Study findings updated . AI-assisted evidence summary, not individual medical advice or a clinician endorsement.
THE SHORT VERSION
What’s worth knowing.
The key findings, what they mean, and the context that matters.
THE HEADLINE TAKEAWAY1.9× stillbirth riskAdjusted relative risk, US deliveries with vs without COVID, 2020–2021
Stillbirth was nearly twice as common when mothers had COVID at delivery.
In a large US hospital database, 1.26% of deliveries with COVID recorded during the delivery stay ended in stillbirth (a baby dying before birth), versus 0.64% of deliveries without COVID. During the Delta wave, the gap widened to 2.70% versus 0.63%.
Stillbirth stayed rare, but COVID around delivery was tied to a clear rise in it. The link was strongest when the Delta variant dominated, before most pregnant women were vaccinated. Hospital billing records show a link, not proof of cause, and a later analysis of the same US database found no clear rise in stillbirth during the Omicron waves.
See the evidence
A CDC analysis of 1,249,634 deliveries at 736 US hospitals from March 2020 to September 2021, using hospital billing records.
From the study: “affecting 0.64% and 1.26% of deliveries without COVID-19 and with COVID-19, respectively (aRR = 1.90; 95% CI = 1.69–2.15)”
1.9× stillbirth risk
DeSisto CL et al. Risk for Stillbirth Among Women With and Without COVID-19 at Delivery Hospitalization - United States, March 2020-September 2021. MMWR. Morbidity and mortality weekly report. 2021.
From the study: “During the Delta period (July–September 2021), 1,171 stillbirths were documented, involving 2.70% of deliveries with COVID-19 compared with 0.63% of deliveries without COVID-19”
1.9× stillbirth risk
DeSisto CL et al. Risk for Stillbirth Among Women With and Without COVID-19 at Delivery Hospitalization - United States, March 2020-September 2021. MMWR. Morbidity and mortality weekly report. 2021.
Vaccination during pregnancy helped keep young babies out of the hospital.
52% protectionAgainst COVID hospitalization in babies under 6 months, via mothers' mRNA shots
Comparing US babies hospitalized with COVID to babies hospitalized for other reasons, a complete mRNA series during pregnancy gave 52% protection against COVID hospitalization and 70% against intensive care. Protection was 80% during Delta but 38% during Omicron.
Babies under 6 months cannot get COVID vaccines themselves, so antibodies passed from mother across the placenta are an important shield. Protection was higher when mothers were vaccinated after 20 weeks. An observational test-negative study, not a randomized trial, and protection against Omicron was much lower and less certain than against Delta.
See the evidence
A CDC-funded case-control study of 537 babies hospitalized with COVID and 512 without, at 30 hospitals in 22 states, July 2021 to March 2022.
From the study: “The effectiveness of maternal vaccination against hospitalization for Covid-19 among infants was 52%”
52% protection
Halasa NB et al. Maternal Vaccination and Risk of Hospitalization for Covid-19 among Infants. The New England journal of medicine. 2022.
From the study: “Effectiveness was 80% (95% CI, 60 to 90) during the period of delta predominance, as compared with 38% (95% CI, 8 to 58) during the period of omicron predominance.”
52% protection
Halasa NB et al. Maternal Vaccination and Risk of Hospitalization for Covid-19 among Infants. The New England journal of medicine. 2022.
US pregnancy-related deaths rose sharply in 2021, alongside COVID deaths.
45.5 deaths per 100,000Per 100,000 US live births in 2021, up from 29.0 before the pandemic
Deaths during pregnancy or in the year after, from pregnancy-related causes, reached 45.5 per 100,000 US live births in 2021, compared with 29.0 before the pandemic. American Indian and Alaska Native people were hit hardest, at 160.8 per 100,000 in 2021 versus 79.0 in April to December 2020.
