SARS-CoV-2 infection during pregnancy leads to low for gestational age placenta and elevated birthweight-placental weight ratio

ABSTRACT

Introduction A higher risk for adverse pregnancy outcome has been described in association with SARS-CoV-2 infection, which partially could be explained through alteration of the placental function. However, no significant placental damage in SARS-CoV-2-positive women could be found to date, as no histopathological 'footprint' in association with SARS-CoV-2 is yet available. Birthweight/placental weight ratio (b/p ratio), also defined as gram fetus per gram placenta, is a marker of placental efficiency. A high b/p ratio seems to be associated with adverse obstetrical outcome, revealing an increased nutrient transfer to the fetus, who despite its normal weight, seems to be at risk by 'outgrowing' its placenta. Given the inconsistency of data regarding placental histopathology, we decided for evaluation of the placental weight after SARS-CoV2 infection during pregnancy, by performing a case-control analysis. Methods We included in our study data originating from 153 women who suffered from SARS-CoV-2 infection during pregnancy and delivered since May 2020 at three large obstetrical centres in Switzerland. Placental weight was assessed in a standard manner. Placental weight and b/p ratio were compared to published reference charts (Thompson et al, BJOG 2007). Crude odds ratio (OR) was estimated using simple logistic regression depending on pregnancy trimester at diagnosis of SARS-CoV-2 infection. Results Placental weight was inferior or equal to the 10th centile in 42% (65/153) and inferior or equal to 3rd centile in 19% (29/153) of the cases. The risk of placental low weight was not significantly different between each trimester of infection. Multiparty was the only significant associated factor to the risk of low placental weight. Incidence of fetal growth restriction (FGR) was 11.6% (18/153), whereas presence of preeclampsia was noted in 0.03% of the cases (5/153). Gestational diabetes was present in 19.60% of the cases (30/153). B/p ratio was>50th centile in 80.4% of the cases and>90th centile in 31.37% of the cases. Discussions In our study, the absolute rate of low placentas weight was critically increased, leading to an elevated the b/p ratio, which raises concerns about the stability of the placental/fetal unity in these cases. The upregulated nutrient transfer capacity could be a sign that presumably low-risk fetuses are actually at high risk, and that SARS-CoV-2 could act as a 'promoter' for the destabilisation of the placental-fetal dyad in these pregnancies. Moreover, given the unexplained elevated GDM rate in our population, it remains open if this as well could be partially explained through an 'upregulation' attempt of the placenta, in order to provide more energy to the fetus at risk. This could be particularly relevant for the yet controversial issue of increased stillbirth rate in SARS-CoV-2 infection during pregnancy. In this regard, intensified fetal surveillance could be a reasonable option in these cases.