Your pregnancy and the “human” hormone

Hormones are a reality for all of us, female and male, adult and child, throughout the entirety of our lives, from our births until our sunset years. However, at no time in our existence – perhaps with the exceptions of the hormonal peaks of puberty and the hot flushes of menopause – do we feel the impact of hormones quite as keenly as we do during pregnancy.

In fact, hormones in pregnancy, particularly hCG, can be said to account for much of the actual experience of pregnancy and, in the early days, it is the hormone human chorionic gonadotropin which is responsible for those two tell-tale blue lines that form the basis of your pregnancy diagnosis.

Human chorionic gonadotropin

You could be forgiven for thinking that “human chorionic gonadotropin” sounds anything but human. However, it is in fact the major hormone produced by the cells which envelop the developing human embryo; the same cells which will eventually transform into the placenta.

There is a reason that human chorionic gonadotropin (or hCG) is used as the key component of pregnancy tests. The hormone begins to show up in urine, albeit at first in only small quantities, from around a week after fertilisation, and from then on doubles in detectable quantities every 2-3 days before peaking at week 6 in the pregnancy. Once at this stage the levels of human chorionic gonadotropin detectable in the bloodstream and urine will fall. However, it will remain detectable throughout the duration of the pregnancy.

By now you’ve probably also heard about another important pregnancy hormone: progesterone. What you may not know however is that progesterone production only made possible throughout the first trimester of pregnancy by human chorionic gonadotropin’s signalling to the corpus luteum (a temporary hormone producing structure essential to early pregnancy) that it should keep producing progesterone. Without this facility the womb would shed its lining, menstruation would take place and it would be impossible for the embryo to become successfully implanted.

But human chorionic gonadotropin is important in other ways too:

• It helps increase blood supply to the uterus
• It helps essential reshaping of the uterus
• It helps line the endometrium in readiness for the implantation of the embryo

Problems associated with human chorionic gonadotropin

There are few recorded cases of excessive levels of human chorionic gonadotropin during pregnancy and some evidence that significantly raised levels of the hormone may be a factor in the onset of molar pregnancies (a pre-cancerous condition affecting around 1 in 1,000 pregnancies in which the placenta and foetus do not form properly and the baby does not develop).

There are also some studies which show that raised levels of human chorionic gonadotropin are associated with a Down’s Syndrome pregnancy. However, the hormone does not cause Down’s; instead, it is thought that raised levels of the hormone are caused by an extra chromosome at position 21.

Significantly lower than normal levels of human chorionic gonadotropin may indicate a failing pregnancy and are not uncommon to ectopic pregnancies and miscarriages.

Blood testing for human chorionic gonadotropin

Although human chorionic gonadotropin is detectable in urine, a blood test provides more specific and more accurate information regarding the levels of the hormone in your body. The test is usually comprised of three sequential blood readings, taken 48hrs apart.

Doctors may request this if they are concerned you might be experiencing an ectopic pregnancy, are unsatisfied with the results of a scan or have doubts regarding the accuracy of a pregnancy test.

However, hCG levels will vary markedly between pregnant women, even those who are at the same stage in their pregnancy.

For instance a woman may have only 5 to 426 mlU (mili-international units) of hCG per ml of blood at four weeks from her last missed period (LMP), rising to 25,700 to 288,000 mlU/ml at nine to 12 weeks, then falling back again to 3,640 to 117,000mlU/ml at 25 weeks from LMP.

As such, diagnosis of an ectopic pregnancy requires a combination of blood tests, scan results, and individual medical history.