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CNN
05-05-2025
- Health
- CNN
Marijuana is extremely dangerous to the fetus in the womb, study finds
Source: CNN Using marijuana during pregnancy is linked to poor fetal development, low infant birth weight, dangerously early deliveries and even death, according to a new meta-analysis of research. 'The most striking finding is the increased risk of perinatal mortality — death either during the pregnancy or shortly after the pregnancy,' said obstetrician and lead study author Dr. Jamie Lo, an associate professor of obstetrics, gynecology and urology in the School of Medicine at Oregon Health & Science University in Portland. 'Prior work we've done shows prenatal cannabis use impacts fetal lung function and development, reducing the baby's lung volume,' Lo said. 'We've also found that there is significantly decreased blood flow and oxygen availability in the placenta. These are the likely underlying mechanisms driving some of our findings.' The placenta is a critical link between the mother and the developing fetus, delivering oxygen, nutrients and hormones necessary for growth. When that link is damaged, both the mother and the fetus are at risk. Despite the potential harms to the baby both before and after birth, use of marijuana during pregnancy is rising. A 2019 analysis of over 450,000 pregnant American women ages 12 to 44 by the National Institute on Drug Abuse found cannabis use more than doubled between 2002 and 2017. The majority of marijuana use occurred during the first three months of pregnancy, the study found, and it was predominantly recreational rather than medical. 'There is a mistaken perception that because marijuana is natural and plant-based, it's not harmful,' Lo said. 'I remind my patients that opium and heroin are also plant-based. Tobacco is a plant, and alcohol is also made from plants.' Using alcohol during pregnancy causes fetal alcohol syndrome. Smoking damages a fetus's developing lungs and brain — it is also a cause of SIDS, or sudden infant death syndrome, according to the US Centers for Disease Control and Prevention. Taking opioids, such as fentanyl, heroin or cocaine, are well-known causes of birth defects, poor fetal development and stillbirth, plus there's a high risk the baby will be born addicted and have to undergo withdrawal. These medical outcomes are known despite the lack of gold-standard clinical trials asking pregnant women to drink alcohol, smoke tobacco, take heroin, cocaine, oxycodone or fentanyl and then compare the outcomes to pregnant women who abstained. Such research, of course, would be grossly unethical. Thus, because a randomized clinical trial of the impact of cannabis on a fetus will never occur, scientists focus on the outcome of self-reported use by pregnant mothers. 'This systematic review is unique in that we only reviewed studies in which cannabis was used during pregnancy,' Lo said. 'Prior work has included studies which also looked at cannabis use along with other substances such as nicotine or alcohol.' The new research, published Monday in JAMA Pediatrics, analyzed 51 studies with over 21 million participants. Use of marijuana during pregnancy was linked to a 52% higher risk of preterm delivery before 37 weeks — full term is 40 weeks of gestation — and a 75% higher risk of low birth weight, which is less than 2,500 grams, or roughly 5.5 pounds at delivery, the study found. Only six studies looked at the impact of cannabis on mortality. Those studies found a 29% higher risk of infant death associated with the use of marijuana during pregnancy. The new meta-analysis used the GRADE (grading of recommendations assessment, development, and evaluation) approach to rating the quality of each study. In a prior analysis published in 2024, Lo and her team rated available studies as very low or low certainty, which means the evidence in the studies was limited and the findings not reliable. Just a year later, existing evidence was upgraded to low to moderate certainty. A moderate grade indicates researchers are reasonably confident in using that information for decision-making but recognize that future research might refine conclusions or recommendations. 'Research is evolving quickly in this area,' said Brianna Moore, assistant professor of epidemiology at the Colorado School of Public Health Anschutz Medical Campus in Aurora. She was not involved in the new study. 'This review found that as more studies are conducted with consistent results, there is more certainty that there is an association between prenatal exposure to cannabis and adverse birth outcomes,' Moore said in an email. In addition to believing that marijuana is safe because it's natural, expectant parents are also getting mixed messages about the health harms of cannabis. 'Perceptions of safety are compounded by the increased availability and legalization of cannabis,' Lo said. 'In addition, health care providers are poor at counseling due to confusion over conflicting studies. Therefore, there's no clear public health messaging. 