The Truth About Hormones

Women are much better at judging social situations and are more sensitive to facial expressions than men. They worry about how other people are feeling, putting themselves in their shoes (empathizing) and are keen to chat and share intimacy. Men are better at working out how things work (systemizing), be it washing machines, computer programs or armies; they prefer games and gadgets. They may start collecting things – football stats, CDs, beer mats – a hobby which is often a complete mystery to women. At the same time the appeal of watching soaps on TV and the concept of shopping for pleasure is mystifying men. Most men will run a mile before they do the ‘talking about problems’ thing.

The researchers found that the higher the levels of pre-natal testosterone in the amniotic fluid, the less eye contact the toddlers made, and the smaller their vocabulary. These toddlers were seen again when they were four years old. By this time, those children that had had the highest level of prenatal testoerone had lower social skills and more restricted interests than those who had had lower levels of testosterone in their bath of amniotic fluid.

Fetal testosterone clearly affects the brain in some way and therefore influences behaviour for the rest of the baby’s life. In a nutshell, the more you have in the womb, the more of a systemizer you are; the less you have, the more of an empathizer you are. While of course baby boys produce more testosterone, baby girls also produce it, some almost to the levels of the least producing boys.

The mechanism that turns the embryo’s genetic sex into the adult male or female depends on an immensely complex interplay of genetic, psychological, social and, naturally, hormonal factors. The chief hormonal factor is the influence of testosterone in the womb.

Pregnancy is hormone-driven and hormone-maintained; birth is hormone-initiated, as is lactation. Having a baby means that for the best part of a year, hormones are in complete control of your life and that of your baby. So it’s hardly surprising that women complain that they feel ‘hormonal’ during pregnancy. Their bodies are exposed to industrial levels of steroids, principally oestrogen and progesterone. Women on average experience a peak progesterone level of 30 mg per twenty-four hours during their menstrual cycles. During pregnancy, that rises to 75 mg per twenty-four hours at twenty weeks and a walloping 300 mg by forty weeks. Oestrogen levels soar not just tenfold but a hundredfold. One of the oestrogens – oestradiol – increases a thousandfold. This tidal wave of hormones also engulfs the baby

This fits closely with the Barker hypothesis, developed by David Barker and his colleagues at Southampton University, which says that adult health is programmed by conditions in the womb. The more a baby is stressed (this also includes things like poor nutrition, poor blood flow) during pregnancy, the more likely he or she is to develop problems such as cardiovascular disease or diabetes in later life. Damping down the mother’s stress response means that programming isn’t triggered unless it’s really necessary.

How does the baby produce these steroids? The developing baby’s adrenal glands are larger than its kidneys. Even after birth they are still relatively large – about twenty times their relative size in an adult – and so have to undergo a period of downsizing until they are the ‘right’ size. One of their chief functions during fetal life, however, is to semi-assemble steroid hormones before passing them over to the placenta where the manufacturing into fully fledged oestrogens takes place. Roughly ten times more steroids go from baby to mother than the other way round. Passing incomplete steroids over to the mother is cunning because it means that the baby is protected from the harmful effects of the steroids

Deficiency or excess of insulin, however, is a totally different matter. Diabetic women whose insulin is poorly controlled in pregnancy can have very large babies – 4.5 kg (nearly 10lb) and more, compared to the British average of 3.3 kg (7lb 2oz). This is called macrosomia. Too little insulin, on the other hand, and the babies do not grow properly.

For instance, vigorous exercise during pregnancy raises testosterone levels, although sustained exercise, such as a long run, lowers testosterone. If a woman is under a great deal of stress during pregnancy, as a result, for example, of bereavement or war, testosterone levels are increased.

The presence of hCG in the urine is the basis of pregnancy tests. Today, you can buy pregnancy test kits at any chemist. They are simple to use, accurate and the results are available within ten minutes. Essentially the tests use a sniffer dog approach, and search for that little beta chain section of hCG.

The default gender in the womb is female, which is perhaps hardly surprising given that the womb is an environment awash with female hormones. A genetically male fetus will therefore develop the female form of sexual organs until ‘maleness’ is switched on by the SRY gene on the Y chromosome, and the fetal testis starts to develop and then produce testosterone. Incidentally a functioning ovary is not needed to appear to be female, whereas a functioning testis is essential for a man.