The menstrual cycle and how it affects fertility treatments

Ovarian stimulation and, in general, the different phases of assisted reproduction treatments are closely related to the menstrual cycle. This is precisely why we strive towards synchronising the processes involved in assisted reproduction with the menstrual cycle. Each phase of the cycle has a direct influence on fertility and on the success of techniques such as artificial insemination or in vitro fertilisation (IVF). Therefore, if you are trying to conceive and have considered using an assisted reproduction treatment, understanding your menstrual cycle can help you understand and face the process with greater confidence.

What is the menstrual cycle and how is it related to fertility treatments?

The menstrual cycle is a natural process that prepares your body for a possible pregnancy. It lasts approximately 28 days, although it can vary between 23 and 35 days. Regardless of the number of days it lasts, the stages of the menstrual cycle are the same, each with an essential role in reproduction:

1-Menstruation: This is the beginning of the menstrual cycle and coincides with the shedding of the endometrium, which is released in the form of bleeding when there has not been any embryo implantation.

2-Follicular phase: This pre-ovulatory phase, which begins with menstruation, is the stage in which follicles develop inside the ovaries. Not all follicles that begin to develop reach maturity. Normally, only one of these follicles will reach full maturity and release a mature egg ready for fertilisation.

In fertility treatments, this phase is key, as it is when medication is administered for ovarian stimulation, in order to promote the growth of multiple follicles and the maturation of several eggs to increase the chances of pregnancy.

3-Ovulation: In this phase of the menstrual cycle, the follicle ruptures and releases the mature egg into the fallopian tube, where it will remain waiting for a sperm to fertilise it. This generally occurs around day 14 of the cycle. This is the most fertile time in a woman’s cycle, as there is a greater chance of pregnancy if you have unprotected sex. Unless fertilisation occurs within 24 hours of ovulation, the egg will age and will no longer be able to be fertilised.

During ovulation, the eggs are at their most mature and can be fertilised, which is why this is the optimal time for procedures such as artificial insemination or ovarian puncture in IVF. To do this, ultrasound scans are used to monitor and determine, through medication, the exact moment of ovulation. This way, we can schedule the insemination or egg retrieval in an IVF with the best conditions and the greatest chance of success.

4-Luteal phase: This phase begins just after ovulation and lasts for a limited period (between 12 and 14 days) until the end of the cycle, when menstrual bleeding returns. In this post-ovulation stage, the ovarian follicle becomes a corpus luteum and begins to secrete progesterone to support the pregnancy and prepare the uterus, which becomes receptive to receive the embryo and facilitate its implantation.

In assisted reproduction treatments, hormonal support in this phase is fundamental to favour implantation and increase the chances of pregnancy, both in the case of artificial insemination and in the case of IVF following embryo transfer.

Furthermore, in cases where we do not transfer the embryo, there is the option of doing a second round of ovarian stimulation to take advantage of another wave of follicular growth that takes place at this stage of the cycle, with the aim of accumulating and having a greater number of oocytes and maximising the possibilities in the same cycle.

5-Ischemic phase: If the released egg is not fertilised by a spermatozoid, the corpus luteum disappears. Consequently, the production of oestrogens and progesterone gradually decreases in what is known as the ischemic phase of the menstrual cycle. This decrease in sex hormones causes the endometrium to shed and be eliminated through the vagina, resulting in menstruation and beginning a new cycle.

How do you control the cycle in assisted reproduction?

Assisted reproduction specialists carefully study every patient’s menstrual cycle in order to personalise treatments. Some key aspects for controlling the cycle are:

Controlled ovarian stimulation

This is the first step in assisted reproduction treatment, whether it be artificial insemination (AI) or in vitro fertilisation (IVF). This is also a necessary step when a woman wants to vitrify her eggs to preserve fertility, or in the case of egg donors.

Ovarian stimulation aims to achieve the maturation of several follicles at the same time in the ovaries, in order to increase the number of oocytes to be fertilised and, thus, the number of embryos and the possibility of achieving a pregnancy.

Using different hormones, we try to synchronise the follicles so that they all grow at the same time until they reach an adequate size and fully mature.

Ovulation scheduling and follicular puncture

Using ultrasound scans and hormone analyses we can monitor your cycle and determine the exact moment of ovulation so that we can schedule insemination or egg retrieval in an IVF cycle.

It is very important to schedule the follicular puncture for oocyte retrieval 36 hours after the injection of hCG, the hormone that completes the maturation of the oocytes. If more time passes, ovulation occurs, causing the mature eggs to be expelled from the ovaries into the fallopian tubes.

Embryo transfer in natural or surrogate cycle

Embryo transfer is a simple and painless process, but it is essential to do it when the endometrium is ready, that is, when it is receptive. The transfer can be done when the embryo is in the zygote stage, which is day 2 of embryonic development, or in the morula stage. However, the most common practice today is to transfer the embryo on day 3 or day 5 (in the blastocyst stage).

The transfer can be done in the same cycle in which the embryos were created, without freezing them. This is known as a fresh transfer. But we can also make the transfer in a subsequent cycle, in which case the embryos have to be frozen. Delayed or frozen transfer is used in an attempt to increase endometrial receptivity by avoiding the impact of the hormones used in the stimulation phase on the endometrium, potentially improving the pregnancy rate.

In these cases, specialists may choose to use a natural menstrual cycle without hormonal medication, while in other cases a surrogate and better controlled cycle is preferred to prepare the endometrium. In both cases it is essential to monitor the menstrual cycle of the patient to know the best time to perform the embryo transfer and achieve pregnancy.

Supplements in the luteal phase

To achieve better endometrial development, exogenous progesterone is commonly administered orally or vaginally in all assisted reproduction protocols. These hormonal supplements favour embryo implantation and improve endometrial receptivity.

As you can see, understanding your cycle is the first step towards making informed decisions and understanding how assisted reproduction treatments adapt and develop according to the menstrual cycle.

At Tambre, we are experts in assisted reproduction. We use the most advanced techniques to diagnose and treat a range of fertility problems, including irregular menstrual cycles and hormonal imbalances. Our team of specialists analyses the evolution of each phase of the cycle to personalise the procedures and optimise the chances of pregnancy. For more information on how we can help you on your journey to motherhood, contact us or call us on +44 (0) 20 38 688 650 to request your first consultation.