The probability of conception - When is the best time to get pregnant?

Getting pregnant is, indeed, a bit like playing the lottery. You place your best bet and hope for the jackpot because conception and pregnancy do, in a way, still resemble a miracle. A lot of things have to happen for new life to come into being. Sperm have to be released and find their way through the vagina, the cervix, and into the uterus. There they have to meet the egg, which can only be fertilized in a very short period of time. And then the fertilized egg must divide, implant, divide further and grow into an embryo and later a fetus. All in all, less of a strategy game and more of a wheel of fortune. But what are the chances of getting pregnant?

After the egg is released into the fallopian tube, it can be fertilized for up to 24 hours. If ovulation has taken place, fertilization can only take place within this time window. This is why it is so important to be able to estimate the time of ovulation. Strictly speaking, a woman is only fertile at this time and this of course has a significant influence on the probability of conception. Under ideal conditions, sperm can survive in a woman’s body for up to five days. This extends the fertile window, which is limited to just 24 hours, to up to six days. This means that taking into account the viability of the sperm, the five days before ovulation and the day of ovulation (due to the viability of the egg) are defined as the woman’s fertile days. Unprotected intercourse during this time is significantly more likely to result in conception than on other days in the cycle. It is important to note that because ovulation is variable from cycle to cycle and from woman to woman (i.e. it does not always occur at the same time) and can occur early, in the middle or late in the cycle, unprotected intercourse can therefore theoretically lead to pregnancy throughout the cycle. Therefore, it’s very important to always consider the individual cycle of the respective woman in order to be able to accurately determine the probability of conception.

Does the famous ticking of the biological clock really exist? Well, let’s put it this way: if and when you can get pregnant in a cycle also depends on how old you are. 

Science actually agrees on this: the earlier you have children, the better. This applies to fertility as well as to the risk of genetic defects. The age between 20 and 30 is often described as the ideal time. But even in your early 30s, the probability of pregnancy is still at a good level. The risk of genetic defects is also hardly increased. From the age of 35, however, fertility decreases, and the risk of genetic defects increases as well. In addition, anovulatory cycles also occur more frequently. The sperm quality of the man also slowly decreases from the age of 35.

The probability of getting pregnant per cycle is about 25-30 % for women in their early 20s. From the age of 35, the probability is only about half as high. With advancing age, the probability decreases further. That means that it becomes more difficult to get pregnant, but that doesn’t mean it’s impossible. The ideal conditions are, of course, optimal health and fertility, as well as the correct determination of the fertile phase.

It is also important to note: in individual studies, different parameters were used to calculate the probability of conception, and their results therefore sometimes differ greatly. For example, in the studies with ovulation as the reference marker, the highest probability of conception is given as 33% on the day of ovulation (German database) and 36% two days before ovulation and on the day of ovulation (US database). In another American listing, the day before ovulation leads with 30%.
Ultimately, such statistical models are merely approximate values and the results are not intended to be disheartening or absolute. Nevertheless, they are interesting and provide a basis for further scientific debate.

We now know that the five days before ovulation and the day of ovulation (due to the viability of the egg) are defined as a woman’s fertile days. It is clear from research that the probability of becoming pregnant is very high during this period. The days with the maximum probability of conception are the two days before ovulation. It’s also important to be noted that studies on the probability of conception within the fertile window have tried to find figures to answer the question of the greatest probability of conception. Among other things, it could be shown that the duration of the fertile window in couples with average fertility is not constant at six days, but varies significantly interpersonally (in comparison with other couples) and intrapersonally (in relation to the respective couple, i.e. from cycle to cycle). In subfertile couples, the range of fluctuation is even greater and the fertility window is shorter compared to couples with higher fertility.

We know there are many myths and rumors out there about when in the cycle a woman definitely cannot get pregnant. For example, we always hear that women can’t get pregnant during menstruation. In reality, however, even though it is unlikely to get pregnant if you have sex during menstruation, it is definitely possible. Since every cycle and every woman is different, it is not possible to give one simple answer to this question. Here too, of course, the correct determination of the fertile window is of greatest importance. In any case, each woman and each cycle should be looked at individually. In addition, every woman should know her cycle well and consciously pay attention to her body’s signals.

As we now know, science defines 6 fertile days in a woman’s cycle: these consist of the 5 days of sperm viability plus the one day of egg viability. The probability of conception is highest during this period.

Although it is still widely believed, it is not correct to assume that ovulation always occurs in the middle of the cycle (or even in every cycle). To effectively increase the likelihood of conception and pregnancy, it is important to determine the entire fertile window. As you can imagine, this is not always easy, so there are definitely a few things you should know about accurately determining your fertile phase.

Well, the day of ovulation cannot be categorically fixed to one day of the cycle, but the timeframe of ovulation can be narrowed down as much as possible. Just as not every woman’s cycle is the same length every time, the time of ovulation can also shift. It can also happen that an egg does not mature in the ovaries in every cycle and therefore ovulation does not occur at all. If you wish to conceive, it is extremely important to observe each cycle individually in order to be able to make the best use of the entire fertile phase and to really effectively increase the chances of pregnancy.