Whether or not you and your partner are trying to get pregnant, it will be helpful to first understand how the female body works in relation to fertility or if we use the medical term, then for ‘reproduction’. This simple beginner’s guide will take you through the complex basics of female anatomy as well as key hormones relevant for female fertility.
ABC of ‘How a woman gets pregnant’
In very simple terms, the man’s sperm and the woman’s egg unite and form a tiny ‘embryo’ through a process called fertilisation. This tiny embryo attaches itself in the womb of the woman usually and leads to her becoming pregnant. About nine months down the line, the woman either goes in labour or has a caesarean section and a baby arrives.
Now let’s break it down further to know exactly how all these steps work. We will talk about the female internal organs that are key to female fertility, the menstrual cycle, hormones and what it takes to achieve a pregnancy naturally.
Female reproductive organs
- The womb (uterus) and its neck (cervix)
- The fallopian tubes
- The ovaries
- The vagina
The womb (uterus) and the tubes (fallopian tubes)
The womb (uterus) is a pear shaped structure which has two parts – the upper part is the body of the womb and the lower part is the neck of the womb (cervix). The neck of the womb opens inside the vagina. The upper part of the cavity of the womb is attached to a fine tube (fallopian tube) on each side. The fallopian tubes connect at the other end to the ovaries.
Ovaries are two small oval ‘almond sized’ structures located on either side of the womb and connected to the far end of the tubes.
Where do eggs come from?
The eggs come from the two ‘ovaries’ which are located deep inside the belly (pelvis) of a woman. The ovaries contain eggs as well as other surrounding cells that make different type of hormones.
Menstrual cycle of a woman
The first day of a period when a woman bleeds is referred to as day one of the cycle. Most women will have regular monthly cycles of approximately 28 days. However, it is fairly normal to have a cycle that varies between four to six weeks.
An ovulation, or release of an egg, occurs about halfway through a regular cycle (around 12-16 days). Sometimes, more than one egg can be released in the same cycle.
Hormones are chemical signals that are released into the blood stream and act on different organs. Bodies produce lots of different types of hormones e.g. insulin which is a hormone that is crucial in keeping both men and women’s blood sugars in check. Hormones such as estrogen (also spelled oestrogen) are considered important for female fertility as well as to maintain general and sexual wellbeing, heart health, bone health and brain functioning.
Hormones are released from the ovaries in response to signals from the brain. The eggs within the ovaries drive this process. As a woman gets older and reaches menopause, her ovaries shrink in size, she stops releasing eggs as her stock of eggs become sparse and she stops producing hormones such as estrogen.
How and why does periods happen?
A female goes through cyclical (monthly) changes in their hormones which serves two main purposes in relation to female fertility:
- It makes the ovaries release an egg, and
- It makes the womb lining ready to accept a pregnancy if it happens.
If a pregnancy does not happen in any given month, then the hormone levels start to fall. This results in the lining of the womb being shed into the vagina, along with bleeding. This is called a period, or ‘menses’’. This makes the womb lining thin so it can regrow again for the next cycle, ready for the next egg to create a pregnancy.
How do ovaries make and release eggs?
Women are born with a fixed number of eggs at birth. The actual number of eggs varies from female to female. These eggs are kept quiet in a dormant ‘sleeping’ stage for many years. As girls grow older and go through puberty, the ovaries and the mechanics of the reproductive system kick-starts the cells within the ovaries to produce hormones. Two key hormones are estrogen and progesterone. The changes in the hormone patterns make the eggs within the ovaries to grow and mature. This eventually results in the release of an egg, a process called ‘ovulation’. It is important to know that not all eggs grow together as the cohort of eggs are meant to last the life span of a woman’s fertile years until she goes through the ‘change’ or ‘menopause’.
The eggs and hormones made within the ovaries are directed by messenger hormones (follicle stimulating hormone and luteinising hormone) released in the blood stream by a tiny gland in the brain, called the ‘pituitary gland’. This gland receives a message from a small structure above it called the hypothalamus. The hypothalamus, the pituitary gland and the ovaries work together by sending signals in an orderly fashion to coordinate every monthly cycle. In any given cycle, there are a certain number of potential eggs that receive a hormonal message to begin maturing – this can be anywhere from a few to over 40. However, the very specific hormonal messages from the hypothalamus, pituitary gland and ovaries are so highly regulated that eventually only one (sometimes two) of these eggs is released in that month. The other eggs will eventually perish.
The sequence of events for egg production is summarised below:
The hypothalamus sends a signal to the pituitary gland which in turn sends a signal to the ovary. The ovary decides to make the hormones which in turn act on the eggs to make them grow bigger in a fluid filled bubble called a follicle. Once the follicle containing the egg becomes a big enough size, it sends signals to the pituitary gland to then send a boost dose of a hormone trigger called Luteinising Hormone (LH), which makes the follicle release the egg. Once the egg is released from the ovary, the cells within that follicle in the ovary make a hormone called progesterone.
The pituitary also then stops sending further hormonal signals to the rest of the smaller follicles that have also been growing under hormonal stimulation. This switches off the smaller ones from making a mature egg and leads to those eggs perishing. Some women wonder that because these smaller eggs perish, if they would run out of eggs at some point. In reality, women are born with more eggs than could ever be matured during her reproductive years, so the supply will not run out before menopause. It is important to know, however, that as women get older (in the years leading up to menopause), so do the quality of the eggs, as well as the ability of those hormones to get quality eggs to mature.
The eggs are really tiny, and it is very difficult to see them through naked eye. One can say, a fertilised egg (embryo) is as tiny as a speck of dust.
How does an egg and sperm reach the womb?
The egg, once released from the ovary, passes through a fine tube called the fallopian tube, which is connected to the womb. The sperm swims up from the vagina and reaches the tube too, making a journey from the vagina through the womb and then to the tube. The sperm meets the egg in the tube and penetrates the eggshell to ‘fertilise’ the egg. If fertilisation happens, the egg is now referred to as an ‘embryo’. The embryo then moves down in the tube towards the womb cavity. Once it reaches the cavity of the womb, it hatches out of the eggshell (which protects the egg until this point) and attaches itself to the womb lining, if all is well. Roughly, it will take about 5 days from the release of the egg to embryo attaching itself in the womb.
If the egg does not fertilise or an embryo does not attach to the womb lining, then it will either perish on its own or come out along with the shedding of the womb lining during the menses/period.
Does timing and frequency of sex matters to achieve a natural pregnancy?
To achieve a natural pregnancy, the sperm needs to fertilise an egg soon after its release (ovulation time). It is believed that a sperm can survive in the fallopian tubes for about a week maximum (usually 3-5 days). However, the egg survives for roughly 24 hours after its release from the ovaries. Hence, if one is having regular sex every two-three days or 2-3 times in a week, then the sperm would be able to fertilise an egg whenever it is released, as there will always be sperm around.
How long does it take to achieve a natural pregnancy?
It is normal to take up to one year to achieve a pregnancy through regular unprotected intercourse. Some women may take up to two years to achieve this. However, if any of the above mentioned female reproductive organs are not functioning properly or there are problems with sperm, it can cause delay in achieving a pregnancy.
Please read our other sections that cover this in more detail including lifestyle, tests and treatment options to achieve a pregnancy.