Why is there a debate about miscarriage rates?

Modelled data causing yet more confusion

Over the years, pharmaceutical companies have kept hidden the dangerous effects of drugs like Thalidomide, Diethylstilbestrol, Primodos, and Valproate on pregnant women. They have covered up the harm caused by these drugs until it was too late. And now, it seems like history is repeating itself.

The miscarriage rates reported in studies conducted by pharmaceutical companies have been misrepresented for years. The true rate of baseline miscarriage is much lower than what these studies have led people to believe.

The covid vaccine data has exposed the misrepresentation of miscarriage rates. However, the US CDC has refused to publish the raw data from the publicly-funded V-SAFE pregnancy registry data. Despite this, available data from published studies confirms that the miscarriage rate is about double what it should be. 

In a study conducted by Zauche et al, it was found that women who received the covid vaccine had a miscarriage rate of 14.1%, which decreased to 12.8% after age standardisation. The researchers used modelling to arrive at this figure, as they had to take into account women who may have had a miscarriage before they received the vaccine. For instance, a pregnant woman who was vaccinated at 12 weeks had already passed the high-risk period for miscarriages, so women who would have presented at that time but had a miscarriage and were no longer pregnant had to be accounted for. Out of the 2,456 participants, 165 women miscarried after receiving the covid vaccine, which equates to 6.7% of the total. This number does not include women who miscarried before they would have been vaccinated. 

How many miscarriages is it reasonable to expect?

Calculating miscarriage rates is not an easy task. Most miscarriages occur between week 6 and week 10 of pregnancy. Miscarriages occurring after week 13 are uncommon, and they cannot occur beyond week 19, in US or 23 weeks in UK (beyond that date a pregnancy loss is registered as stillborn). There are three ways in which these rates can be calculated. 

  1. A simple raw percentage can be taken of the number of women who are registered as having miscarried out of total live pregnancies. This is around 5% for NHS data and for a huge study using US hospital data.
  1. Women who have presented as pregnant and have a confirmed ultrasound scan which shows a fetal heartbeat can be followed up to see how many go on to miscarry before 20 weeks. Naert et al did this study and concluded the figure was 5.4%.
  1. The final way is to use modelled data. All the women who see a doctor in each week of the first trimester are assumed to be representative of the whole population. Therefore if 10 out of 100 women who first see a doctor in week 8 of pregnancy see them because they are miscarrying then that percentage is extrapolated. The assumption made is that those pregnant women who are yet to register the pregnancy will miscarry at the same rate as those who see the doctor. The modelling is based on the flawed assumption that women who are miscarrying are as likely to see the doctor as women who have a healthy pregnancy. Such modelling was done by Zauche et al using methods published by Xu et al to reach a baseline miscarriage rate of 11-16%. They went a step further and assumed that the rate of miscarriage could also be extrapolated backwards such that rates measured in week 6 could be extrapolated backwards to week 5, 4 or even earlier – prior to conception! 

Rhongui Xu, a mathematician who devised the flawed model described above used a cancer survival model to analyse miscarriage data. Survival analysis caters for the time from the point at which you are diagnosed and adjusts for the length of time of follow-up, because in a cancer cohort you are getting people into your study at different times and so you have different lengths of time of follow-up. People die in cancer survival data, so the denominator (the number in the overall cohort) changes. The denominator for miscarriages should be the number of conceptions which is a constant. 

Given that the percentage of pregnant women who miscarried in the V-Safe database was higher than the baseline percentage this is a red flag. Modelling to account for miscarriages prior to vaccination can only make that percentage higher.

Any increase in miscarriage rate will be predominantly confined to those who have received the drug in the 6-8 week window. Yet repeatedly, people hide the signal by including every trimester in the denominator.

A recent paper has also demonstrated that animal studies show a higher rate of fetal loss when the mother was injected with lipid nanoparticles rather than saline. The paper was trying to find a lipid nanoparticle that would target the placenta but these particles are not silver bullets all the ones tested accumulated in the placenta.

The recent revelations surrounding misrepresented miscarriage rates by the pharmaceutical industry underscore the importance of transparency and rigorous oversight. As the covid vaccine data sheds new light on this critical issue, it is imperative that we continue to scrutinise research practices and hold both pharmaceutical companies and regulatory agencies accountable. By doing so, we can safeguard public health and ensure that pregnant women receive accurate information to make informed decisions about their healthcare.

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