The jump tracked rising COVID deaths among women of childbearing age and widened existing racial gaps, showing how deeply the pandemic reached into maternal health in the United States. National death-certificate data show a trend over time, not proof that COVID caused each death, and cause-of-death coding on certificates can be imperfect.
See the evidence
An analysis of CDC WONDER national death and birth records from 2019 through 2021, comparing pregnancy-related death rates before and during the pandemic.
From the study: “Pregnancy-related mortality was significantly higher in 2021 (45.5/100,000 live births)”
45.5 deaths per 100,000
Thoma ME et al. Changes in Pregnancy-Related Mortality Associated With the Coronavirus Disease 2019 (COVID-19) Pandemic in the United States. Obstetrics and gynecology. 2023.
From the study: “and before the pandemic (29.0/100,000 live births)”
45.5 deaths per 100,000
Thoma ME et al. Changes in Pregnancy-Related Mortality Associated With the Coronavirus Disease 2019 (COVID-19) Pandemic in the United States. Obstetrics and gynecology. 2023.
From the study: “American Indian/Alaska Native people during 2021 compared with April-December of 2020 (pregnancy-related mortality ratio 160.8 vs 79.0/100,000 live births”
45.5 deaths per 100,000
Thoma ME et al. Changes in Pregnancy-Related Mortality Associated With the Coronavirus Disease 2019 (COVID-19) Pandemic in the United States. Obstetrics and gynecology. 2023.
Preterm birth risk spikes in the two weeks after COVID in pregnancy.
14 days of highest riskPreterm birth risk peaked in the 2 weeks after a positive COVID test, Sweden
In Swedish national data, pregnant women's risk of giving birth too early was highest in the 14 days after a positive COVID test. Compared with uninfected women, infected women had 3.2 times the hazard (rate over time) of preterm birth if unvaccinated, but 1.6 times if vaccinated before infection.
A defined window gives women and clinicians a warning period: the authors urge counselling on early labor signs so care is sought without delay. Vaccination before infection was linked to a lower risk. A registry study of positive tests only, so untested mild infections were missed, and it shows links rather than proof that infection or vaccination changed the risk.
See the evidence
A Swedish nationwide register study of 233,335 singleton pregnancies due between March 2020 and May 2022.
From the study: “Pregnant women are at particularly high risk of PTB within 14 days after a SARS-CoV-2 infection”
14 days of highest risk
Berglin, Lisa et al.. Severe acute respiratory syndrome coronavirus 2 and preterm birth, clinical implications-A register-based cohort study from Sweden.. Pregnancy (Hoboken, N.J.). 2025. [Source notice: Correction 2026-01-12 (10.1002/pmf2.70206) replaced the initial 25% infection sample with the full population and corrected numerical content and figures. The vaccination finding is withheld because the current abstract and Results disagree on its confidence interval.]
From the study: “The aHR for preterm birth among vaccinated infected women compared to non-infected was 1.6”
14 days of highest risk
Berglin, Lisa et al.. Severe acute respiratory syndrome coronavirus 2 and preterm birth, clinical implications-A register-based cohort study from Sweden.. Pregnancy (Hoboken, N.J.). 2025. [Source notice: Correction 2026-01-12 (10.1002/pmf2.70206) replaced the initial 25% infection sample with the full population and corrected numerical content and figures. The vaccination finding is withheld because the current abstract and Results disagree on its confidence interval.]
From the study: “The corresponding aHR for women who had a SARS-CoV-2 infection without a previous vaccination was 3.2”
14 days of highest risk
Berglin, Lisa et al.. Severe acute respiratory syndrome coronavirus 2 and preterm birth, clinical implications-A register-based cohort study from Sweden.. Pregnancy (Hoboken, N.J.). 2025. [Source notice: Correction 2026-01-12 (10.1002/pmf2.70206) replaced the initial 25% infection sample with the full population and corrected numerical content and figures. The vaccination finding is withheld because the current abstract and Results disagree on its confidence interval.]
