The truth about Norethisterone and IVF
Norethisterone is sometimes prescribed prior to an IVF treatment cycle, whether that’s using your own eggs, donor eggs or an FET. An alternative to birth control pills, Norethisterone controls your cycle before your stimulating medication. Here’s how and why the drug is used.
Norethisterone is a synthetic form of progesterone, the vital pregnancy hormone that optimises your uterine environment and sustains your pregnancy. In your natural menstrual cycle, the body is producing progesterone in spades midway through your cycle. But fertility patients sometimes have irregular bleeds, making a medicated fertility cycle hard to plan. Patients with regular cycles may still want to time their fertility treatment, particularly if they’re travelling abroad for their treatment and need to book flights and time off work. Norethisterone makes this possible.
Birth control pills (BCPs) normally regulate a cycle before the stimulation phase to address these concerns. But BCPs don’t agree with everyone. Those over 40, with high blood pressure or with a history of aura migraines are the first to get a ‘no’ from their GPs. Why? Because BCPs are less natural than Norethisterone. Containing an equal dose of estrogen and progesterone, combined BCPs trick the body and don’t mimic the natural cycle. No wonder some women react badly to them. Norethisterone is just one hormone (progesterone) and fools the body in a much gentler way.
By taking Norethisterone from roughly mid cycle (typically 10mg daily) fertility patients can extend their menstrual cycle, delaying their bleed. Typically you can extend it by up to 10 days – sometimes less, sometimes more. Or you can use it to bring it on in the first place, if your bleeds are unpredictable. This bleed control gives fertility clinics the means to get you to bleed when it wants you to. Progesterone levels drop towards the end of a natural cycle. It’s this hormone drop that precipitates the bleed. Taking Norethisterone keeps your progesterone levels high. When you stop taking the pills, the hormone crash brings on your bleed three to four days later.
Timing the bleed that marks the start of your medicated cycle offers less flexibility than BCPs. The latter can regulate your cycle if started on day 1 to 4 of your bleed. But you can’t take Norethisterone for too long. So your bleed window is shorter. Very roughly, you need to start Norethisterone about six weeks before your estimated egg retrieval or transfer. You may need to adjust your treatment date if your bleed pattern is not quite aligned to this.
In summary, Norethisterone is medically safer than BCPs for controlling your bleed prior to your fertility treatment cycle. But it’s more complicated to time than BCPs. Talk to your clinic to see which route will work best for you.