Evidence of possible SARS-CoV-2 vertical transmission according to World Health Organization criteria in asymptomatic pregnant women

Abstract

Objective: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vertical transmission has been investigated extensively. Recently, the World Health Organization (WHO) published strict criteria to classify the timing of mother-to-child transmission of SARS-CoV-2 into different categories. The aim of this study was to investigate the possibility of vertical transmission in asymptomatic SARS-CoV-2-positive women.

Methods: Pregnant women attending for delivery at a perinatology center in Mexico City, Mexico, who had a SARS-CoV-2-positive nasopharyngeal swab 24-48 h before delivery, were asymptomatic at the time of the test and had an obstetric indication for Cesarean section were eligible for inclusion in this study. Amniotic fluid was collected during Cesarean delivery, and neonatal oral and rectal swabs were collected at birth and at 24 h after birth. SARS-CoV-2 detection was carried out using real-time reverse-transcription polymerase chain reaction in all samples. Relevant medical information was retrieved from clinical records. The WHO criteria for classifying the timing of mother-to-child transmission of SARS-CoV-2 were applied to the study population.

Results: Forty-two SARS-CoV-2-positive asymptomatic pregnant women fulfilled the inclusion criteria. Twenty-five (59%) women developed mild disease after discharge. Neonatal death occurred in three (7%) cases, of which one had a positive SARS-CoV-2 test at birth and none had coronavirus disease 2019-related symptoms. There were five (12%) cases with strong evidence of intrauterine transmission of SARS-CoV-2, according to the WHO criteria, as amniotic fluid samples and neonatal samples at birth and at 24 h after birth were positive for SARS-CoV-2. Our results also showed that 40-60% of infected neonates would have been undetected if only one swab (oral or rectal) was tested.

Conclusion: This study contributes evidence to reinforce the potential for vertical transmission of SARS-CoV-2 even in asymptomatic women and highlights the importance of testing more than one neonatal sample in order to increase the detection rate of SARS-CoV-2 in affected cases. © 2021 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Keywords: COVID-19; SARS-CoV-2; newborn testing; pregnancy; vertical transmission.

Figure 1

Venn diagrams showing neonatal SARS‐CoV‐2 test results in asymptomatic SARS‐CoV‐2‐positive women. (a) Number of positive neonates at birth and at 24 h after birth. (b,c) Number of positive neonatal oral and rectal swabs at birth (b) and at 24 h after birth (c). *Including one case that did not undergo testing at 24 h.

Figure 2

Venn diagrams showing peripartum SARS‐CoV‐2 test results in asymptomatic SARS‐CoV‐2‐positive women, classified according to the World Health Organization criteria for mother‐to‐child SARS‐CoV‐2 transmission: (a) possible intrauterine transmission (n = 10); (b) unlikely intrauterine transmission or transient viremia (n = 7); and (c) intrapartum transmission (n = 5). AF, amniotic fluid.

Figure 3

Venn diagram showing peripartum SARS‐CoV‐2 test results and immunoglobulin G (IgG) detection in asymptomatic pregnant women classified according to the World Health Organization criteria for mother‐to‐child SARS‐CoV‐2 transmission as having possible intrauterine transmission (n = 10). Two neonates classified as having possible intrauterine transmission presented passive immunity specific for SARS‐CoV‐2. *Four out of 10 cases with positive maternal IgG had positive amniotic fluid (AF) and two out of six cases with positive neonatal IgG had positive AF, none of which was classified as having possible intrauterine transmission. For simplicity, these intersections are not shown.

Figure 4

Cycle threshold (Ct) values in asymptomatic SARS‐CoV‐2‐positive pregnant women, overall and in those with a positive neonate at birth and negative amniotic fluid (AF), those with positive AF and a negative neonate at birth, those with a positive neonate at birth and positive AF and those with a negative neonate at birth and negative AF. No significant differences were observed between the groups. Lines represent median and interquartile range.

Figure 5

Cycle threshold (Ct) values in SARS‐CoV‐2‐positive samples from asymptomatic pregnant women, their neonates at birth and at 24 h after birth, and amniotic fluid. The only statistically significant difference observed was between positive maternal samples and positive amniotic fluid samples (P = 0.005). Lines represent median and interquartile range.