Scientific Introduction to Female Reproductive System and Birth Control

Written by: Lisa Cheng

Disclaimer

Please note that, while the information within these articles is fact-checked, it is NOT medical advice. We strongly suggest that you seek complete information from your healthcare professional for your specific health needs. [Termination of pregnancy is not a topic that will be discussed within this article.]

Birth Control Options and the Menstrual Cycle

Conversations surrounding birth control remains a taboo subject in some cultures, yet it is extremely important to educate women about this topic to allow them to make informed choices about their health. Birth control or contraception are actions taken to prevent unintended pregnancy – common examples include condoms, oral contraceptives (i.e., hormonal birth control pills and emergency birth control pills), vaginal rings, and intrauterine device (IUD). The reason for their uses extends further than family planning to include women’s health, such as mental health, hormonal regulation, and protection against sexually transmitted infections.

An understanding of the menstrual cycle and how the female body prepares for a possible pregnancy, and thus the possible targets in the process to prevent pregnancy, must first be established. The menstrual cycle experienced by pre-menopause women typically range between 24 to 38 days and characterized as three phases: before egg release, release of the egg, and after egg release. Hormones are important factors that influence the events of the menstrual cycle. The beginning of the cycle is marked by low estrogen and progesterone levels in addition to the first day of bleeding, an indication of the thining of the uterine wall. At the same time, there is a slight increase in follicle-stimulating hormone which stimulates the production of follicles (fluid-filled sacs) in the ovaries.

Each follicle contains one egg and multiple follicles will simultaneously grow, but only one will reach maturity and when it does, it will release estrogen which causes the other follicles to break down. At the peak of estrogen levels, luteinizing hormone surges and then the egg is released from the follicle (ovulation). The ruptured follicle will form a structure called the corpus luteum which stimulates increase in progesterone levels.

Progesterone functions to prepare the uterus in case of egg fertilization and subsequent embryo implantation by inducing a thickened endometrium (i.e., uterine lining) with fluids and nutrients, more viscous mucus to prevent sperm entry, and a slight increase in body temperature. Generally, there are six to nine days in each menstrual cycle where pregnancy can occur, but the window which this can happen varies among women, and two outcomes are possible:

1.     When the egg is fertilized (i.e., a sperm has penetrated the egg), it will attach itself to the uterine wall. [In some cases, the egg will not implant into the uterus but rather grows outside the uterine lining resulting in an ectopic pregnancy.]

2.     After approximately 14 days where no implantation occurs, the thickened lining of the uterus expelled as blood through the vagina (i.e., period).

In this article series we will focus on the second outcome where there is no implantation indicating that there are no signs of pregnancy. Birth control options are designed to inhibit the occurrence of certain events leading to embryo implantation.