8 How does a woman know she's pregnant?

8.1 Identifying the pregnacy

Our description of the developing embryo has, so to speak, detached it from its mother. But we should remember that on the other end of the placenta is a woman whose reaction to her pregnancy may lie almost anywhere in the scale of human emotion, and whose behaviour during her pregnancy will have an enormous effect on its outcome. This section attempts to look at the pregnancy from the mother's point of view. Of course, it cannot possibly be applicable to all women in all pregnancies – no text could ever do that – but it will attempt to draw out some general facts.

As you have seen above, much has been said throughout the ages about the beginning of pregnancy and the formation of a new individual. For most women, this is frankly irrelevant: fertilization and the first cell divisions pass unnoticed. The first sign of pregnancy for many women is a missed menstrual period, but this is by no means diagnostic. Women who have infrequent or irregular cycles may not be aware that they have missed one; even in women with regular cycles there are several reasons why a period might be missed.

Q Give some of these reasons.

A The woman may be undernourished, or ill, or breastfeeding, or be taking a lot of exercise.

Some women who are eager to become pregnant, and who are highly aware of their bodies, claim to ‘feel different’ only a few days after biologically successful intercourse. Just what these feelings consist of is difficult to ascertain, nor do they seem to be common to all women, but there is no doubt that they are real enough to the women concerned. Symptoms such as sore breasts and feeling bloated are certainly common in pregnancies, but do not usually become apparent until a couple of weeks after fertilization, a time when some women experience these symptoms anyway pre-menstrually. Conversely, women who either have no idea that they might be pregnant, or those who do not want to be, and unconsciously deny the possibility, can go for several months before finally realizing that they are in fact pregnant. Even symptoms such as nausea and vomiting, which some women find overwhelming, are often shrugged off as ‘a tummy bug’. So there is a significant emotional component in the recognition of pregnancy.

Whether or not a woman will welcome a pregnancy, it is often very important for her to know as early as possible whether a pregnancy has occurred. Pregnancy testing must surely have had a long history; it is related that some wise women could tell, apparently just by looking, whether a woman was pregnant. Indeed, even today there are mystics who claim that a woman's ‘aura’ changes when she is pregnant. If this is true, it might be related to the ‘different feelings’ that some women experience. However, these ‘tests’ cannot be substantiated by a scientific explanation, and other, more reproducible tests have been sought. One early favourite was the observation that if urine from a pregnant woman was rubbed on the back of a female toad, the toad would be induced to lay eggs. Urine from a non-pregnant woman would not do this. This was the pregnancy test of choice for many years, but it was not very accurate.

Q Can you suggest why not?

A If the toad was old or ill it might not be able to lay eggs. (On the other hand, if it was ready to spawn anyway, it might do so regardless of this external stimulus.)

The reason why pregnant women's urine can cause a toad to spawn is that it contains hormones which can penetrate the toad's skin and have the appropriate physiological effect in the toad's body. This led to the search for more accurate tests, and modern ones have got it down to a fine art.

Although many of the hormones in a woman's urine are present whether or not she is pregnant, there is one hormone that is absolutely diagnostic of pregnancy. It is called chorionic gonadotropin, and is made by trophoblast cells in the placenta, as you will see later. Currently available tests detect a very small amount of chorionic gonadotropin in urine, and so can be used very early in pregnancy – in fact, as soon as the placenta is formed, at around two weeks after fertilization. This time corresponds with the time a period would be expected if the woman were not pregnant, so can be used reliably as soon as the period is missed.