Getting pregnant
Pregnancy is a complicated process that depends on many factors:
- The production of healthy sperm by the man and healthy eggs by the woman
- Unblocked fallopian tubes that allow the sperm to reach the egg
- The sperm's ability to fertilize the egg when they meet
- A genetically healthy embryo The ability of the embryo to implant in the uterus.
Repeatedly encountering difficulty at any of these steps can lead to infertility.
The reality is that human reproduction is a fairly inefficient process. In one cycle for the average fertile couple, the chance of fertilisation from any particular meeting of egg and sperm can be about 80%, but by the time of the expected menstrual period roughly half of the early embryos have already failed to develop.
Many of these lost embryos are fundamentally abnormal and are unable to survive. In fact, the menstrual period might not even be delayed and the couple not realise that an early pregnancy has been lost. If a menstrual period is missed, a quarter or more of the remaining embryos can still fail later.
Various clinical studies have calculated the chance of pregnancy among population groups who do not use contraception, and indicate that the probability of a live birth after exposure in any one month averages about 1 in 5, or a 20% chance.
The age factor
As you can see from the graph below, by age 36 a normal woman's chances of conceiving per month is decreased by half. The downward slope continues until by age 45 the average natural fertility rate per month is approximately 1%.
Reproduction in women
The female reproductive system is entirely internal.
The vagina is the canal that leads from the outside of the body to the cervix, the opening to the uterus.
The uterus is the muscular organ where a fertilised egg, or embryo, attaches and develops. It is the size and shape of a pear and lined with a rich and nourishing membrane, the endometrium.
The fallopian tubes extend from the top of the uterus down over the ovaries, the two walnut-sized organs that contain the eggs.
The eggs in each ovary are made before a woman is born. The most eggs a woman will ever have - about 7 million - is when there's still 20 weeks to go before birth. From this time on, the number of eggs will diminish in number, and none will be replaced. A girl is born with about 2 million eggs. At the time she has her first period there are about 400,000.
Every month from puberty to menopause, eggs begin to mature inside several fluid filled 'cysts' within the ovaries, called follicles. Only one of these follicles will become dominant, while the others will shrink and be absorbed by the ovary. At mid cycle, the dominant follicle releases a single egg during ovulation, which then travels down the fallopian tube toward the uterus.
For a pregnancy to occur, fertilisation happens in the fallopian tube, when the egg meets sperm. The developing embryo then travels down the fallopian tube to the uterus, where it will implant in the endometrium approximately 7 days after ovulation.
Hormones control the highly complicated sequence of events leading to ovulation. The pituitary gland in the brain produces the two hormones that the ovary needs:
- Follicle stimulating hormone (FSH)
- Luteinising hormone (LH)
As these hormones are released, the monthly menstrual cycle occurs in three phases:
Phases of the menstrual cycle:
- Follicular phase - this begins on Day 1 of the menstrual cycle, the first day of menstrual bleeding. FSH begins by stimulating the development of many follicles, but as levels of FSH gradually fall in a natural cycle only one follicle will dominate and go on to produces a mature egg. The non-dominant follicles are absorbed by the ovary and cannot be used again. The developing follicle also secretes estrogen, which has several functions. For example, estrogen develops the watery mid cycle changes in cervical mucus that assist the passage of sperm into the uterus and also causes the thickening of the endometrium required for implantation. The main estrogen the ovary produces is estradiol (E2).
- Ovulatory phase - this phase is short. It begins when, in response to rising estrogen levels, the level of LH rises dramatically. This LH surge triggers the final maturation of the egg, the rupture of the follicle, and then the release of the egg. This usually happens 14 days before the next period is due, or on day 14 of a 28-day cycle.
- Luteal phase - begins after ovulation. At this point, the ovarian follicle where the egg developed collapses and solidifies to become the corpus luteum. This very important structure mainly produces progesterone, the hormone necessary for transforming the endometrium so that a fertilised egg (the early embryo) can implant and develop. If conception does not occur, the corpus luteum stops functioning on about Day 26 of a 28 day cycle. Without the support of progesterone, the endometrium begins to break down and is shed in menstruation.
Reproduction in men
As with women, the hormones LH and FSH also control men's reproductive systems. Unlike women, however, the male reproductive system is both internal and external.
The testes lie in the scrotum, the pouch of skin located beneath the man's penis. The testes are the organs that produce sperm and testosterone.
From the testes, sperm pass slowly through the coiled channels of the epididymis, where they mature. Once sperm are mature, they move into the vas deferens, a tube that connects the epididymis with the urethra via a common ejaculatory duct.
The entire process of sperm formation takes approximately 72 days.
Natural fertilization
After sperm are deposited into the upper vagina via ejaculation, they must travel through the cervical mucus into the uterus and then into the fallopian tube before they can meet with the egg. Sperm are transported on this long journey by their own rapid forward movement assisted by upward contractions of the uterine walls. During the trip, sperm prepare themselves to meet the egg by subtle alterations of their heads and movement patterns.
When they meet the outer membrane of the egg, the sperm start to burrow through it and then enter the egg itself. At the moment the first sperm successfully penetrates the egg, a reaction is triggered that makes the egg resistant to all other sperm. This single sperm absorbs into the egg, where the genetic material contained in its head fuses with that of the egg. Fertilisation is now complete.
