Women may ovulate more than once a month

Dr Kirsty Horsey

Progress Educational Trust

12 July 2003

| | | |

[BioNews, London] Women may release eggs more than once during their monthly cycle, a new study by a group of Canadian researchers suggests. Their findings could lead to improvements in fertility treatments, and could also explain many unexpected pregnancies. 'We are in the early phases of understanding it, but it is quite a significant departure from what we all thought was going on for the last 50 years or so' said team leader Roger Pierson, of the University of Saskatchewan, Saskatoon.

The scientists carried out daily ultrasound scans on 63 women with normal menstrual cycles aged between 18-40, and studied their developing egg follicles over six weeks. It was previously thought that at the beginning of a normal ovarian cycle, around 15-20 follicles begin to grow, and that one mature egg is released, roughly halfway through the cycle. But the researchers found that in most of the women, follicle development occurred not just once, but in two or three 'waves' throughout the cycle. Although most ovulated once, between the 11th and 17th day, six of the women ovulated twice, and seven not at all. In the remaining 50 participants, 40 per cent had more than one wave of follicle activity, which could potentially have resulted in ovulation. 'We don't know why some waves lead to ovulation and others don't' said Pierson, although he speculated that luteinising hormone, which is produced following ovulation, could inhibit the release of another egg. He added that for couples with fertility problems, it might be possible to harness some of the non-ovulating waves into releasing eggs.

Pierson said the results, published in the journal Fertility and Sterility, also showed exactly why the rhythm method of contraception (relying on a 'safe' time of the monthly cycle to avoid pregnancy) doesn't work. They could also explain the occurrence of non-identical twins with different conception dates, and why some women undergoing fertility treatment may not respond to ovary-stimulating medicines. 'We're probably giving at least some of these women drugs at the wrong time' says Pierson. The group are now planning longer-term studies, to see if the women's patterns are consistent from month to month.

Reproduced with permission from BioNews, an email and online sources of news, information and comment on assisted reproduction and genetics.