COVID vaccination in pregnancy was not linked to more preterm births.
No added preterm riskOntario births after COVID vaccination in pregnancy vs no vaccination in pregnancy
Among Ontario births, preterm birth occurred in 6.5% of those vaccinated against COVID during pregnancy versus 6.9% of those unvaccinated in pregnancy, with no added risk after adjustment. Stillbirth was 0.25% versus 0.44%, and babies small for their age 9.1% versus 9.2%.
Fear of harming the baby kept many pregnant people from vaccination. Across 43,099 vaccinated pregnancies, almost all with mRNA vaccines, early birth, small babies and stillbirth were not more common. Observational data, not a trial; vaccinated people differed in income and health, and although the study adjusted for this, the lower stillbirth rate may partly reflect such differences.
See the evidence
A population-based cohort of 85,162 live births and stillbirths in Ontario, Canada, from May to December 2021.
From the study: “Vaccination during pregnancy was not associated with any increased risk of overall preterm birth”
No added preterm risk
Fell DB et al. Risk of preterm birth, small for gestational age at birth, and stillbirth after covid-19 vaccination during pregnancy: population based retrospective cohort study. BMJ (Clinical research ed.). 2022.
From the study: “6.5% among vaccinated v 6.9% among unvaccinated”
No added preterm risk
Fell DB et al. Risk of preterm birth, small for gestational age at birth, and stillbirth after covid-19 vaccination during pregnancy: population based retrospective cohort study. BMJ (Clinical research ed.). 2022.
From the study: “No increase was found in risk of small for gestational age at birth (9.1% v 9.2%; 0.98, 0.93 to 1.03) or stillbirth (0.25% v 0.44%; 0.65, 0.51 to 0.84).”
No added preterm risk
Fell DB et al. Risk of preterm birth, small for gestational age at birth, and stillbirth after covid-19 vaccination during pregnancy: population based retrospective cohort study. BMJ (Clinical research ed.). 2022.
Pregnant women with COVID landed in intensive care far more often.
3.0× ICU riskAdjusted risk ratio, pregnant vs nonpregnant US women with symptomatic COVID
Among US women of reproductive age with symptomatic, lab-confirmed COVID, pregnant women were admitted to intensive care at 10.5 per 1,000 cases versus 3.9 per 1,000 for nonpregnant women. Deaths were 1.5 versus 1.2 per 1,000, which the CDC reported as a 70% higher risk of death linked to pregnancy.
Absolute risks were low, but pregnancy itself raised the danger of severe COVID, which is why health agencies treat pregnant women as a high-risk group who should seek prompt care for symptoms. Early-pandemic surveillance with pregnancy status missing for most cases; a later US study found the extra intensive-care risk tied to COVID at delivery shrank in the Omicron era.
See the evidence
CDC national surveillance of 409,462 US women aged 15–44 with symptomatic, lab-confirmed COVID, reported January to October 2020.
From the study: “Compared with nonpregnant women, pregnant women more frequently were admitted to an ICU (10.5 versus 3.9 per 1,000 cases; aRR = 3.0; 95% CI = 2.6–3.4)”
3.0× ICU risk
Zambrano LD et al. Update: Characteristics of Symptomatic Women of Reproductive Age with Laboratory-Confirmed SARS-CoV-2 Infection by Pregnancy Status - United States, January 22-October 3, 2020. MMWR. Morbidity and mortality weekly report. 2020.
From the study: “Thirty-four deaths (1.5 per 1,000 cases) were reported among 23,434 symptomatic pregnant women, and 447 (1.2 per 1,000 cases) were reported among 386,028 nonpregnant women”
3.0× ICU risk
Zambrano LD et al. Update: Characteristics of Symptomatic Women of Reproductive Age with Laboratory-Confirmed SARS-CoV-2 Infection by Pregnancy Status - United States, January 22-October 3, 2020. MMWR. Morbidity and mortality weekly report. 2020.
