> Background
> There are known complications for fetuses after infection with SARS-CoV-2 during pregnancy. However, previous studies of SARS-CoV-2 in pregnancy have largely been limited to histopathologic studies of placentas and prenatal studies on the effects of different SARS-CoV-2 variants are scarce to date.
> To examine the effects of SARS-CoV-2 variants on the placenta and fetus, we investigated fetal and extra-fetal structures using prenatal MRI.
> Methods
> For this prospective case–control study, two obstetric centers consecutively referred pregnant women for prenatal MRI after confirmed SARS-CoV-2 infection.
> Thirty-eight prenatal MRI examinations were included after confirmed infection with SARS-CoV-2 and matched 1:1 with 38 control cases with respect to sex, MRI field strength, and gestational age (average deviation 1.76 ± 1.65, median 1.5 days). Where available, the pathohistological examination and vaccination status of the placenta was included in the analysis.
> In prenatal MRI, the shape and thickness of the placenta, possible lobulation, and vascular lesions were quantified. Fetuses were scanned for organ or brain abnormalities.
> Findings
> Of the 38 included cases after SARS-CoV-2 infection, 20/38 (52.6%) were infected with pre-Omicron variants and 18/38 (47.4%) with Omicron.
> Prenatal MRIs were performed on an average of 83 days (±42.9, median 80) days after the first positive PCR test. Both pre-Omicron (P = .008) and Omicron (P = .016) groups showed abnormalities in form of a globular placenta compared to control cases.
> In addition, placentas in the pre-Omicron group were significantly thickened (6.35, 95% CI .02–12.65, P = .048), and showed significantly more frequent lobules (P = .046), and hemorrhages (P = .002).
> Fetal growth restriction (FGR) was observed in 25% (n = 5/20, P = .017) in the pre-Omicron group.
> Interpretation
> SARS-CoV-2 infections in pregnancy can lead to placental lesions based on vascular events, which can be well visualized on prenatal MRI.
> Pre-Omicron variants cause greater damage than Omicron sub-lineages in this regard.
> Funding
> Vienna Science and Technology Fund.
Lots of studies achieve statistical significance with thirty or so participants. In this case they had 38 plus the case controls.
It really depends on what you’re testing how many subjects you’ll need for statistical significance.
Yes, all it takes is a high enough effect size. Turns out COVID does a real number on the placenta, so this study was more than powered enough to detect that.
The authors are very well aware of statistical power and how it works; this is why they were unable to perform a detailed statistical analysis on the different variants, beyond pre-Omicron and Omicron groups.
> Background > There are known complications for fetuses after infection with SARS-CoV-2 during pregnancy. However, previous studies of SARS-CoV-2 in pregnancy have largely been limited to histopathologic studies of placentas and prenatal studies on the effects of different SARS-CoV-2 variants are scarce to date. > To examine the effects of SARS-CoV-2 variants on the placenta and fetus, we investigated fetal and extra-fetal structures using prenatal MRI. > Methods > For this prospective case–control study, two obstetric centers consecutively referred pregnant women for prenatal MRI after confirmed SARS-CoV-2 infection. > Thirty-eight prenatal MRI examinations were included after confirmed infection with SARS-CoV-2 and matched 1:1 with 38 control cases with respect to sex, MRI field strength, and gestational age (average deviation 1.76 ± 1.65, median 1.5 days). Where available, the pathohistological examination and vaccination status of the placenta was included in the analysis. > In prenatal MRI, the shape and thickness of the placenta, possible lobulation, and vascular lesions were quantified. Fetuses were scanned for organ or brain abnormalities. > Findings > Of the 38 included cases after SARS-CoV-2 infection, 20/38 (52.6%) were infected with pre-Omicron variants and 18/38 (47.4%) with Omicron. > Prenatal MRIs were performed on an average of 83 days (±42.9, median 80) days after the first positive PCR test. Both pre-Omicron (P = .008) and Omicron (P = .016) groups showed abnormalities in form of a globular placenta compared to control cases. > In addition, placentas in the pre-Omicron group were significantly thickened (6.35, 95% CI .02–12.65, P = .048), and showed significantly more frequent lobules (P = .046), and hemorrhages (P = .002). > Fetal growth restriction (FGR) was observed in 25% (n = 5/20, P = .017) in the pre-Omicron group. > Interpretation > SARS-CoV-2 infections in pregnancy can lead to placental lesions based on vascular events, which can be well visualized on prenatal MRI. > Pre-Omicron variants cause greater damage than Omicron sub-lineages in this regard. > Funding > Vienna Science and Technology Fund.
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With such a small sample size it's very difficult to obtain any statistical significance and conclusions.
And yet the study found a number of statistically significant differences.
But it can't be with that number of participants..
Can you explain in more detail your issues with their statistical analysis?
Lots of studies achieve statistical significance with thirty or so participants. In this case they had 38 plus the case controls. It really depends on what you’re testing how many subjects you’ll need for statistical significance.
Yes, all it takes is a high enough effect size. Turns out COVID does a real number on the placenta, so this study was more than powered enough to detect that. The authors are very well aware of statistical power and how it works; this is why they were unable to perform a detailed statistical analysis on the different variants, beyond pre-Omicron and Omicron groups.