'We're trying to change that by updating systematic reviews and producing peer-reviewed clinician briefs to help guide clinical counseling and management.' Historically it has been difficult to investigate cannabis use because weed has been illegal — and still is — in many states, while any studies that were undertaken had to follow strict federal regulations. Modern research into the potential harms of cannabis is still in its infancy. Older studies, often done in the 1980s when marijuana was much less potent, may not reflect today's reality, experts say. Research over the last decade has linked marijuana use to cognitive decline and dementia, complications during elective surgery, and an increased risk of some cancers. Weed users are nearly 25% more likely to need emergency care and hospitalization, according to a 2022 study. Any level of marijuana use may raise the risk of stroke by 42% and heart attack by 25%, even if there is no prior history of heart disease and the person has never smoked or vaped tobacco. Weed has also been linked to cardiac arrhythmias such as atrial fibrillation; myocarditis — an inflammation of the heart muscle — spasms of the heart's arteries and a higher risk of heart failure. Young people who use marijuana are more likely to develop long-lasting mental disorders, including depression, social anxiety and schizophrenia, and drop out of school, the CDC said. Studies show overuse of marijuana by youth with mood disorders leads to a rise in self-harm, suicide attempts and death. Daily use by adolescents and adults can result in another unpleasant side effect: uncontrollable vomiting, according to a 2021 study. And a 2020 study found children born to marijuana users had more psychotic-like behaviors and more attention, social and sleep problems, as well as weaker cognitive abilities. 'Ideally, it's best not to be exposed to THC, which is the psychoactive ingredient of cannabis, no matter what form you're using,' Lo said. See Full Web Article
Yahoo
05-05-2025
- Health
- Yahoo
Forget common folklore about the safety of weed. Marijuana harms babies, research shows
Using marijuana during pregnancy is linked to poor fetal development, low infant birth weight, dangerously early deliveries and even death, according to a new meta-analysis of research. 'The most striking finding is the increased risk of perinatal mortality — death either during the pregnancy or shortly after the pregnancy,' said obstetrician and lead study author Dr. Jamie Lo, an associate professor of obstetrics, gynecology and urology in the School of Medicine at Oregon Health & Science University in Portland. 'Prior work we've done shows prenatal cannabis use impacts fetal lung function and development, reducing the baby's lung volume,' Lo said. 'We've also found that there is significantly decreased blood flow and oxygen availability in the placenta. These are the likely underlying mechanisms driving some of our findings.' The placenta is a critical link between the mother and the developing fetus, delivering oxygen, nutrients and hormones necessary for growth. When that link is damaged, both the mother and the fetus are at risk. Despite the potential harms to the baby both before and after birth, use of marijuana during pregnancy is rising. A 2019 analysis of over 450,000 pregnant American women ages 12 to 44 by the National Institute on Drug Abuse found cannabis use more than doubled between 2002 and 2017. The majority of marijuana use occurred during the first three months of pregnancy, the study found, and it was predominantly recreational rather than medical. 'There is a mistaken perception that because marijuana is natural and plant-based, it's not harmful,' Lo said. 'I remind my patients that opium and heroin are also plant-based. Tobacco is a plant, and alcohol is also made from plants.' Using alcohol during pregnancy causes fetal alcohol syndrome. Smoking damages a fetus's developing lungs and brain — it is also a cause of SIDS, or sudden infant death syndrome, according to the US Centers for Disease Control and Prevention. Taking opioids, such as fentanyl, heroin or cocaine, are well-known causes of birth defects, poor fetal development and stillbirth, plus there's a high risk the baby will be born addicted and have to undergo withdrawal. These medical outcomes are known despite the lack of gold-standard clinical trials asking pregnant women to drink alcohol, smoke tobacco, take heroin, cocaine, oxycodone or fentanyl and then compare the outcomes to pregnant women who abstained. Such research, of course, would be grossly unethical. Thus, because a randomized clinical trial of the impact of cannabis on a fetus will never occur, scientists focus on the outcome of self-reported use by pregnant mothers. 'This systematic review is unique in that we only reviewed studies in which cannabis was used during pregnancy,' Lo said. 