The luteal phase is the phase of the menstrual cycle that occurs after ovulation (the phase in which one of the ovaries releases a mature egg) and before the start of menstruation (the shedding of blood and tissue from the uterus each month). The luteal phase typically lasts for about 12-14 days, but the exact duration can vary from person to person.

During the luteal phase, a temporary structure called a “corpus luteum” forms in the ovaries. This structure is formed when the dominant follicle that released the egg during ovulation transforms into the corpus luteum. The corpus luteum is an endocrine gland that is responsible for producing hormones, especially progesterone and some estrogen. These hormones are essential for preparing the lining of the uterus (also called the endometrium) for the possible implantation of a fertilized egg.

Specifically, as the body’s progesterone levels rise during the luteal phase, the lining of the uterus thickens. This makes the endometrium more suitable for a fertilized egg to attach and develop. The increase in hormone levels also causes the cervical mucus to thicken as a protective measure that helps prevent bacteria from getting inside the uterus.

If fertilization occurs and the egg is successfully implanted in the uterine lining, the corpus luteum continues to produce progesterone to support the early stages of pregnancy until the placenta takes over hormone production.

However, if fertilization does not occur, the corpus luteum eventually breaks down and degenerates, leading to a decrease in progesterone and estrogen levels. This hormonal drop triggers menstruation, which marks the start of a new menstrual cycle.

While 12-14 days is the average length of the luteal phase, people may experience shorter or longer luteal phases. A luteal phase of 10 days or less may not allow the uterine lining to thicken enough to support a fertilized egg. As a result, people with shortened luteal phases may struggle to get pregnant.

On the other hand, people with long luteal phases of 18 days or more may have a hormonal imbalance like polycystic ovary syndrome (PCOS). If you are struggling to get pregnant or experience symptoms such as missed periods, excessive hair growth, or unexplained weight gain, make an appointment with your health care provider to talk about it.

The luteal phase is a critical part of the menstrual cycle because it prepares the body for a potential pregnancy. If fertilization does not occur, the hormonal changes that occur during the luteal phase lead to the shedding of the uterine lining, resulting in menstruation, and the cycle begins again.

References:

• Cleveland Clinic. (2022, November 4). Luteal Phase. https://my.clevelandclinic.org/health/articles/24417-luteal-phase
  
  
• Kol, S. (2021). Time, time, time: see what governs the luteal phase endocrinology. Gynecological Endocrinology, 37(9), 775-777.