The female reproductive system
The female reproductive system is almost entirely internal.
The vagina is the canal that leads from the outside of the body to the cervix, the opening to the uterus. The cervix contains cells that produce mucus, which around the time of ovulation creates channels for sperm to swim through.
The uterus is the muscular organ in which a fertilised egg can develop into a baby. It is the size and shape of a small pear and lined with a blood-rich and nourishing lining, the endometrium.
The endometrium thickens after ovulation to provide a potential bed for an embryo to implant and grow a placenta. The drop in hormones approximately 14 days after ovulation results in the shedding of this lining. The myometrium is the muscular layer that contracts during a period.
The fallopian tubes extend from the ovaries to the top of the uterus. The ovaries contain the eggs and are about the size of walnuts.
The eggs in each ovary are made before a woman is born. They reside in the ovaries as immature eggs until they die off or are selected to mature.
Every month from puberty to menopause, eggs begin to mature inside several fluid filled 'cysts' called follicles. Each group of eggs begins development 3 months prior to an ovulation so that waves of maturing eggs occur throughout a woman's life.
Only one follicle from each group will become dominant, while the others will shrink away. The dominant follicle releases an egg at ovulation, which then travels down the fallopian tube toward the uterus.
Sperm swim up to fertilise an egg as it travels down the fallopian tube. The developing embryo then travels down the fallopian tube to the uterus, where it implants in the endometrium approximately one week after ovulation.
Figure 1. The female reproductive system
Hormones control the highly complex sequence of events leading to ovulation and those that prepare the endometrium for a potential pregnancy.
The main ones are – follicle stimulating hormone (FSH), luteinizing hormone (LH), oestrogen and progesterone. Other hormones that affect the reproductive system include testosterone and prolactin.
The pituitary gland in the brain produces FSH and LH that convey messages to the ovary.
The actions of these hormones result in three phases in the monthly menstrual cycle.
The menstrual cycle
According to Dr Karin Hammarberg, a fertility expert and senior research fellow at Melbourne’s Monash University, “the simplest way of improving your chance of conceiving when you want to, is to monitor your menstrual cycle.”
To do this, you’ll need to familiarise yourself with the menstrual cycle stages, of which there are three : the follicular phase, ovulation and the luteal phase .
1. The follicular phase
The follicular phase starts on the first day of your period, during which follicles in the ovary are stimulated by FSH to mature to produce one egg.
This phase is short and is the release of the egg into the fallopian tube. In response to rising oestrogen levels, the level of LH spikes up. This LH surge triggers the final maturation of the egg and the release of the egg.
This usually happens 14 days before the next period is due (eg. on day 14 of a 28-day cycle).
3. The luteal phase
The luteal phase begins after ovulation.
This is where the uterus lining thickens in preparation for a potential pregnancy. If the egg isn’t fertilised, the uterus lining sheds and your period begins.
Figure 2. The menstrual cycle
Conception is only possible over a period of about five days leading up to and including ovulation, Dr Hammarberg asserts.
“After ovulation, it’s not possible, because the egg only lives for 24 hours . Sperm can live for up to five days, so even if you have intercourse a few days before ovulating, the sperm can still fertilise the egg. But once ovulation has happened, it’s all over for that cycle and you just have to wait for the next one.”
How to calculate the menstrual cycle
In order to calculate a fertility window (generally a five-day window per cycle), it’s important to know when you’re ovulating.
This begins with charting how long your cycles are
Day one begins on the first day of your period; your cycle ends on the day before your next period. Those who have a period every 28 days, for example, tend to ovulate between day 12 and 16, but a woman with a 36-day cycle will ovulate between day 20 and 24 .
To save doing the maths yourself, you may wish to experiment with an ovulation calendar; there are several free tools, such as the Your Fertility calculator, available online.
It’s not advisable to rely on calculations alone, however – especially for those who have irregular periods.
According to Dr Hammarberg, observing cyclical changes in cervical mucus
can also be useful. “In the days leading up to ovulation, the mucus becomes quite liquid and stretchy, a bit like egg white,” she explains.
“I always think of it as the perfect medium for sperm to swim along.”
Charting these changes, along with keeping an eye on the calendar, can increase your chances of conception. In addition, an ovulation predictor kit can be helpful.
And if you feel it’s stressful to try to look for signs or count days on the calendar? “You may wish to just have intercourse every two to three days,” says Dr Hammarberg. “That should cover all the bases.”