A recent spate of headlines about an “Ozempic baby boom” and reports of “surprise pregnancies” experienced by women who recently started taking weight loss drugs including semaglutide or liraglutide have led to questions about why this is happening, and whether there is any cause for concern. The drugs were never tested for use by women who were pregnant or hoping to become so, and some studies on Ozempic’s key ingredient, semaglutide, suggest an association with birth defects in animals.
The first part is easy to answer. The term used on social media to describe this phenomenon is “Ozempic babies”. But this is misleading: the truth of the matter is that these are not semaglutide babies, but weight loss babies. Despite the headlines, the medication itself has not done any magic to wake up the reproductive system – rather, it has caused weight loss and it is this that has restored ovulation.
We have known for a long time that there is a strong interaction between body weight and fertility, both for men and women. This means that both underweight and obesity can reduce the chances of fertility. The body understands that this is not the right time to embark on a pregnancy. We all have a specific range of body weight in which our fertility is optimal, and any weight outside this range can be problematic. From an evolutionary perspective this makes sense. If, for example, a woman is underweight, whatever the cause, then this means that she is unlikely to have enough stored nutrients for her foetus. Along the same lines, excessive adiposity – the condition of having much or too much fatty tissue in the body – can also increase the risk of something going wrong both for the mother and the baby during pregnancy. By “switching off” the reproductive system, the body is protecting the human species from a bad outcome.
The interaction between body weight regulation and the reproductive system is complex and fascinating.
The brain both controls body weight and orchestrates the reproductive system. The way that the brain senses energy stores is through a hormone called leptin which is produced from fat. Fat is a sophisticated organ that talks to the brain using leptin as a messenger. Low levels, as in the context of underweight, and high levels, as in the context of obesity, are sensed by the brain, which switches off the reproductive system. As a result, men either do not produce enough sperm or it is of low quality, while women stop ovulating and cannot conceive. Specifically in women, obesity can exacerbate another condition called polycystic ovarian syndrome which can reduce ovulation and the chance of conception.
There is some evidence from studies done in animals that the use of these medications upon conception can cause foetal malformations
Weight loss is a very effective way of improving the chances of fertility, mostly in women and less so in men. It is not clear yet how much weight women need to lose to start ovulating, but the number probably sits at about 5-10 per cent. This amount of weight loss can be achieved relatively rapidly and catch women off guard, sometimes leading to surprise pregnancies.
In the past, we’ve seen women after bariatric surgery conceiving even within weeks after their operation. My research group recently demonstrated this in the first randomised clinical trial in the field (Samarasinghe et al, Lancet 2024). Bariatric surgery kick-started ovulation in women with obesity and polycystic ovarian syndrome within four to eight weeks after the operation. This effect became more and more pronounced where the weight loss took place over the course of 12 months.
It should come as no surprise, then, that the same phenomenon happens in women taking weight loss medications to treat the disease of obesity, such as liraglutide and semaglutide.
Considering the popularity of medications for the disease of obesity, the question is whether such babies are healthy. The honest answer is that we do not really know yet.
There is some evidence from studies done in animals that the use of these medications upon conception can cause foetal malformations. Such studies have not been done in humans. Very similar to the use of any medication in women of child-bearing potential, such studies are rarely done so we may never get an answer from a high-quality study. However, national and international registries are being set up to collect information on what happens to the mother and baby during and after pregnancy.
While we are waiting to find out more about this issue, the advice to women using these medications is that they should be made aware of their effects on fertility and take appropriate birth control measures if they do not want a pregnancy.
But for women that are using these medication to increase their chances of having a baby this is obviously a lot more challenging. Weight loss is not only likely to increase their chance of conception, but also of a healthier pregnancy. But they will still need to stop the medication. And if they stop using the medication to reduce the theoretical risk of baby malformations, then they are likely to put weight back on and go back to square one.
The current recommendation is that women using these medications continue to use them, but stop for a few weeks or a couple of months before conception; this advice varies depending on the type of medication used, so women should consult with their doctor.
Dr Alexander Miras is Professor of endocrinology at Ulster University
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