From the study: “reflecting a 70% increased risk for death associated with pregnancy”
3.0× ICU risk
Zambrano LD et al. Update: Characteristics of Symptomatic Women of Reproductive Age with Laboratory-Confirmed SARS-CoV-2 Infection by Pregnancy Status - United States, January 22-October 3, 2020. MMWR. Morbidity and mortality weekly report. 2020.
Placentas in COVID-linked stillbirths were massively damaged, pointing to oxygen starvation.
77.7% placenta damagedAverage placental tissue involved in 68 COVID-linked stillbirths and newborn deaths
Pathologists studied stillborn babies and newborn deaths whose mothers had COVID and whose placentas tested positive. A destructive inflammation called SARS-CoV-2 placentitis involved 77.7% of placental tissue on average. In 63% of the 30 autopsies, the only fetal finding was lack of oxygen, and there was no sign the virus in the baby caused death.
It suggests the main threat to the baby is destruction of the placenta, the organ that delivers oxygen, rather than the virus attacking the baby's own organs directly. A case series of selected deaths with no comparison group, so it cannot say how often this damage occurs among all infected pregnancies.
See the evidence
A review by 44 perinatal specialists in 12 countries of placentas and autopsies from 64 stillbirths and 4 newborn deaths after maternal COVID.
From the study: “Severe destructive placental disease from SARS-CoV-2 placentitis averaged 77.7% tissue involvement.”
77.7% placenta damaged
Schwartz DA et al. Placental Tissue Destruction and Insufficiency From COVID-19 Causes Stillbirth and Neonatal Death From Hypoxic-Ischemic Injury. Archives of pathology & laboratory medicine. 2022.
From the study: “The majority (19; 63%) of the 30 autopsies revealed no significant fetal abnormalities except for intrauterine hypoxia and asphyxia.”
77.7% placenta damaged
Schwartz DA et al. Placental Tissue Destruction and Insufficiency From COVID-19 Causes Stillbirth and Neonatal Death From Hypoxic-Ischemic Injury. Archives of pathology & laboratory medicine. 2022.
From the study: “There was no evidence that SARS-CoV-2 involvement of the fetus had a role in causing these deaths.”
77.7% placenta damaged
Schwartz DA et al. Placental Tissue Destruction and Insufficiency From COVID-19 Causes Stillbirth and Neonatal Death From Hypoxic-Ischemic Injury. Archives of pathology & laboratory medicine. 2022.
COVID vaccination did not lower couples' chances of getting pregnant.
No drop in fertilityPer-cycle chance of conceiving, vaccinated vs unvaccinated partners, US and Canada
Among 2,126 women in the US and Canada trying to conceive without fertility treatment, and their male partners, the chance of pregnancy each cycle was not appreciably different when either partner was vaccinated against COVID versus unvaccinated. A male partner's COVID infection was linked to a short-lived dip in that chance.
Fertility fears kept many young adults from vaccination. This study found no sign of harm from the vaccine, while infection in men may briefly lower fertility, which the authors suggest vaccination may help avoid. A self-reported online cohort of mostly white, well-off couples, and the estimate for men's recent infection was imprecise, so that dip is uncertain.
See the evidence
An internet-based North American cohort (PRESTO) of couples trying to conceive, enrolled December 2020 to September 2021 and followed to November 2021.
From the study: “COVID-19 vaccination was not appreciably associated with fecundability in either partner”
No drop in fertility
Wesselink AK et al. A Prospective Cohort Study of COVID-19 Vaccination, SARS-CoV-2 Infection, and Fertility. American journal of epidemiology. 2022.
Likely Long COVID showed no clear difference in early delivery
Among previously infected participants, the primary analysis did not establish a difference in early delivery between those with likely Long COVID and those without it.
Both preterm intervals included no difference; the additional analysis's comparison group is not available here. A blood-pressure disorder signal appeared only in sensitivity analysis.
