reproductive health

The use of hormonal contraceptives is associated with a small increase in the risk of breast cancer—one additional case of cancer for every 7,752 women who use these drugs—according to a Swedish study. The risk varies depending on the type of hormones administered, and is slightly higher with the use of contraceptives containing desogestrel. The study, published in JAMA Oncology, analyses data from a national registry between 2006 and 2019, with more than two million women aged between 13 and 49.

The decline in egg quality has been considered the main cause of declining fertility with age. A new study published in Science shows that the cells and tissues surrounding the oocytes within the human ovary also play a crucial role. They identified 11 types of cells in the ovaries, including nervous system cells, that influence follicle development. In addition, they have discovered that oocytes are grouped into “pockets” within the ovary and that the density within these pockets declines over the years. 

An international team has succeeded in generating fertilisable human eggs from skin cells using a novel technique. According to the authors, the study offers a way to address infertility, although they acknowledge that further research is needed to ensure efficacy and safety before future clinical applications. Of the 82 functional oocytes generated and fertilised, only 9% developed to day 6, when the experiment ended. In addition, the embryos had chromosomal abnormalities. The results are published in the journal Nature Communications.

Menstrual cycles were synchronised with lunar cycles until 2010, but according to research published in Science Advances, after this date, this synchrony is only found in January, when lunar gravity is at its strongest. The team analysed the menstrual records of 176 women and attributes the loss of synchrony to the increasing use of smartphones and LED night lights, which became widespread from 2010 onwards.

A Canadian team analysed samples from women undergoing in vitro fertilisation and found that higher concentrations of THC metabolites—the main psychoactive substance in cannabis—were associated with a higher rate of oocyte maturation and a lower number of embryos with the correct number of chromosomes. The latter could be replicated at similar concentrations under laboratory conditions. The authors, who published their findings in the journal Nature Communications, acknowledge that the study does not have sufficient statistical power to draw conclusions, but it does warn of possible risks to women's fertility.

In oocytes, mitochondrial DNA mutations do not increase with age in women, says a study published in Science Advances. The study detected mutations in different cells of 22 women between the ages of 20 and 42, and found that the mutations were more numerous in blood and saliva cells of older women, but not in their oocytes.

In 2015, the United Kingdom became the first country to pass legislation allowing the use of mitochondrial donation technology, pronuclear transfer. The technique is designed to limit, through in vitro fertilization, the transmission of mitochondrial DNA diseases in babies born to women who are at high risk, and for which there is no cure. Two studies published in the New England Journal of Medicine (NEJM) describe the results of the first treatments performed to date, from which eight babies have been born by mitochondrial donation, with reduced risk of disease.

A team in the United States has analysed how exposure to environmental chemicals in previous generations influences the onset of the first menstruation. The researchers used data from the California Child Health and Development Study (CHDS) and analysed blood samples taken from 250 pairs from the 1960s. The results, presented at the annual meeting of the Endocrine Society in San Francisco (USA), show that although the average age of first menstruation remained stable between grandmothers and their daughters, it decreased by one year between daughters and granddaughters. Certain chemicals present in the blood of the mother and father were linked to the onset of puberty in their descendants, with stronger effects in granddaughters, according to the study, and with greater weight of male exposure.

A research team from Murcia has found several types of microplastics in 69% of follicular fluid samples from 29 women and 55% of seminal fluid samples from 22 men, according to a presentation at the annual meeting of the European Society of Human Reproduction and Embryology (ESHRE), being held from 29 June to 2 July in Paris, France. The most frequent polymer in both types of samples was polytetrafluoroethylene (PTFE). The abstract of the research is published in the journal Human Reproduction.

Menstrual cycle tracking apps pose risks to users, according to a report published by the Minderoo Centre for Technology and Democracy at the University of Cambridge (United Kingdom). These apps collect intimate data about their users' physical and mental health and reproductive decisions, which can be exploited for commercial or legal purposes, the report warns.