Table 1 Baseline and pregnancy characteristics of the study participants.

Parameter	Multiple pregnancies (n = 165)	Singleton pregnancies (n = 5349)	P value
ART = assisted reproductive technology; BMI = body mass index Data are shown as mean ± standard deviation or absolute/relative frequencies (percentage). tt2 = Welch’s two-sample t-test; chi2 = Pearson’s chi-squared test
Maternal age (years)	32 ± 4.6	31 ± 5.3	0.005 tt2
Smoking (during pregnancy)	5/161 (3%)	209/5244 (4%)	0.57 chi2
BMI (kg/m 2 )	26 ± 5.3 (n = 155)	26 ± 5.6 (n = 5014)	0.05 tt2
ART in this pregnancy	47/143 (43%)	174/4861 (4%)
Maternal comorbidities (any)	65 (39%)	1919 (36%)	< 0.001 chi2
Cardiovascular comorbidities	6/163 (4%)	218/5295 (4%)	0.35 chi2
Diabetes mellitus (preexisting)	0/163 (0%)	54/5295 (1%)	0.78 chi2
Pulmonary comorbidities	5/163 (3%)	181/5295 (3%)	0.20 chi2
Coagulation disorder or state after thrombosis	1/163 (1%)	126/5295 (2%)	0.81 chi2
Vaccinated against SARS-CoV-2	59/154 (38%)	1550/5030 (31%)	0.14 chi2
Gestational age (week) at onset of COVID-19 symptoms	25 ± 8.8	27 ± 9.7
1 st Trimester	18 (11%)	545 (10%)	0.05 chi2
2 nd Trimester	77 (47%)	1933 (36%)	0.002 tt2
3 rd Trimester	70 (42%)	2871 (54%)	0.01 chi2