Many women are convinced that taking the pill makes them gain weight, but researchers have repeatedly failed to find a link.
But a new study suggests that some women are gaining weight while on the pill, and their genes are to blame.
Moreover, genes could explain why some women become pregnant even when taking the pill. This insight could ultimately lead to more ‘tailor-made’ contraception that works best for the individual woman.
Hormonal contraceptives, such as the pill, implants, and certain types of IUDs, work by preventing ovulation and thickening the mucus on the cervix (this blocks sperm from reaching an egg).
While many women are happy with their birth control, for some it is a hit and miss affair.
Many tolerate the side effects, including weight gain. A small minority becomes pregnant despite correct use of contraception.
Now, researchers at the Yale School of Medicine have discovered a link between weight gain and a common form of hormonal birth control that contains progestins. These are synthetic compounds that mimic progesterone, a hormone that suppresses ovulation.
They looked at 276 women who used implants containing etonogestrel, a progestin. Those who had a certain variant of the ESR1 gene were more likely to gain weight.
Hormonal contraceptives, such as the pill, implants, and certain types of IUDs, work by preventing ovulation and thickening the mucus on the cervix to prevent sperm from reaching an egg.
Aaron Lazorwitz, assistant professor of obstetrics, gynecology and reproductive sciences at Yale School of Medicine, discovered a link between weight gain and a common form of hormonal birth control
Aaron Lazorwitz, assistant professor of obstetrics, gynecology and reproductive sciences at Yale School of Medicine, who led the study, told Good Health: ‘This could indicate a biological process in which genetic differences place specific women at greater risk for weight gain. when using hormonal contraception.’
While it’s not clear why (one theory is that the genes change the way estrogen interacts with progesterone receptors), “we know that high levels of estrogenic activity appear to cause more weight-related problems compared to progestins,” he adds.
‘This could help explain why studies generally appear to show minimal weight change with hormonal contraception, as these genetic variants would only be found in a small proportion of women.’
In other words, although some women gain weight on the pill, many do not. Overall, the results of large studies therefore show little difference.
The discovery “holds great promise as a way to help predict a very unpleasant side effect for many women,” adds Dr. Lazorwitz.
Another important finding from the same Yale research team is that a mutation of another gene, CYP3A7, can increase the metabolism of etonogestrel, causing it to clear more quickly from the body before it has time to suppress ovulation.
About 5 percent of women carry this mutation and may be at greater risk for ‘contraceptive failure’ and pregnancy.
Although his research focused on implants, which are placed under the skin, Dr. Lazorwitz says etonogestrel works in the same way as other contraceptives, including the pill.
New technology could lead to more personalized contraception for women – reducing side effects, says Dr. Michelle Griffin, an obstetrician and gynecologist
“The hormones in pills and implants are metabolized in similar ways and have similar actions in the body, and therefore I expect the influence of genetic differences between the two to be similar,” he says.
Dr. Lazorwitz says his findings underline the need for a more personalized view of contraception – the current ‘trial-and-error’ approach can mean women typically try three or four methods before finding one that works for them, it found from a 2020 poll.
‘We currently have no means to predict an individual woman’s risks of contraceptive failure or side effects when selecting a contraceptive method, and I am hopeful that genetics will help us address this long-standing problem in women’s health care to solve,” he says.
New technology means it is possible to offer more personalized contraception for women – which in turn would lead to ‘fewer side effects and greater satisfaction’, adds Dr Michelle Griffin, an obstetrician and gynecologist and director of MFG Health Consulting, that advises women. healthcare companies.
Genetic testing for contraception is already available in the US, although nothing commercially exists yet to specifically test for the CYP3A7 mutation, says Dr. Lazorwitz. However, he says there is no reason why tests wouldn’t be available in the future to look for the CYP3A7 mutation alongside other genetic markers.
He adds that other genetic tests can also be useful – for example, to determine whether a woman carries a genetic variant that could put her at greater risk of blood clotting if she uses a hormonal contraceptive.
Dr. Griffin adds that while genetic testing is “very much in the research phase,” it could also help prevent the “blame mentality” often applied to women who become pregnant despite using contraception in the future: “I have had patients who reported that they took the contraceptive pill every day and still had an unintended pregnancy.’
The British Pregnancy Advisory Service (BPAS), an abortion care service, said that 51 percent of the 60,592 women it covered in 2016 (the most recent statistics) used at least one form of contraception when they became pregnant.
Each woman seeking contraception should be treated as a unique individual, says Dr. Ali Kubba, a gynecologist and contraceptive specialist based in London. This means patients need to be given a detailed lifestyle and sexual history, which can be a problem in busy NHS clinics, he adds.
He says gene testing alone may not be a solution because contraceptive failure can have several causes.
“An extreme example is Ozempic, which can sometimes cause vomiting, which affects the absorption of the oral contraceptive’s hormones,” he says. (Affected women should be offered non-oral contraceptive alternatives such as the patch, but this is infrequent, he adds.)
Dr. Kubba emphasizes that more research is needed on the links between genetics and weight gain associated with hormonal contraceptives.
“It’s important that we don’t place too much weight on one laboratory study (the Yale study),” he says.
More contraceptives are also needed to help men manage their fertility, says Heidi Stewart, chief executive of BPAS.
‘The more options people have to control their fertility and prevent unwanted pregnancies, the better.’