After an embryo transfer, most people are told to take progesterone for a number of days or weeks. It can feel like a small detail compared with stimulation injections or the transfer itself, yet it is one of the most routine parts of IVF care. This article explains what luteal phase support is, why it is used, how it differs between fresh and frozen cycles, and where the evidence is firm and where it is still uncertain.
What is the luteal phase?
In a natural menstrual cycle, the luteal phase is the time between ovulation and either the next period or the start of a pregnancy. After the egg is released, the follicle that held it changes into a structure called the corpus luteum. The corpus luteum produces progesterone, a hormone that converts the uterine lining (the endometrium) from a growing, proliferative state into a receptive, supportive one. Progesterone also helps maintain the early pregnancy until the placenta takes over hormone production.
In simple terms, progesterone is the hormone that prepares the lining to accept and nourish an embryo. If the lining and the embryo are not developmentally in step with each other, implantation may be less likely to proceed.
Why the luteal phase needs help in IVF
Ovarian stimulation changes the usual hormonal pattern. A review of luteal support practice published in Frontiers in Endocrinology in 2020 describes the luteal phase as deficient in almost all patients who undergo ovarian stimulation for IVF, and links this to altered endometrial development that can leave the lining out of step with the embryo. The same review attributes the problem to ovarian stimulation in general and does not claim a single proven mechanism.
Because of this, luteal phase support (often abbreviated LPS) is a standard part of IVF and ICSI. It simply means giving the body the hormone, usually progesterone, that the stimulated ovaries may not supply adequately after egg collection.
Progesterone: the cornerstone of luteal support
The European Society of Human Reproduction and Embryology (ESHRE) guideline on ovarian stimulation, published in 2019, makes a strong recommendation that progesterone be used for luteal phase support after IVF or ICSI. This is one of the firmest recommendations in this area.
The same guideline gives practical points that clinics commonly follow:
Timing: progesterone is started between the evening of egg collection and the third day after collection. Starting before egg collection is discouraged.
Duration: it is continued at least until the pregnancy test.
Route: any non-oral route of natural progesterone can be used. The guideline lists examples including intramuscular injection, subcutaneous injection, vaginal gel, and several vaginal capsule, tablet or pessary forms.
Oral natural progesterone is generally not used because it is broken down rapidly by the body, whereas vaginal, subcutaneous and intramuscular forms reach higher levels.
Which route is better?
Patients often ask whether injections work better than vaginal inserts. A Cochrane review of luteal phase support in assisted reproduction (van der Linden and colleagues, 2015), which pooled 94 randomised trials, found no clear differences in outcomes between intramuscular, oral, vaginal and rectal progesterone, nor between lower and higher vaginal doses. ESHRE reached a similar conclusion, noting no major differences in effectiveness between non-oral routes.
In practice, the choice often comes down to tolerability and convenience. Vaginal products can cause discharge or irritation; injections can cause soreness at the injection site. Your clinic will choose a regimen based on your cycle type, your history and its own protocols. If a particular form is not tolerable, it is worth telling the team so an alternative can be considered rather than stopping the medication on your own.
How strong is the evidence for progesterone?
It is fair to be transparent about the quality of the evidence. In the Cochrane review, trials comparing progesterone with placebo or no treatment were small and rated as very low quality. One statistical approach suggested a higher live birth or ongoing pregnancy rate with progesterone, while another approach did not show a clear difference. The guideline recommendation therefore rests on this body of evidence together with the biological rationale for correcting luteal deficiency after stimulation.
Other medicines that have been used
hCG
Human chorionic gonadotropin (hCG) can stimulate the corpus luteum to make its own progesterone. Studies comparing hCG with progesterone found no clear difference in live birth or ongoing pregnancy, but hCG for luteal support was associated with a higher risk of ovarian hyperstimulation syndrome (OHSS), a potentially serious over-response of the ovaries. For this reason, the ESHRE guideline conditionally advises against routine standard-dose hCG for luteal support, particularly in women who respond strongly to stimulation.
Oestradiol
Many clinics have historically added oestradiol alongside progesterone. The Cochrane review found no clear benefit from doing so, and ESHRE conditionally recommends against routine oestradiol addition for luteal support, since it has not been shown to improve live birth or ongoing pregnancy rates or reduce OHSS.
Dydrogesterone
Dydrogesterone is an oral progestogen with a different chemical structure from natural progesterone. ESHRE conditionally supports its use as an option, noting that ongoing pregnancy rates appear similar to those with progesterone and that many patients prefer an oral route, while also noting that the safety data were considered insufficient for a firm statement. Availability and local practice vary.
GnRH agonist additions
Adding a GnRH agonist injection to progesterone has been studied. The Cochrane review reported an association with higher live birth or ongoing pregnancy rates, but the evidence was of low quality with considerable variation between trials. ESHRE therefore advises that this approach be used only in clinical trials rather than as routine care.
Luteal support in frozen embryo transfer
Frozen embryo transfer (FET) is now a very common part of IVF, and the luteal question looks different here. The answer depends heavily on how the lining is prepared.
