The Menstrual Cycle, Ovulation and the Fertile Window
Most of us were taught the menstrual cycle once, quickly, and at an age when getting pregnant was the opposite of the goal. Then it becomes the goal, and the details turn out to matter.
This is the sequence, one step at a time, with the source for each step.
When does the cycle actually start?
On the first day of bleeding, not at ovulation and not at the end of your period. That convention is what every other date in the cycle is counted from, so it is worth being sure of.
The menstrual cycle starts the day the period starts, and ovulation occurs once each cycle.
Multiple health authorities agree
Clinical review pending
More than one independent health authority states this.
The first day of bleeding is considered the first day of the menstrual cycle... Around day 12 to 14 in an average 28-day cycle, the egg is released from a follicle on the ovary in a process called ovulation.
Approximately every 28 days a pulse of hormones triggers several eggs to ripen.
Stated in a health authority's guidance
Clinical review pending
A health authority states this in its published guidance.
"During the follicular phase, the hypothalamus... releases gonadotropin-releasing hormone (GnRH). This hormone tells the pituitary gland to release follicle-stimulating hormone (FSH), which travels through the blood to the ovary. Each month, the brain causes the release of FSH to stimulate the development of a number o…
A hormone surge, then a follicle releases an egg, then the egg travels. The whole event is quick, and the window it opens is short.
A hormone burst causes the follicle to pop and release the egg into the fallopian tube, where fertilization by sperm can occur.
Multiple health authorities agree
Clinical review pending
More than one independent health authority states this.
"The LH surge increases intrafollicular proteolytic enzymes, weakening the wall of the ovary and allowing for the mature follicle to pass through." ... "Once the follicle is released, it is caught by the fimbriae of the fallopian tubes." ... "taken up by the fimbriae of the fallopian tube where it has the potential to…
At ovulation a mature egg is released from an ovary into a fallopian tube; sperm entering an egg there results in pregnancy.
Stated in a health authority's guidance
Clinical review pending
A health authority states this in its published guidance.
"Ovulation is a physiologic process defined by the rupture of the dominant follicle of the ovary. This releases an egg into the abdominal cavity. It then is taken up by the fimbriae of the fallopian tube where it has the potential to become fertilized."
Five, working in sequence rather than in isolation. Knowing their names makes lab results and doctor's appointments considerably less opaque.
Hormones are chemical messengers, and five hormones are essential for fertility: GnRH, FSH, LH, estrogen, and progesterone.
Stated in a health authority's guidance
Clinical review pending
A health authority states this in its published guidance.
GnRH page: "It controls the production of luteinising hormone and follicle stimulating hormone from the pituitary gland... Follicle stimulating hormone and luteinising hormone control the levels of hormones produced by the testes and ovaries (such as testosterone, oestradiol and progesterone)... A deficiency of gonadot…
Around ovulation, and that is the whole answer. Timing is the single lever with the most consensus behind it of anything on this site, which is unusual for fertility advice.
Having sex during the days around ovulation is the best way to increase chances of getting pregnant, though ovulation timing varies even with tracking apps.
Multiple health authorities agree
Clinical review pending
More than one independent health authority states this.
The highest pregnancy rates are seen when partners have intercourse every 1 to 2 days during the fertile window... The fertile window... is usually the 6 days just before the day of ovulation.
Later than most people assume, and not at fertilization. There is also a quirk in how pregnancy weeks are counted that makes you roughly two weeks pregnant before conception happened, which is confusing the first time you meet it and standard everywhere.
Pregnancy officially begins once the blastocyst attaches to the endometrium.
Multiple health authorities agree
Clinical review pending
More than one independent health authority states this.
Pregnancy results if the egg becomes fertilized and implants in the lining of the uterus (endometrium).
Doctors typically count pregnancy weeks from the last period, and ovulation takes place about two weeks after the last day of the period.
Stated in a health authority's guidance
Clinical review pending
A health authority states this in its published guidance.
"A normal pregnancy lasts about 40 weeks from the first day of your last menstrual period (LMP)... Pregnancy is assumed to start 2 weeks after the first day of the LMP."