'Prior work has included studies which also looked at cannabis use along with other substances such as nicotine or alcohol.' The new research, published Monday in JAMA Pediatrics, analyzed 51 studies with over 21 million participants. Use of marijuana during pregnancy was linked to a 52% higher risk of preterm delivery before 37 weeks — full term is 40 weeks of gestation — and a 75% higher risk of low birth weight, which is less than 2,500 grams, or roughly 5.5 pounds at delivery, the study found. Only six studies looked at the impact of cannabis on mortality. Those studies found a 29% higher risk of infant death associated with the use of marijuana during pregnancy. The new meta-analysis used the GRADE (grading of recommendations assessment, development, and evaluation) approach to rating the quality of each study. In a prior analysis published in 2024, Lo and her team rated available studies as very low or low certainty, which means the evidence in the studies was limited and the findings not reliable. Just a year later, existing evidence was upgraded to low to moderate certainty. A moderate grade indicates researchers are reasonably confident in using that information for decision-making but recognize that future research might refine conclusions or recommendations. 'Research is evolving quickly in this area,' said Brianna Moore, assistant professor of epidemiology at the Colorado School of Public Health Anschutz Medical Campus in Aurora. She was not involved in the new study. 'This review found that as more studies are conducted with consistent results, there is more certainty that there is an association between prenatal exposure to cannabis and adverse birth outcomes,' Moore said in an email. In addition to believing that marijuana is safe because it's natural, expectant parents are also getting mixed messages about the health harms of cannabis. 'Perceptions of safety are compounded by the increased availability and legalization of cannabis,' Lo said. 'In addition, health care providers are poor at counseling due to confusion over conflicting studies. Therefore, there's no clear public health messaging. 'We're trying to change that by updating systematic reviews and producing peer-reviewed clinician briefs to help guide clinical counseling and management.' Historically it has been difficult to investigate cannabis use because weed has been illegal — and still is — in many states, while any studies that were undertaken had to follow strict federal regulations. Modern research into the potential harms of cannabis is still in its infancy. Older studies, often done in the 1980s when marijuana was much less potent, may not reflect today's reality, experts say. Research over the last decade has linked marijuana use to cognitive decline and dementia, complications during elective surgery, and an increased risk of some cancers. Weed users are nearly 25% more likely to need emergency care and hospitalization, according to a 2022 study. Any level of marijuana use may raise the risk of stroke by 42% and heart attack by 25%, even if there is no prior history of heart disease and the person has never smoked or vaped tobacco. Weed has also been linked to cardiac arrhythmias such as atrial fibrillation; myocarditis — an inflammation of the heart muscle — spasms of the heart's arteries and a higher risk of heart failure. Young people who use marijuana are more likely to develop long-lasting mental disorders, including depression, social anxiety and schizophrenia, and drop out of school, the CDC said. Studies show overuse of marijuana by youth with mood disorders leads to a rise in self-harm, suicide attempts and death. Daily use by adolescents and adults can result in another unpleasant side effect: uncontrollable vomiting, according to a 2021 study. And a 2020 study found children born to marijuana users had more psychotic-like behaviors and more attention, social and sleep problems, as well as weaker cognitive abilities. 'Ideally, it's best not to be exposed to THC, which is the psychoactive ingredient of cannabis, no matter what form you're using,' Lo said.
CNN
05-05-2025
- Health
- CNN
Forget common folklore about the safety of weed. Marijuana harms babies, research shows
Using marijuana during pregnancy is linked to poor fetal development, low infant birth weight, dangerously early deliveries and even death, according to a new meta-analysis of research. 'The most striking finding is the increased risk of perinatal mortality — death either during the pregnancy or shortly after the pregnancy,' said obstetrician and lead study author Dr. Jamie Lo, an associate professor of obstetrics, gynecology and urology in the School of Medicine at Oregon Health & Science University in Portland. 'Prior work we've done shows prenatal cannabis use impacts fetal lung function and development, reducing the baby's lung volume,' Lo said. 'We've also found that there is significantly decreased blood flow and oxygen availability in the placenta. These are the likely underlying mechanisms driving some of our findings.' The placenta is a critical link between the mother and the developing fetus, delivering oxygen, nutrients and hormones necessary for growth. When that link is damaged, both the mother and the fetus are at risk. Despite the potential harms to the baby both before and after birth, use of marijuana during pregnancy is rising. A 2019 analysis of over 450,000 pregnant American women ages 12 to 44 by the National Institute on Drug Abuse found cannabis use more than doubled between 2002 and 2017. The majority of marijuana use occurred during the first three months of pregnancy, the study found, and it was predominantly recreational rather than medical. 'There is a mistaken perception that because marijuana is natural and plant-based, it's not harmful,' Lo said. 