization (LOTUS I), Hum Reprod 2017;32(5):1019-1027, funded by the manufacturer
• Wånggren K et al.: Progesterone supplementation in natural cycles improves live birth rates after embryo transfer of frozen-thawed embryos: a randomized controlled trial, Hum Reprod 2022;37(10):2366-2374
• von Versen-Hoynck F et al.: Increased preeclampsia risk and reduced aortic compliance with in vitro fertilization cycles in the absence of a corpus luteum, Hypertension 2019;73(3):640-649
• Milewicz A et al.: Vitex agnus castus extract in the treatment of luteal phase defects due to latent hyperprolactinemia, randomized placebo-controlled double-blind trial, Arzneimittelforschung 1993;43(7):752-756
• Gerhard I et al.: Study of a homeopathic combination product with chasteberry in female infertility, Forsch Komplementarmed 1998;5(6):272-278 (original title includes brand names)
• Bergmann J et al.: Study of a homeopathic combination product in hormonally caused infertility, Forsch Komplementarmed Klass Naturheilkd 2000;7(4):190-199 (original title includes brand names)
• Westphal LM et al.: Double-blind, placebo-controlled study of a nutritional supplement for improving fertility in women, Clin Exp Obstet Gynecol 2006;33(4):205-208 (original title includes brand names)
• Daniele C et al.: Vitex agnus castus: a systematic review of adverse events, Drug Saf 2005;28(4):319-332
• Komesaroff PA et al.: Effects of wild yam extract on menopausal symptoms, lipids and sex hormones in healthy menopausal women, Climacteric 2001;4:144-150

Approval and law in Germany

• Prescribing information for progesterone 100 mg and 200 mg oral soft capsules, as of January 2023
• Prescribing information for progesterone 100 mg oral soft capsules, indication endometrial protection, as of May 2022
• Prescribing information for progesterone 200 mg soft capsules for vaginal use, as of February 2026
• Prescribing information for progesterone vaginal gel 90 mg, as of February 2022
• Prescribing information for progesterone 25 mg solution for injection, as of November 2023
• Prescribing information for dydrogesterone 10 mg film-coated tablets, as of September 2025
• Prescribing information for clomiphene 50 mg tablets, as of August 2016
• Prescribing information for letrozole 2.5 mg film-coated tablets, as of April 2025
• Prescription Drug Ordinance (Arzneimittelverschreibungsverordnung, AMVV), Annex 1, Federal Ministry of Justice (Bundesministerium der Justiz), accessed October 4, 2026