Making babies: a quick biology review

Trying to conceive? It seems like a simple equation: sperm plus egg equals baby. But it's not always as easy as it sounds. A variety of events must occur in just the right order to produce a pregnancy. Here's a quick review of baby-making biology.

The female side of the "equation"

In order to conceive, a woman must release an egg that can then be fertilized by the man's sperm. A woman's menstrual cycle is generally 28 days long, although some women have cycles that are longer or shorter than this. Day 1 is the first day of a woman's period. Sometime around Day 14 (for women with a 28-day cycle), she releases an egg from her ovaries - this is called ovulation. The egg travels down the fallopian tubes into her uterus, where it can then be fertilized. The process of ovulation is regulated by female hormones.

The male side of the "equation"

To father a child, a man must produce sufficient amounts of healthy sperm. Sperm are produced in a man's testes, pass through the epididymis, and are stored in the seminal vesicles.

The man must be able to deposit his sperm into the woman's vagina during intercourse. This usually happens during ejaculation. Then, the sperm must be able to swim well enough to reach the egg.

Sperm, meet egg.

To produce a pregnancy, the woman's egg must be fertilized by the man's sperm. The fertilized egg must then implant into the wall of her uterus, where it can begin to grow.

The secret to conceiving is proper timing. A woman's egg can live for up to 24 hours after it has been released. Sperm can survive inside a woman's body for a few days, and sometimes as long as 5 to 7 days. So, to maximize the chances of pregnancy, it is important to have intercourse around the time of ovulation (when the egg is released).

Women can calculate their ovulation time by tracking their menstrual periods. Ovulation usually occurs about 12 to 16 days before a woman's next period is expected. This method works best for women with regular cycles. But there are also other methods, including monitoring body temperature (which rises around the time of ovulation) and cervical mucus (which develops a slippery egg-white consistency around ovulation). Women can also use fertility monitors and ovulation kits to pinpoint the time of ovulation.

If you have any questions or concerns about fertility, speak to your doctor.

What is infertility and why does it happen?

With all the photos of movie stars sporting baby bumps well into their late 30s and even 40s, you might think that getting pregnant is easy. But often it's not. Up to 1 in 6 couples struggles with infertility.

Infertility is the inability to get pregnant after one year (or 6 months if the woman is 35 or over) of regular, unprotected intercourse. It is equally likely to be related to male factors (one-third of cases) or female factors (one-third of cases). The remaining one-third of cases is either unexplained, or caused by both female and male factors.

Factors that may contribute to infertility in men include:

  • problems with sperm (e.g., abnormally-shaped sperm, sperm that cannot swim properly, low sperm count): these may be caused by infections (such as mumps after puberty or sexually transmitted infections), age, medical conditions, or exposure to chemicals or high temperatures
  • abnormalities of the reproductive organs (such as undescended testes) or male hormone levels
  • erectile dysfunction (trouble getting an erection that is adequate for penetration)
  • retrograde ejaculation (a condition where semen moves into the bladder instead of out of the penis during ejaculation)

Factors that may contribute to infertility in women include:

  • problems with ovulation (releasing an egg from the ovaries)
  • damaged or blocked fallopian tubes
  • problems with cervical mucus (such as mucus that is too thick or mucus that contains sperm-killing antibodies)
  • endometriosis (a condition where uterus lining tissue is found outside of the uterus)
  • polycystic ovary syndrome (a hormonal imbalance that interferes with ovulation)
  • uterine fibroids (benign growths in the uterus wall)
  • scar tissue in or near the reproductive organs (may be caused by sexually transmitted infections, appendicitis, or surgery in the abdominal or pelvic area)
  • birth defects causing an abnormally-shaped uterus
  • early menopause

Other factors that can affect fertility (in both men and women):

  • age (both men's and women's fertility declines with age, although the decrease is more dramatic in women)
  • emotional stress (which can affect hormone levels)
  • poor nutrition
  • being overweight
  • exposure to toxic chemicals (such as lead and pesticides)
  • certain medications
  • smoking, drug use, or excessive alcohol intake
  • lubricant use
  • certain medical conditions (e.g., cancer, diabetes, thyroid problems)

Factors other than those listed may also play a role in infertility. If you are concerned about fertility, speak to your doctor to find out if any of these factors could be affecting your chances of conceiving.

Could you have a fertility problem?

If you are trying to conceive, you may be wondering how long it should take to get pregnant and how long you should wait before you get concerned about your fertility.

Unfortunately, there's no way to tell exactly how long it should take you to get pregnant. This varies from couple to couple, and depends on your age, your health, the type of birth control you were using before trying to conceive, and the timing of when you have intercourse.

In general, the chances of getting pregnant (after regular, unprotected intercourse) are:

  • 25% in the first month
  • 60% within 6 months
  • 75% within 9 months
  • 80% within 12 months
  • 90% within 18 months

These numbers are just a general guide, and may be lower for women over 30.

So how do you know when it might be time to worry? The main sign of infertility is an inability to get pregnant after 12 months of regular, unprotected intercourse (or 6 months for women 35 and over). However, you may wish to consult a doctor earlier if you have concerns about your fertility, especially if you or your partner may have any factors that could put you at risk of infertility (see "What is infertility and why does it happen?" to learn more).

To learn more about when to see a doctor and how to prepare for your visit, see "Seeking help for infertility."

Seeking help for infertility

A doctor can help couples with fertility concerns by offering tips on how to maximize fertility, diagnosing fertility problems, recommending a treatment plan for infertility, and counselling you on what to expect during the diagnosis and treatment process.

You should consider consulting a doctor if:

  • you are planning a pregnancy and have any concerns about fertility
  • you or your partner have one or more risk factors for infertility (see "What is infertility and why does it happen?")
  • you haven't been able to get pregnant after 12 months of regular, unprotected intercourse (for women under 35)
  • you haven't been able to get pregnant after 6 months of regular, unprotected intercourse (for women 35 and over)
  • you have had 3 or more miscarriages in a row

You may wish to consult your family doctor about your fertility first, or ask for a referral to a fertility specialist. You can also contact a fertility specialist directly.

To get the most out of your visit:

  • Before your visit, write down any questions you may have. See the questions below to help you get started.
  • Be prepared to discuss your partner's and your medical conditions and medications. Keep in mind that during the visit, your doctor may need to ask some questions about your sex life which may seem personal, but which are important to help get to the root of your fertility problem. Try to answer them honestly and provide as much detail as you can.
  • Bring a notepad and pen to your appointment to keep track of the information your doctor provides.

Questions to ask your doctor or fertility specialist:

  1. What do you think might be causing our fertility problem?
  2. What tests will you do to diagnose the problem?
  3. Will the tests be covered by my insurance?
  4. What treatment options are available? Which one do you recommend and why?
  5. How does the treatment work?
  6. What are the chances of success?
  7. Will the treatment be covered by my insurance?
  8. What will be involved in undergoing the treatment? How will it affect my life (e.g., the need for frequent injections and procedures, time off work)?
  9. What side effects should I watch for, and what should I do if they occur?
  10. How long should it take for the treatment to work?
  11. If this treatment does not work, what are our other options?
  12. What counselling options are available to help us cope with the emotional aspects of fertility treatment?