Luteal phase support: the progesterone after transfer

In a natural cycle, after ovulation the corpus luteum in the ovary produces progesterone, the hormone that transforms the lining of the womb from its growth phase into the phase that awaits the embryo. Without enough progesterone, the lining does not remain suitable and pregnancy cannot continue. This period is called the luteal phase.

In a stimulated IVF cycle, the medications used to prevent premature ovulation and the egg retrieval itself disrupt this natural production. The corpus luteum does not work properly, and the progesterone level falls. Progesterone is therefore given from outside, from the day of egg retrieval or transfer, to keep the lining ready. In frozen embryo transfers with hormonal preparation, where there is no ovulation at all, external progesterone is the only source and is absolutely necessary.

Progesterone is given in several forms: vaginal (gel, pessaries, tablets), by intramuscular or subcutaneous injection, and in some cases orally. Large studies have shown that vaginal and injectable forms give comparable pregnancy results when used correctly; many centres therefore use the vaginal form widely, because it avoids daily injections and is well tolerated.

This does not mean all forms are the same for everyone. Some patients have local side effects from the vaginal form; in others, especially in certain types of frozen cycles, the team may prefer the injection or a combination, sometimes after measuring the blood progesterone level. The choice is clinical and individual, not a matter of the 'best form' in general.

If you miss a dose, take it as soon as you remember, without doubling the next one, and tell the team if the delay was long; a late dose rarely changes the outcome. Light bleeding or spotting while using the vaginal form is common and does not in itself mean something has gone wrong; it should be reported, but not cause panic.

Side effects such as tiredness, bloating, breast tenderness and mood changes are common and are often mistaken for signs of pregnancy or of its absence. In fact they come from the progesterone itself and say nothing about the outcome. This is one of the reasons the two-week wait is so hard and why the test is done only on the set date.

Progesterone continues until the pregnancy test and, if it is positive, usually until around week 10–12, when the placenta takes over progesterone production. In frozen transfers with hormonal preparation this duration is particularly important, because there is no corpus luteum to help. The exact duration is set by your team according to the type of cycle.

What should not be done is to stop progesterone on your own, because 'I feel fine' or because a test came out negative before the date. Stopping early in an early pregnancy can be harmful. If the test is negative on the set date, the team will tell you when to stop; if it is positive, they will tell you how long to continue.