Preconception series: Conception facts

Intercourse Timing

In a study of healthy women planning to become pregnant nearly all pregnancies were attributed to intercourse during a six day period ending on the day of ovulation. See Figure 1.

Figure 1: Probability of conception after a single act of intercourse in relation to ovulation

The ‘fertile window’ is important for couples to identify if they are trying to conceive. The length of this window relates to conception rates. Cervical mucus changes identify the ‘fertile window’ and if this is short (eg. 1 day as opposed to 4 days) there is less chance of conception. Mistiming intercourse may be a major reason for not conceiving. Monitoring your cervical mucus discharge is an effective way of identifying ovulation.

For more info see The Path to Pregnancy – Know your cycle

A couple is usually referred for investigation of subfertility after trying unsuccessfully to conceive for a year. Although many may despair of ever conceiving, the chance of successful spontaneous conception during the subsequent 3 years is about 50%. However, the chance is reduced if the woman has never been pregnant (primary subfertility) or is aged over 30, or the duration of subfertility is longer than 2 years.

Time to Conception

The chance of conceiving in one cycle is 20-25% in normal couples. After 6 cycles with intercourse in the fertile window, 80% of couples are expected to have conceived. After that, every second couple (10%) is probably seriously subfertile. However, of these couples who keep on trying after a year, nearly 55% will have a baby in the following 36 months. After 4 years 5% of the couples are definitely infertile with a nearly zero chance of becoming spontaneously pregnant in the future. 

It will take longer to conceive if you are:

• Over 35 years of age
• Overweight or obese (even if you have a normal menstrual cycle)
• Drink alcohol, even moderately (5 or less drinks per week)
• Smoke cigarettes
• Consume caffeine (3 or more cups of coffee per day)
• Are stressed
• Have irregular cycles or other reproductive problems (see Infertility)

Multiple Layer effect

Many lifestyle and health issues can have an impact on fertility and time to conception. Fertility is multi-faceted and there needn't be a major reproductive condition to affect fertility levels. Even minor problems, especially in combination, can cause the monthly chance of pregnancy to be much reduced. Therefore it is important that both prospective parents address as many health issues as possible to increase their fertility!