The luteal phase corresponds to the second half of the cycle in women. What happens during this period? What is the role of hormones at this time? Why is the luteal phase so important if a pregnancy is scheduled?
The different phases of the cycle
The female cycle that begins on the first day of menstruation physiologically comprises two phases: the follicular phase and then the luteal phase, of similar duration and separated by ovulation
During the first phase, called the follicular phase, a follicle (contained in one of the ovaries) will grow, ripen, and eventually rupture, letting an egg escape. It is ovulation that occurs in the middle of the cycle. During this first phase of the cycle, while developing, the follicle makes hormones: estrogen.
After ovulation, the second phase of the cycle is set up: the luteal phase ...
What happens during the luteal phase?
The luteal phase has 2 phases:
- The glandular transformation phase from the 15th to the 21st day: under the combined action of estrogen and progesterone, which has just appeared after ovulation, the glands present in the thickness of the uterine lining become more important.
- The glandular secretion phase from the 22nd to the 28th day: the glands and small arteries developed in the mucous membranes.
This is exactly how it works:
After ovulation, a follicle breaks, changes and forms a kind of small gland called yellow body.
In addition to estrogen, the corpus luteum then secretes progesterone, the hormone of motherhood, whose essential function is to prepare the endometrium for implantation of the embryo.
In case of fertilization (encounter of a spermatozoon with an egg), the corpus luteum continues its secretions of hormones allowing the pregnancy to be well put in place.
Without fertilization, the life of the corpus luteum is limited to twelve days, after which it involutes and disappears. Hormonal levels fall, the rules occur. Depending on ovulation, the duration of the luteal phase may be shorter.
What effects do ovarian hormones have on the endometrium?
During the first part of the cyle (follicular phase) under the influence of estrogen, the uterine lining gradually thickens. And the glands of the cervix produce cervical mucus, a clear, viscous liquid that is essential for the sperm to rise to the egg.
In the second part of the cycle, that is to say during the luteal phase, under the influence of progesterone, the lining of the uterus is transformed and ready to receive the egg (in case of fertilization between a spermatozoon and the egg). The cervical mucus thickens and becomes impermeable to spermatozoa (which will no longer move towards the uterus).
In the absence of fertilization, the progressive desquamation of the lining of the uterus over a few days will constitute the rules (or menstruation).
To understand better, here is a schematic presentation of ovulation and rules:
Author: Dr. Nicolas Evrard
Expert consultant: Dr. Alain Tamborini, gynecologist.