Study details & original results
Metz, Torri D et al.. Pregnancy Outcomes in Individuals With Long COVID.. Obstetrics and gynecology. 2026.
No significant association between likely Long COVID and preterm delivery in the primary average treatment effect analysis among previously infected participants
No significant association between likely Long COVID and preterm delivery in the average treatment effect among the treated sensitivity analysis
ARR 1.11 95% CI: 0.60-2.06
Increased risk of hypertensive disorders of pregnancy with likely Long COVID, observed only in the average treatment effect among the treated sensitivity analysis
Preterm-birth findings differed by time since infection
A Swedish register cohort reported higher preterm-birth hazard within 2 weeks of infection; at 2 weeks or later, the estimate's interval included no difference.
The early higher hazard remained after excluding women admitted for SARS-CoV-2 infection. Comparison groups are not available in this summary. The source notice records a numerical correction and a withheld vaccination finding because intervals disagree.
Study details & original results
Berglin, Lisa et al.. Severe acute respiratory syndrome coronavirus 2 and preterm birth, clinical implications-A register-based cohort study from Sweden.. Pregnancy (Hoboken, N.J.). 2025. [Source notice: Correction 2026-01-12 (10.1002/pmf2.70206) replaced the initial 25% infection sample with the full population and corrected numerical content and figures. The vaccination finding is withheld because the current abstract and Results disagree on its confidence interval.]
Preterm birth within 2 weeks of a positive SARS-CoV-2 test at 22-27, 28-31, and 32-36 gestational weeks, respectively; gestational age at infection significantly interacted with the hazard ratio.
aHR 6.0, 6.1, and 3.2; interaction p=0.047 95% CI: 3.9-9.2, 4.4-8.4, and 2.7-3.7, respectively
Preterm-birth hazard 2 weeks or more after the start of SARS-CoV-2 infection.
aHR 1.2; p=0.016 95% CI: 1.0-1.4
Preterm birth within 2 weeks of infection after excluding women admitted for SARS-CoV-2 infection.
COVID was linked to maternal and fetal deaths in a US study
In a US study, COVID-19 was associated with higher odds of in-hospital death across the reported variant periods, and of fetal death at 20 or more weeks during Pre-Alpha and Delta.
The in-hospital death finding concerns delivery-related hospitalizations. Comparison groups and absolute event rates are not available in this summary; these associations do not establish an individual's risk.
Study details & original results
Kilday, Deborah et al.. Association between COVID-19 by variant period and delivery-related outcomes in the United States.. PloS one. 2026.
Adjusted odds of in-hospital mortality associated with COVID-19 during the Delta period among delivery-related hospitalizations
aOR 29.47; adjusted p<.001
Adjusted odds of in-hospital mortality associated with COVID-19 during the first Omicron period among delivery-related hospitalizations
aOR 3.55; adjusted p=.04
Adjusted odds of in-hospital mortality associated with COVID-19 during the Alpha period among delivery-related hospitalizations
aOR 13.03; adjusted p<.001
Adjusted odds of in-hospital mortality associated with COVID-19 during the Pre-Alpha period among delivery-related hospitalizations
aOR 13.11; adjusted p<.001
Adjusted odds of fetal death at 20 or more weeks associated with maternal COVID-19 during the Delta period
aOR 3.37; p<.001 CI: 2.95-3.84
Adjusted odds of fetal death at 20 or more weeks associated with maternal COVID-19 during the Pre-Alpha period
Pandemic-era birth outcomes moved in different directions
The review reported fewer preterm births during the pandemic than before it. Newborn deaths fell in high-income countries, while stillbirths rose in low- and middle-income countries.
The greatest reported preterm reduction was below 28 weeks in high-income countries. The country-specific findings' comparison groups are not available in this summary; these are different outcomes and populations, not an effect of infection.
