General, Egg Freezing, IVF

Why Do You Start Fertility Treatment With Your Period?


6 min read

The only time a person suffering from infertility is excited to get their period is when it means they get to start treatment. Most fertility treatments are started on the second or third day of your period, known as cycle day 2 or 3.

Have you ever wondered “What is my body doing at the beginning of my period that makes it the perfect time to start treatment? What's the reasoning behind timing the start of treatment? What if I don’t get a period? What if I have an IUD?” Let’s look into these questions and more!

The Basics of The Menstrual Cycle

Here is a high level menstrual cycle diagram:

Menstrual cycle diagram

And a slightly different view of some of the hormones produced by your body:

Menstrual cycle diagram

Before we dig too deeply into why fertility treatments are started during your period, it’s important to know how the menstrual cycle works. The menstrual cycle is broken down into 2 main parts: the follicular phase and the luteal phase. 

  • Follicular Phase: The follicular phase begins on cycle day 1, which is the first day of full flow bleeding during your period, and ends with ovulation.

During the follicular phase, your body produces hormones called follicle stimulating hormone (FSH) and luteinizing hormone (LH), which stimulate your ovaries to grow a follicle. As the follicle grows, it produces estrogen. The estrogen slows the production of FSH and LH and causes the uterus to grow an endometrial lining, where a potential embryo could implant if a pregnancy occurred during this cycle.

  • Ovulation: Once the follicle is large enough to contain a mature egg, a surge of LH from the anterior pituitary causes ovulation.

The timing of ovulation can vary based on cycle length and cycle regularity. Ovulation triggers a change in hormones where the LH and FSH levels fall and the progesterone level rises to support a potential pregnancy.

  • Luteal Phase: The luteal phase begins after ovulation occurs and typically lasts around 14 days.

During this portion of the menstrual cycle, the remnants of the dominant follicle, known as the corpus luteum, produces progesterone. The progesterone changes the endometrial lining to make it optimal for embryo implantation. The progesterone would also support a pregnancy if that were to occur. If no pregnancy occurs, the progesterone levels begin to drop towards the end of the luteal phase and the withdrawal from progesterone causes your period to start. 

With the start of your period, your body starts the menstrual cycle over again. The important thing here is that in the first few days of your cycle, your body hasn’t yet started growing a follicle or endometrial lining, which makes this the perfect time to start fertility treatment.

What's the reasoning behind timing the start of treatment with your period? 

Fertility medications for ovarian stimulation are used to stimulate many of the tiny, immature antral follicles in your ovaries all to grow and mature at the same time, which gives you many eggs to work with when it comes time for egg retrieval. The best time to get started with treatment is on cycle day 2 or 3 of your menstrual cycle. On these days, your body has usually reabsorbed the corpus luteum from last month and is also shedding last month’s lining. 

The time when your ovaries aren’t working to grow a follicle and your lining has been shed is often called “baseline”. So the next question is, why do we want to start treatment when the body is at baseline? The reason is that once your body starts to grow its own dominant follicle, the other smaller, antral follicles won’t respond to fertility medications. The presence of a dominant follicle essentially turns the remaining follicles off. 

What would prevent me from starting treatment?

Sometimes, by cycle day 2 or 3 when you come in for your baseline ultrasound and bloodwork, your body hasn’t yet cleared the previous month’s corpus luteum. This is often referred to as a simple cyst. This type of cyst will resolve over time, so your doctor may tell you to come back in a week or two to check again to see if you can get started with your treatment cycle.

What if I don’t get a period or if my period is irregular?

As discussed, once your body has a follicle in the ovaries that is producing hormones, the remaining follicles don’t respond well to fertility medications, which is why for most people it is best to start on cycle day 2 or 3. There are, however, a few scenarios where you may be able to start randomly without a period.

  • Random start using birth control pills: Birth control suppresses the ovaries, which means that it prevents the ovaries from growing a follicle and allows the start of treatment to be much more flexible. This method is often used to manipulate cycles around the schedules of both patients and doctors.

  • Random starts for patients with irregular or infrequent cycles: Many times, patients who don’t get periods or get them very irregularly may have long periods of time where their bodies are not growing a follicle and their hormones remain at baseline levels. This can often be the case with patients with PCOS. Before randomly starting a cycle, you would go into the fertility clinic for a baseline ultrasound and bloodwork to confirm that all your hormones are low and there are no follicles growing in your ovaries. As long as your body appears to be at baseline, your doctor will be able to give you the go ahead to do a random start without waiting for a period.

  • If you have an IUD and do not get your period with it:  If you have an IUD and don’t get periods, you may be a candidate for a random start as well. This can depend on the type of IUD that you have, copper or hormonal, and whether or not you still ovulate with your IUD in. Your doctor may ask that you come into the clinic for a possible random start or to use ultrasound and bloodwork to assess what is going on in your body. This information will give guidance to your care team about when to start treatment.

If you don’t get regular periods, your doctor may prescribe something called Provera (medroxyprogesterone) to prepare you for a random treatment start. Provera is a progesterone pill that is typically taken for 7-10 days. Once the Provera is stopped, the withdrawal from the progesterone will cause you to have a period. That way, your body can shed the old endometrial lining and begin growing a fresh lining during the treatment cycle. This is especially important in cycles that involve a possible pregnancy, like timed intercourse, IUI, IVF with a fresh transfer and frozen embryo transfer cycles. 

Sometimes, waiting for your period to start can feel like an eternity when you are trying to get started with treatment, but there are many reasons why this timeframe is important. For most patients, starting fertility treatment on cycle day 2 or 3 of your period gives the best chances of success. Based on your medical and fertility history, your doctor will help you plan when and how to get your treatment process started.