'I remind my patients that opium and heroin are also plant-based. Tobacco is a plant, and alcohol is also made from plants.' Using alcohol during pregnancy causes fetal alcohol syndrome. Smoking damages a fetus's developing lungs and brain — it is also a cause of SIDS, or sudden infant death syndrome, according to the US Centers for Disease Control and Prevention. Taking opioids, such as fentanyl, heroin or cocaine, are well-known causes of birth defects, poor fetal development and stillbirth, plus there's a high risk the baby will be born addicted and have to undergo withdrawal. These medical outcomes are known despite the lack of gold-standard clinical trials asking pregnant women to drink alcohol, smoke tobacco, take heroin, cocaine, oxycodone or fentanyl and then compare the outcomes to pregnant women who abstained. Such research, of course, would be grossly unethical. Thus, because a randomized clinical trial of the impact of cannabis on a fetus will never occur, scientists focus on the outcome of self-reported use by pregnant mothers. 'This systematic review is unique in that we only reviewed studies in which cannabis was used during pregnancy,' Lo said. 'Prior work has included studies which also looked at cannabis use along with other substances such as nicotine or alcohol.' The new research, published Monday in JAMA Pediatrics, analyzed 51 studies with over 21 million participants. Use of marijuana during pregnancy was linked to a 52% higher risk of preterm delivery before 37 weeks — full term is 40 weeks of gestation — and a 75% higher risk of low birth weight, which is less than 2,500 grams, or roughly 5.5 pounds at delivery, the study found. Only six studies looked at the impact of cannabis on mortality. Those studies found a 29% higher risk of infant death associated with the use of marijuana during pregnancy. The new meta-analysis used the GRADE (grading of recommendations assessment, development, and evaluation) approach to rating the quality of each study. In a prior analysis published in 2024, Lo and her team rated available studies as very low or low certainty, which means the evidence in the studies was limited and the findings not reliable. Just a year later, existing evidence was upgraded to low to moderate certainty. A moderate grade indicates researchers are reasonably confident in using that information for decision-making but recognize that future research might refine conclusions or recommendations. 'Research is evolving quickly in this area,' said Brianna Moore, assistant professor of epidemiology at the Colorado School of Public Health Anschutz Medical Campus in Aurora. She was not involved in the new study. 'This review found that as more studies are conducted with consistent results, there is more certainty that there is an association between prenatal exposure to cannabis and adverse birth outcomes,' Moore said in an email. In addition to believing that marijuana is safe because it's natural, expectant parents are also getting mixed messages about the health harms of cannabis. 'Perceptions of safety are compounded by the increased availability and legalization of cannabis,' Lo said. 'In addition, health care providers are poor at counseling due to confusion over conflicting studies. Therefore, there's no clear public health messaging. 'We're trying to change that by updating systematic reviews and producing peer-reviewed clinician briefs to help guide clinical counseling and management.' Historically it has been difficult to investigate cannabis use because weed has been illegal — and still is — in many states, while any studies that were undertaken had to follow strict federal regulations. Modern research into the potential harms of cannabis is still in its infancy. Older studies, often done in the 1980s when marijuana was much less potent, may not reflect today's reality, experts say. Research over the last decade has linked marijuana use to cognitive decline and dementia, complications during elective surgery, and an increased risk of some cancers. Weed users are nearly 25% more likely to need emergency care and hospitalization, according to a 2022 study. Any level of marijuana use may raise the risk of stroke by 42% and heart attack by 25%, even if there is no prior history of heart disease and the person has never smoked or vaped tobacco. Weed has also been linked to cardiac arrhythmias such as atrial fibrillation; myocarditis — an inflammation of the heart muscle — spasms of the heart's arteries and a higher risk of heart failure. Young people who use marijuana are more likely to develop long-lasting mental disorders, including depression, social anxiety and schizophrenia, and drop out of school, the CDC said. Studies show overuse of marijuana by youth with mood disorders leads to a rise in self-harm, suicide attempts and death. Daily use by adolescents and adults can result in another unpleasant side effect: uncontrollable vomiting, according to a 2021 study. And a 2020 study found children born to marijuana users had more psychotic-like behaviors and more attention, social and sleep problems, as well as weaker cognitive abilities. 'Ideally, it's best not to be exposed to THC, which is the psychoactive ingredient of cannabis, no matter what form you're using,' Lo said.
