Your Menstrual Cycle and Conception
Most of us spend the first part of our reproductive years trying not to get pregnant. When you’re finally ready, it can be hard to know where to start. Knowing how a woman’s reproductive system works is helpful, as timing really is everything when it comes to conception.
The Menstrual Cycle
Your menstrual cycle consists of two distinct phases, the follicular phase and the luteal phase, which are separated by an event called ovulation. A menstrual cycle is defined from the first day of menstrual bleeding (called day 1) of one menstrual period to the first day of menstrual bleeding of the next. An average menstrual cycle lasts 28 days, but can range from 21-35 days. The luteal phase should be around 14 days long, regardless of the length of the menstrual cycle, whereas the follicular phase can be longer or shorter in different women.
The follicular phase starts on the first day of your menses and ends at the time of ovulation, which occurs around day 14 in a 28-day cycle. During the follicular phase, your pituitary gland produces two hormones: follicle stimulating hormone (FSH) and luteinizing hormone (LH). FSH works to recruit follicles (or the sacs that hold the eggs) in the ovaries, and will ultimately result in the recruitment of a dominant follicle that will be released during ovulation. The dominant follicle produces estrogen, which helps to build the lining of the endometrium, changes the quality of the cervical mucus to be thin and slippery, and triggers the production of the luteinizing hormone.
Following a surge of luteinizing hormone (LH), the dominant follicle will rupture, and ovulation will occur.
The luteal phase lasts from ovulation until menstruation. The follicle that burst to release the egg becomes a gland called the corpus luteum, and begins to secrete progesterone to stabilize the uterine lining and prepare it for implantation. Following ovulation, the egg is viable for 12-24 hours, after which it will degenerate if it is not fertilized. Sperm, however, can live inside the female reproductive tract for up to 5 days. You have the highest probability for conceiving by having unprotected intercourse starting 1-2 days prior to ovulation (which should coincide with a positive result from an ovulation predictor kit) and continuing daily until ovulation occurs as indicated a 0.5 degree rise in your basal body temperature or an elevated progesterone level in your blood.
Once the egg is ovulated, it is picked up by the fallopian tube and transported towards the uterus. If intercourse is timed correctly, sperm should be waiting in the fallopian tubes and be ready to fertilize the egg. When the sperm penetrates the egg, fertilization occurs. The fertilized egg, or zygote continues to travel down to the uterus for implantation.
Implantation occurs when the zygote attaches itself to the uterine wall. Implantation happens 7-10 days after ovulation. Once attached to the uterine wall, the embryo and developing placenta will begin to produce human chorionic gonadotropin (hCG), a hormone that stimulates the corpus luteum to continue making progesterone. Three to four weeks after your last period, your hCG levels should rise high enough to test positively in a home pregnancy test.
During implantation, some women may experience a small amount of bleeding or spotting, which is known as implantation bleeding. Also called implantation spotting, this normally occurs a week to a few days before a woman’s period would start. Around one-third of women experience some kind of implantation bleeding, which looks like a discharge with pinkish or brownish blood. This type of bleeding is not harmful and does not require medical attention.
Dr. Sydney Chang is a Fellow in Reproductive Endocrinology and Infertility at the Icahn School of Medicine at Mount Sinai/Reproductive Medicine Associates of New York. She earned her Bachelor of Arts in Human Biology at Stanford University, where she graduated with Honors and Distinction. She went on to complete her medical school education at Duke University School of Medicine. She completed her residency in Obstetrics, Gynecology, and Women’s Health at the Albert Einstein College of Medicine, where she served as an administrative chief resident.