4.3. Interpretation
The subgroup analysis between pregnant women with COVID-19 and nonpregnant people with COVID-19 showed that the incidences of fever and cough in pregnant women with COVID-19 (51%, 31%) were lower than that in ordinary people (91%, 67%), which may due to the changes in the immune system of pregnant women and further research is needed. A study from China CDC showed,80.9% of Chinese patients  were considered asymptomatic or mild pneumonia(25).Desmond Sutton et al. showed that of the 215 pregnant women who gave birth at the New York–Presbyterian Allen Hospital and Columbia University Irving Medical Center, 29 (87.9%) of the 33 patients who were positive for Sars-CoV-2 test had no symptoms of COVID-19 at the time of admission(19).The fact that the asymptomatic rate in the infected general population in China is lower than in infected pregnant women in the New York Medical Center seems to support this conclusion above. It suggested that Sars-CoV-2 test should be universal in high-risk areas to improve the isolation of asymptomatic infected individuals. It is different from the fact that pregnant women with SARS-CoV have worse prognosis than ordinary people with SARS- CoV(26). It is possible that in pregnant women, the clinical outcome of COVID-19 infection is better than that of SARS-CoV. Yan et al. confirmed that the current mortality rate of COVID-19(2%) is significantly lower than that of SARS (9.6%) , which may indicate that SARS is more pathogenic and lethal than COVID-19, thus pregnant women with COVID-19 infection had better outcomes than those with SARS-CoV(27). However, our finding that pregnancy women with COVID-19 had better clinical outcomes, might be biased owing to the relatively small sample included in this meta-analysis.
A meta-analysis showed that the CT positive rate of covid-19 infection in the general population was 89.76%(28), which was more than 71% in this paper. This also corresponded to the conclusion above that the clinical outcomes of pregnant women with COVID-19 were superior to general population. The incidence of positive CT findings was the highest among the symptoms. Shital J. Patel et al. confirmed that chest CT was considered a low-dose examination provided the fetus was excluded from the primary beam, and the estimated radiation doses were too low to induce fetal neurologic deficits during any trimester of pregnancy(29). It seemed that chest CT was suitable for routine screening of patients. However, there were a large quantity of pregnant women with asymptomatic infection (87.9%)(19). If chest CT is used as routine screening, it means that almost all pregnant women need it. In addition, WHO defines screening as the presumptive identification of unrecognized disease in an apparently healthy, asymptomatic population by means of tests, examinations or other procedures that can be applied rapidly and easily to the target population(30). As a consequence, it is improper to perform chest CT as a screening tool for pregnant women with COVID-19. We recommend to use it as the routine examination for suspected cases.
The rate of preterm labor in normal pregnant women worldwide is about 11% (31), which is lower than the result of this article (23%). The possible reason is that women in the third trimester of pregnancy terminate their pregnancy early after being infected with COVID-19 in order to proceed with further treatment. Most of these women choose early delivery by cesarean section in order to avoid prolonged labor which may worse COVID-19 for pregnant women(32)and increased risk of infection for medical staff(33). Chen R et al. confirmed that both epidural anesthesia and general anesthesia were safe and effective for women with COVID-19 during cesarean section (12).
Due to the P value was greater than 0.05, the rate of neonatal COVID-19 infection should not be considered. Wang S et al. reported the first case in China that the mother with COVID-19 gave birth to an infected baby in February 2, 2020 (34)and the instant SARS-CoV-2 nucleic acid tests of umbilical cord blood and placenta were both negative. And there are 3 neonates infected in the included literature. Khan S. et al reported that the swab samples tested within 24 hours after the delivery were positive in two neonates while intrauterine tissue samples such as placenta, cord blood or amniotic fluid were not tested (14). Yu N et al reported that the nucleic acid test for the throat swab of one neonate was positive at 36 h after birth (22). Without testing the intrauterine tissue samples, we could not confirm if the COVID-19 infection in the neonate was the result of intrauterine transmission. Two studies also showed that the test for SARS-CoV-2 specific antibodies (IgG and IgM) in neonatal serum samples could be evidence of vertical transmission (35, 36). Other literature revealed that almost all the other newborns from infected women were tested negative for SARS-CoV-2(10-13, 15-21, 23, 37-40). Wang C et al summarized that there was currently no evidence for intrauterine infection caused by vertical transmission in women with COVID-19 during the third trimester of pregnancy but it was uncertain whether there could be a risk of vertical transmission when the COVID-19 infection occurs in the first or second trimester, or when there was a long clinical manifestation-to-delivery interval (41). So we must continue to keep alert.