CNN
05-05-2025
- Health
- CNN
Forget common folklore about the safety of weed. Marijuana harms babies, research shows
Using marijuana during pregnancy is linked to poor fetal development, low infant birth weight, dangerously early deliveries and even death, according to a new meta-analysis of research. 'The most striking finding is the increased risk of perinatal mortality — death either during the pregnancy or shortly after the pregnancy,' said obstetrician and lead study author Dr. Jamie Lo, an associate professor of obstetrics, gynecology and urology in the School of Medicine at Oregon Health & Science University in Portland. 'Prior work we've done shows prenatal cannabis use impacts fetal lung function and development, reducing the baby's lung volume,' Lo said. 'We've also found that there is significantly decreased blood flow and oxygen availability in the placenta. These are the likely underlying mechanisms driving some of our findings.' The placenta is a critical link between the mother and the developing fetus, delivering oxygen, nutrients and hormones necessary for growth. When that link is damaged, both the mother and the fetus are at risk. Despite the potential harms to the baby both before and after birth, use of marijuana during pregnancy is rising. A 2019 analysis of over 450,000 pregnant American women ages 12 to 44 by the National Institute on Drug Abuse found cannabis use more than doubled between 2002 and 2017. The majority of marijuana use occurred during the first three months of pregnancy, the study found, and it was predominantly recreational rather than medical. 'There is a mistaken perception that because marijuana is natural and plant-based, it's not harmful,' Lo said. 'I remind my patients that opium and heroin are also plant-based. Tobacco is a plant, and alcohol is also made from plants.' Using alcohol during pregnancy causes fetal alcohol syndrome. Smoking damages a fetus's developing lungs and brain — it is also a cause of SIDS, or sudden infant death syndrome, according to the US Centers for Disease Control and Prevention. Taking opioids, such as fentanyl, heroin or cocaine, are well-known causes of birth defects, poor fetal development and stillbirth, plus there's a high risk the baby will be born addicted and have to undergo withdrawal. These medical outcomes are known despite the lack of gold-standard clinical trials asking pregnant women to drink alcohol, smoke tobacco, take heroin, cocaine, oxycodone or fentanyl and then compare the outcomes to pregnant women who abstained. Such research, of course, would be grossly unethical. Thus, because a randomized clinical trial of the impact of cannabis on a fetus will never occur, scientists focus on the outcome of self-reported use by pregnant mothers. 'This systematic review is unique in that we only reviewed studies in which cannabis was used during pregnancy,' Lo said. 'Prior work has included studies which also looked at cannabis use along with other substances such as nicotine or alcohol.' The new research, published Monday in JAMA Pediatrics, analyzed 51 studies with over 21 million participants. Use of marijuana during pregnancy was linked to a 52% higher risk of preterm delivery before 37 weeks — full term is 40 weeks of gestation — and a 75% higher risk of low birth weight, which is less than 2,500 grams, or roughly 5.5 pounds at delivery, the study found. Only six studies looked at the impact of cannabis on mortality. Those studies found a 29% higher risk of infant death associated with the use of marijuana during pregnancy. The new meta-analysis used the GRADE (grading of recommendations assessment, development, and evaluation) approach to rating the quality of each study. In a prior analysis published in 2024, Lo and her team rated available studies as very low or low certainty, which means the evidence in the studies was limited and the findings not reliable. Just a year later, existing evidence was upgraded to low to moderate certainty. A moderate grade indicates researchers are reasonably confident in using that information for decision-making but recognize that future research might refine conclusions or recommendations. 'Research is evolving quickly in this area,' said Brianna Moore, assistant professor of epidemiology at the Colorado School of Public Health Anschutz Medical Campus in Aurora. She was not involved in the new study. 'This review found that as more studies are conducted with consistent results, there is more certainty that there is an association between prenatal exposure to cannabis and adverse birth outcomes,' Moore said in an email. In addition to believing that marijuana is safe because it's natural, expectant parents are also getting mixed messages about the health harms of cannabis. 'Perceptions of safety are compounded by the increased availability and legalization of cannabis,' Lo said. 'In addition, health care providers are poor at counseling due to confusion over conflicting studies. Therefore, there's no clear public health messaging. 'We're trying to change that by updating systematic reviews and producing peer-reviewed clinician briefs to help guide clinical counseling and management.' Historically it has been difficult to investigate cannabis use because weed has been illegal — and still is — in many states, while any studies that were undertaken had to follow strict federal regulations. Modern research into the potential harms of cannabis is still in its infancy. Older studies, often done in the 1980s when marijuana was much less potent, may not reflect today's reality, experts say. Research over the last decade has linked marijuana use to cognitive decline and dementia, complications during elective surgery, and an increased risk of some cancers. Weed users are nearly 25% more likely to need emergency care and hospitalization, according to a 2022 study. Any level of marijuana use may raise the risk of stroke by 42% and heart attack by 25%, even if there is no prior history of heart disease and the person has never smoked or vaped tobacco. Weed has also been linked to cardiac arrhythmias such as atrial fibrillation; myocarditis — an inflammation of the heart muscle — spasms of the heart's arteries and a higher risk of heart failure. Young people who use marijuana are more likely to develop long-lasting mental disorders, including depression, social anxiety and schizophrenia, and drop out of school, the CDC said. Studies show overuse of marijuana by youth with mood disorders leads to a rise in self-harm, suicide attempts and death. Daily use by adolescents and adults can result in another unpleasant side effect: uncontrollable vomiting, according to a 2021 study. And a 2020 study found children born to marijuana users had more psychotic-like behaviors and more attention, social and sleep problems, as well as weaker cognitive abilities. 'Ideally, it's best not to be exposed to THC, which is the psychoactive ingredient of cannabis, no matter what form you're using,' Lo said.