The egg maintains its ability to be fertilised for about 12 hours after ovulation. Sperm can remain viable in the cervical mucus for 48-72 hours or more around the time leading up to ovulation.
Implantation
The fertilised egg, now known as an embryo, develops in the fallopian tube for the first three days, then travels down into the uterus. By the fifth day it will become a blastocyst, a hollow ball of cells surrounding a cyst-like cavity.
Once the blastocyst breaks free from its shell, or hatches, it is ready to adhere to the surface of the endometrium. It begins to secrete human chorionic gonadotrophin (hCG), a hormone that tells the corpus luteum to continue progesterone production. A home pregnancy test will detect hCG by Day 28 of a menstrual cycle.
Intercourse timing
While sperm can survive for three of four days inside a woman, it only takes the egg between 12 and 24 hours to make its way through the fallopian tube after ovulation. The best chance of conception comes when a couple have intercourse one to two days before ovulation.
A woman typically ovulates 14 days before her period. If a woman has a regular cycle length of 28 days, she will ovulate mid-cycle - 14 days after day one of her period. If the cycle is longer, say 34 days, ovulation occurs around 20 days after day one of a period - not mid-cycle. Using this calculation will tell you when the best chance of conception will be.
Some women know when they are ovulating from changes in their body and the way they feel. Some typical indicators are breast soreness, heavier and more opaque vaginal discharge, tightness in the abdomen. Many others have no noticeable symptoms.
Basal body temperature (BBT)
Two days after ovulation, your temperature rises slightly. While this is not useful for that particular cycle, taking your temperature every morning before you get out of bed is an easy way to chart your cycle. Track the rises in BBT for a few months to work out how regular your cycle is and use this to predict the date of your ovulation.
If your tracking indicates that your cycle is irregular, try counting back 11 days from your longest cycle and 17 days from your shortest cycle. The days in between will be your most fertile.
Regular intercourse
Knowing that sperm can survive inside a woman for a number of days, if a couple is having regular sex (two to three times a week) there is a good chance that there will be some sperm there to meet your egg when it arrives.
It is a myth that men should "store" their sperm by abstaining from sex. Long periods of abstinence can lead to a decrease in sperm quality. Our best advice is to have sex two or three times a week, no matter where a woman is in her cycle.
Pregnancy & health
Both partners can benefit from a regime of healthy living.
For women:
Eat a well-balanced diet - A lack of essential nutrients can weaken the body and the immune system, so eat well and don't undertake any drastic diets. In particular, avoid foods high in Vitamin A, as large amounts may be harmful to the fetus; and increase your Vitamin D intake during pregnancy, as it is used to help the body absorb calcium.
Exercise in moderation - We recommend brisk walks, and exercises that strengthen the back, buttocks, abdominal and pelvic floor muscles. Avoid strenuous exercise following procedures, and don't exercise if it causes discomfort or your doctor advises against it.
Drink plenty of water - Aim for 10 to 12 glasses a day. Keep a water bottle handy and take regular sips throughout the day.
Avoid large amounts of caffeine - Try to limit yourself to two or three cups of coffee or tea per day. Remember that there is also caffeine in cola and chocolate.
Quit smoking - There are negative consequences of smoking for couples with low fertility. Drop this dangerous habit.
Reduce alcohol consumption - drinking to excess is harmful to both you and your fetus. No safe level of alcohol consumption has been decided for pregnancy, and many people prefer to avoid alcohol altogether. Be sure to avoid spirits, and don't drink more than two glasses of wine or beer at any one time. Read Prof Jansen's thoughts on alcohol and fertility.
Discuss any medication or nutritional supplements with your doctor - including over-the-counter drugs. Choose paracetamol for pain relief or fever, and avoid aspirin-based drugs as they may contribute to bleeding. Check with your doctor before you take antibiotics.
Protect yourself from infection - Make sure all meat, eggs and fish is well cooked. When reheating food, ensure it is heated through. Avoid unpasteurised foods including some soft cheeses, pâté, and products containing raw eggs (some mayonnaises). Wash fruit and salad. When gardening, wear gloves. Avoid animal waste in particular, contact with cat litter can cause an infection called toxoplasmosis. Wash hands after contact with animals.
Avoid chemicals - Stay away from paints, solvents, etc. Do not have your house fumigated while you are there.
Avoid overheating - Saunas and spas, while relaxing, can cause the body to overheat, which can be unhealthy.
Relax - a hobby or meditation class can be a real stress buster.
Take folic acid - it encourages healthy growth of cells in the first few weeks of pregnancy, reducing the incidence of neural tube birth defects such as spina bifida. We recommend you take two 500 mcg tablets per day for at least one month before embryo transfer and continue until at least the twelfth week of pregnancy.
For Men:
Pay attention to your diet and exercise habits - a man's sperm takes months to develop before ejaculation. Any bad habits that can affect sperm production can affect treatment for months.
Stay away from chemicals and environmental toxins - these can include paint, adhesives, printing inks and pesticides.
Quit smoking - tobacco and marijuana are particularly noxious to developing sperm. They should be avoided.
Check with your doctor before taking medications - Some drugs can also decrease or eliminate sperm production. Many of those commonly taken for high blood pressure or peptic ulcers can lower sperm count. Sulfasalazine, taken for colitis and anabolic steroids can temporarily cause complete absence of sperm. Chemotherapy drugs can permanently eliminate sperm production.
