Researchers have found that changing the balance of two hormones could help in controlling the onset of labour in women, a major finding which they claim might prevent premature births.
"The trigger for the onset of labour in women has been a puzzle for a long time. Our findings show we have an answer, and furthermore may be able to delay or advance labour," lead author Roger Smith of John Hunter Hospital in Newcastle said.
Humans have two types of oestrogen -- estradiol (E2) and estriol (E3). When E2 and E3 are in roughly equal amounts there is no drive to labour, but the opposite holds true once one becomes in greater excess than the other.
In their study, the researchers evaluated the ratio of E3 to E2 in 500 pregnant women and found it went up rapidly as labour approached indicating that E3 could stimulate the onset of labour.
They then sought to understand what was causing the increase in E3 and they believe they found an answer.
In a previous study they showed that a hormone in the placenta, called corticotrophin-releasing hormone (CRH), rises rapidly through pregnancy, peaking at the time of labour. CRH levels rise earlier in women who deliver prematurely and later in women who deliver late, forming a biological clock which regulates the length of pregnancy.
The researchers also showed that CRH can act on the adrenal glands of the fetus to stimulate the production of a steroid hormone which the placenta uses to make E3.
This study showed a strong relationship between CRH levels in mother's blood in weeks before birth and levels of E3 supporting the view that CRH increases E3.
Smith said: "CRH may be the catalyst for the onset of labour, by driving steroid hormone production in the fetus, which then leads to an increase in E3 so that it exceeds E2.
"If this progression is correct, it may explain why women with a baby who dies in utero can still go into labour. In this scenario, levels of E3 would drop making E2 more dominant and triggering the onset of labour.
"It may be possible to delay or advance labor by varying the ratio of E3 to E2 by giving either E2 or E3 to the pregnant woman. It may also be possible to predict the timing of birth by monitoring this ratio between the two estrogens."
The findings are to be published in the 'Endocrine Society's Journal of Clinical Endocrinology & Metabolism'.
