Oestradiol and progesterone during IVF: how to interpret your blood test results

During IVF, two hormones crop up time and again in the reports: oestradiol, during stimulation, and progesterone, at the time of the trigger injection and before an embryo transfer. Patients often receive the results before they have spoken to their doctor, and try to work out what they mean on their own. Here are some pointers to help you interpret them without getting worried, and the situations where the figure actually changes the course of action.

Two hormones, two roles

• Oestradiol is produced by the follicles growing in the ovaries. During stimulation, its level rises as the follicles develop. It therefore roughly reflects the amount of growing follicular tissue.
• Progesterone prepares the endometrium so that it can receive the embryo. It normally rises after ovulation. Before an embryo transfer, it is this hormone that ‘triggers’ the window during which implantation is possible.

The pitfall of units

The same result can be expressed in two different ways, depending on the laboratory and the country. This is the first thing to check before comparing a figure with a threshold value found elsewhere.

Oestradiol during stimulation

There is no universal ‘ideal’ oestradiol level: it depends on the number and size of the follicles, the day of stimulation and the protocol. This is why ultrasound remains the primary diagnostic tool. The ESHRE guidelines on ovarian stimulation, updated in 2025, also state that the routine addition of an oestradiol test to ultrasound monitoring is probably not recommended.

A ‘low’ oestradiol level may simply correspond to a small number of growing follicles, which indicates a poor response to stimulation. It may also be intentional: some protocols include letrozole, which deliberately lowers oestradiol levels. A very high level, conversely, generally indicates a large number of follicles and is one of the signs that lead the doctor to adjust the trigger treatment or to freeze all the embryos to prevent hyperstimulation. In both cases, it is the overall picture that matters, not an isolated figure.

Progesterone on the day of trigger injection

During stimulation, progesterone levels must remain low. An early rise, before the trigger injection, primarily affects the endometrium: it accelerates its maturation, which may then no longer be in sync with the embryo during a fresh transfer. There is debate regarding its effect on embryo quality, and studies are contradictory.

A Spanish study involving over 4,000 cycles showed that at levels above 1.5 ng/mL on the day of trigger, the rate of ongoing pregnancy following a fresh transfer fell to 19 per cent, compared with 31 per cent at lower levels. A meta-analysis of 63 studies confirmed this effect following a fresh transfer, but not in the case of frozen embryo transfers or egg donation: the endometrium and the timing of the procedure are the main factors involved. The 2025 version of the ESHRE guideline considers that it is probably beneficial to measure progesterone levels on the day of trigger injection when a fresh transfer is planned.

In practice, if the level is high, the clinic often suggests freezing all the embryos and transferring them during a subsequent cycle. The embryos suffer no harm from this delay.

Progesterone prior to a frozen embryo transfer

This is the situation in which progesterone testing has become most important in recent years, particularly in hormone replacement (HRT) cycles, when the endometrium is prepared using hormones and all the progesterone comes from the treatment.

• A prospective study published in 2021, involving 1,150 patients treated with vaginal progesterone, showed that below 8.8 ng/mL on the day of transfer, the rate of ongoing pregnancy was 37 per cent, compared with 54 per cent above that level. Around three in ten patients were below this threshold.
• A meta-analysis published in the same year identified a threshold of around 10 ng/mL: above this level, the chances of a viable pregnancy or live birth were approximately 1.5 times higher, and the risk of miscarriage was lower.
• When levels are low, some clinics administer progesterone via subcutaneous injection and proceed with the transfer. In a study published in 2021, patients whose levels were ‘brought up’ in this way achieved results comparable to those with normal levels. This result is encouraging, but it comes from a non-randomised, single-clinic study.

Two points are worth noting. Firstly, these thresholds mainly apply to vaginal progesterone in a hormone-replacement cycle; with injections, or in a natural cycle where the corpus luteum produces its own progesterone, the reference values are different. Secondly, the blood level varies depending on the time of the last dose: make a note of this on the day of the blood test. The treatment itself is detailed in the article on progesterone after transfer.

How to interpret your result

• What is the unit: ng/mL or nmol/L, pg/mL or pmol/L?
• On which day of the cycle, and how many hours after the last dose of progesterone?
• What type of cycle: stimulation for fresh transfer, hormone replacement (HRT) cycle, natural cycle?
• What threshold does your clinic use, and what does it recommend if your result is below it?

If you receive a result that you do not understand, or if you have the blood test done at home and need to pass the figure on to the Greek clinic, please write to me: I’ll liaise with them and check the units first.

Frequently asked questions

Source: https://fertilitegrece.com/en/blog/estradiol-progesterone-levels-ivf/ — Triada Baloukoudis, IVF patient coordination in Greece. General information, not medical or legal advice. Printed on

Triada Baloukoudis
Independent IVF patient coordinator in Thessaloniki, with 24 years of experience supporting patients travelling from abroad. More · Contact · Facebook