In a programmed or hormone replacement FET cycle, the lining is built with oestrogen and then progesterone, without relying on the woman's own ovulation. Without ovulation there is no corpus luteum, so the medication supplies the hormone support for the lining and the early pregnancy. The Frontiers review suggests this may be why extended support is increasingly used in these cycles, while presenting this as a possible explanation rather than a proven one.
In a natural cycle FET, ovulation occurs and a corpus luteum forms, so the need for extra progesterone is less clear. A 2020 meta-analysis in Clinical and Experimental Reproductive Medicine looked at vaginal progesterone in natural-cycle FET. It found no significant difference in clinical pregnancy rates (odds ratio 0.96, 95% confidence interval 0.60 to 1.55), although two retrospective studies suggested a higher live birth rate with progesterone. The analysis included only one randomised trial, and the authors themselves call for more research, particularly in people with recurrent miscarriage or repeated implantation failure. Approaches therefore differ between clinics in natural and modified natural FET cycles.
Does blood progesterone testing help?
Some clinics measure serum progesterone around the time of an FET and add more progesterone when the level seems low. A 2025 single-centre retrospective study in Frontiers in Reproductive Health (433 programmed FET cycles) compared women with progesterone below 11 ng/ml who received additional subcutaneous progesterone with women who had higher levels on standard vaginal treatment. Progesterone levels were similar between the groups by day 12 after transfer, and the live birth rate was higher in the rescue group (36.9 per cent versus 24.7 per cent). The authors point out that the retrospective design cannot prove cause, that timing of blood sampling was not standardised, and that controlled trials are needed. At present this should be seen as an area of active research rather than a settled standard.
How long should luteal support continue?
ESHRE advises continuing progesterone at least until the pregnancy test. What happens after a positive test is less uniform. The Cochrane review found no clear difference between shorter and longer progesterone courses in the trials it analysed. In practice, the length of support after a positive test depends on the cycle type, the clinical findings and the protocol of the treating team, so it is best not to stop or change medication without instruction.
Common questions patients raise
Do side effects show whether the treatment is working?
No. Progesterone can cause breast tenderness, bloating, tiredness, mood changes and mild cramps. These symptoms can occur whether or not a pregnancy follows, so they cannot be used to predict the result of a cycle. Equally, having no symptoms does not suggest a problem.
What if I miss a dose?
Missed or late doses are common and understandably worrying. Contact your fertility team promptly for advice specific to your regimen rather than doubling doses on your own, because different products have different dosing intervals.
Is spotting normal on progesterone?
Light spotting can happen in early pregnancy and during luteal support, but it can also have other causes. Heavier bleeding, severe pain, dizziness, or fever should be reported to your clinic or emergency services without delay.
Does luteal support guarantee a pregnancy?
No. Luteal support is intended to compensate for the hormonal changes of treatment around implantation. It does not guarantee implantation or prevent every early pregnancy loss, and its benefit depends on many other factors including embryo quality and the uterine environment.
Key points to take away
Luteal phase support replaces or supplements the progesterone that the lining needs after egg collection or during a programmed frozen cycle.
Progesterone is the recommended agent after IVF or ICSI, with starting time, duration and route chosen by the clinic. Non-oral routes are generally used, and no clear difference in outcome has been shown between them.
hCG, oestradiol and GnRH agonist add-ons are not routinely recommended, and hCG carries a higher OHSS risk in strong responders.
In natural-cycle FET and in strategies using blood progesterone levels, the evidence is still developing and practice varies between clinics.
Questions about doses, side effects or stopping should be directed to your treating team, because the right plan depends on your cycle type and history.
This article is for general education and does not replace individual medical advice. Outcomes of IVF vary and no luteal support regimen can guarantee implantation or a pregnancy.
References
- ESHRE Reproductive Endocrinology Guideline Group. Ovarian Stimulation for IVF/ICSI: Guideline of the European Society of Human Reproduction and Embryology (Chapter 16, Luteal phase support). ESHRE; 2019. https://www.eshre.eu/-/media/sitecore-files/Guidelines/COS/ESHRE-COS-guideline_final-09102019_.pdf
- van der Linden M, Buckingham K, Farquhar C, Kremer JAM, Metwally M. Luteal phase support for assisted reproduction cycles. Cochrane Database of Systematic Reviews; 2015 (CD009154). https://www.cochrane.org/evidence/CD009154_luteal-phase-support-assisted-reproduction
- Di Guardo F, Midassi H, Racca A, Tournaye H, De Vos M, Blockeel C. Luteal Phase Support in IVF: Comparison Between Evidence-Based Medicine and Real-Life Practices. Frontiers in Endocrinology; 2020;11:500. https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2020.00500/full
- Seol A, Shim YJ, Kim SW, et al. Effect of luteal phase support with vaginal progesterone on pregnancy outcomes in natural frozen embryo transfer cycles: A meta-analysis. Clinical and Experimental Reproductive Medicine; 2020;47(2):147-152. https://doi.org/10.5653/cerm.2019.03132
- Yazbeck C, Olivennes F, Kazdar N, Pietin-Vialle C, Gricourt S. Effect of a luteal phase rescue protocol on live birth rates in frozen embryo transfer cycles. Frontiers in Reproductive Health; 2025;7. https://www.frontiersin.org/articles/10.3389/frph.2025.1547939/full