Low placental weight and altered metabolic scaling after severe acute respiratory syndrome coronavirus type 2 infection during pregnancy: a prospective multicentric study

Abstract

Objectives: A higher risk of adverse pregnancy outcomes is associated with SARS-CoV-2 infection; this could be partially explained by an altered placental function. Because histopathology is often unspecific, we aimed to assess placental weight, birthweight/placental weight (b/p) ratio, and the metabolic scaling exponent ß, an indicator of normal fetal-placental growth, to analyze placental function.

Methods: We included 153 singleton pregnancies with SARS-CoV-2-positive PCR result who delivered at three referring hospitals in Switzerland. Placental weight and b/p ratio were compared to published reference charts. Logistic regression analysis investigated the role of time of infection and other confounding factors on placental weight. The scaling exponent β was compared to the reference value of 0.75.

Results: Placental weight was inferior or equal to the tenth centile in 42.5% (65 of 153) and to the third centile in 19% (29 of 153) of the cases. The risk of low placental weight was not influenced by the trimester in which infection occurred. The b/p ratio was >50th centile in 80.4% (123 of 153) of the cases. The incidence of foetal growth restriction, preeclampsia, and gestational diabetes was 11.8% (18 of 153), 3.3% (5 of 153), and 19.6% (30 of 153). Linear regression modelling revealed a pathologic metabolic scaling exponent β of 0.871 ± 0.064 (R² = 0.56).

Discussion: SARS-CoV-2 infection during pregnancy was associated with a higher incidence of low placental weight, an increased b/p ratio, and an abnormal scaling exponent β in our cohort. This could be particularly relevant for the still controversial issue of an increased stillbirth rate in SARS-CoV-2 infection during pregnancy. In this regard, intensified foetal surveillance should be mandatory in these pregnancies.

Keywords: Birth weight/placental weight ratio; COVID-19; Metabolic scaling exponent β; Placental weight; SARS-CoV-2.

Fig. 1

Placental weights (black dots) plotted on reference ranges derived from Thompson et al. [19]. The lines represent the 10th, 50th, and 90th percentile for gestational age.

Fig. 2

Birthweight/placental weight ratio (b/p weight ratio). Placental weights (black dots) plotted on reference ranges derive from Thompson et al. [19]. The lines represent the 10th, 50th, and 90th percentile for gestational age.

Fig. 3

Relationship between birthweight and placental mass. Fitted straight line to natural logarithms (LN) of birthweight (BW) and placental weight (PW).