Daily Mail
29-04-2025
- Health
- Daily Mail
Scientists discover flu vaccine has disturbing effect on women's health
Getting a flu jab can disrupt women's menstrual cycles, scientists say. Experts found getting the vaccine, administered to millions of women each year, did result in a small change to menstrual cycle length. But the overall effect was minor, with an increase to cycle length of less than a day on average. They also found this occurred regardless of if women only got the flu vaccine or also got a Covid jab at the same time. During the initial rollout of the Covid vaccine tens of thousands of women complained about late or unusually heavy periods after getting jabbed. At the time anti-vaxx campaigners leapt on the reports, using them to peddle fears that vaccines may affect fertility, though these were soon dismissed by scientists. However, experts of the new study said it was critical to understand more about the phenomena and if it occurred in other jabs to help combat rising vaccine hesitancy. In the latest research, scientists from Oregon Health & Science University in US analysed data from just over 1,500 women aged between 18 and 45. Of these, 791 only had the flu vaccine and 710 had both it and the Covid jab. On average women who had the flu jab saw their menstrual cycle length increase by 0.4 days. This increased to an average of 0.49 days for women who got both jabs, a difference the authors said was negligible between the two groups. About one in 20 women in both groups did experience a change in cycle of at least eight days after vaccination. The authors also found that these changes to the menstrual cycle only occurred if women were vaccinated in the first half of their cycle. What's normal for a period? A period is the part of the cycle when a woman bleeds from her vagina for a few days. For most women this happens every 28 days or so but its not unusual for the cycle to be between 21 or 40 days for individual women. Periods tend to last between three and to eight days, with the average being five. Bleeding tends to be heaviest in the first two days. Some women have irregular periods where the cycle is inconsistent. For some this is natural and nothing to worry about, but the NHS advises women to contact their GP if: if their periods suddenly become irregular and they are under 45-years-of-age their periods come more often than every 21 days and less often than every 35 days their period lasts longer than seven days there is a difference of at least 20 days between the shortest and longest menstrual cycle Much like previous studies on the topic they found these changes were temporary. Writing in the journal JAMA Network Open they said their findings should help medics reassure patients worried about vaccine side effects, 'These findings may help clinicians confirm the utility of vaccination for patients with concerns about menstrual adverse effects of vaccination,' they said. They added the topic of how vaccines could influence the menstrual cycle had been neglected and it was important this was addressed. 'This provides an important first data point about how influenza vaccination might affect menstrual cyclicity, a topic that has been largely ignored throughout the almost century-long history of influenza vaccines,' they wrote. 'Public concern about new vaccines creates mistrust about all vaccines.' They said the exact mechanism of how vaccines caused changes in the cycle was unclear. However, they added the fact it only seemed to impact women in the first half of their cycle suggested the immune response generated by a jab affected a woman's production of hormones, leading to a disrupted cycle. The authors said women wanting to avoid these delays to their cycle may wish to time their vaccinations accordingly. They added that their study did have some limitations, notably their small and not very diverse sample size which could limit the findings. The length of the menstrual cycle varies between individual women, but the average is every 28 days. However, cycles as short as 21 days or as long as 40 are not considered unusual. The NHS advises women to contact their GP if their periods are irregular in certain situations. These include: if their periods suddenly become irregular and they are under 45-years-of-age, their periods come more often than every 21 days and less often than every 35 days, their period lasts longer than seven days, and there is a difference of at least 20 days between the shortest and longest menstrual cycle. Irregular periods can also lead to problems when women are trying to get pregnant as it becomes difficult to accurately track ovulation, the time when they are most likely to conceive.