Study details & original results
Peart, S R et al.. Preterm Birth and Perinatal Mortality During the COVID-19 Pandemic Period: A Systematic Review and Meta-Analysis.. Journal of paediatrics and child health. 2026.
Preterm births decreased during pandemic period compared to pre-pandemic
OR 0.95 95% CI 0.94-0.97
Greatest reduction for births <28 weeks' gestation in high-income countries
OR 0.92 95% CI 0.88-0.96
Neonatal deaths reduced in high-income countries during pandemic
OR 0.78 95% CI 0.64-0.95
Stillbirth rates increased in low- and middle-income countries during pandemic
No significant association between likely Long COVID and preterm delivery in the primary average treatment effect analysis among previously infected participants
Increased risk of hypertensive disorders of pregnancy with likely Long COVID, observed only in the average treatment effect among the treated sensitivity analysis
Berglin, Lisa et al.. Severe acute respiratory syndrome coronavirus 2 and preterm birth, clinical implications-A register-based cohort study from Sweden.. Pregnancy (Hoboken, N.J.). 2025. [Source notice: Correction 2026-01-12 (10.1002/pmf2.70206) replaced the initial 25% infection sample with the full population and corrected numerical content and figures. The vaccination finding is withheld because the current abstract and Results disagree on its confidence interval.]
Preterm birth within 2 weeks of a positive SARS-CoV-2 test at 22-27, 28-31, and 32-36 gestational weeks, respectively; gestational age at infection significantly interacted with the hazard ratio.
Added
aHR 6.0, 6.1, and 3.2; interaction p=0.04795% CI: 3.9-9.2, 4.4-8.4, and 2.7-3.7, respectivelySource [3]
Preterm-birth hazard 2 weeks or more after the start of SARS-CoV-2 infection.
Peart, S R et al.. Preterm Birth and Perinatal Mortality During the COVID-19 Pandemic Period: A Systematic Review and Meta-Analysis.. Journal of paediatrics and child health. 2026.
Browse the 12 original sourcesThe complete bibliography behind this monitor.
[1]
Peart, S R et al.. Preterm Birth and Perinatal Mortality During the COVID-19 Pandemic Period: A Systematic Review and Meta-Analysis.. Journal of paediatrics and child health. 2026.
Berglin, Lisa et al.. Severe acute respiratory syndrome coronavirus 2 and preterm birth, clinical implications-A register-based cohort study from Sweden.. Pregnancy (Hoboken, N.J.). 2025. [Source notice: Correction 2026-01-12 (10.1002/pmf2.70206) replaced the initial 25% infection sample with the full population and corrected numerical content and figures. The vaccination finding is withheld because the current abstract and Results disagree on its confidence interval.]
Remoué, Annabelle et al.. Omicron SARS-CoV-2 maternal infection is associated with favorable fetomaternal outcomes and fewer placental vascular malperfusion lesions compared with previous variants.. AJOG global reports. 2026.
DeSisto CL et al. Risk for Stillbirth Among Women With and Without COVID-19 at Delivery Hospitalization - United States, March 2020-September 2021. MMWR. Morbidity and mortality weekly report. 2021.
Thoma ME et al. Changes in Pregnancy-Related Mortality Associated With the Coronavirus Disease 2019 (COVID-19) Pandemic in the United States. Obstetrics and gynecology. 2023.
Fell DB et al. Risk of preterm birth, small for gestational age at birth, and stillbirth after covid-19 vaccination during pregnancy: population based retrospective cohort study. BMJ (Clinical research ed.). 2022.
Zambrano LD et al. Update: Characteristics of Symptomatic Women of Reproductive Age with Laboratory-Confirmed SARS-CoV-2 Infection by Pregnancy Status - United States, January 22-October 3, 2020. MMWR. Morbidity and mortality weekly report. 2020.
Schwartz DA et al. Placental Tissue Destruction and Insufficiency From COVID-19 Causes Stillbirth and Neonatal Death From Hypoxic-Ischemic Injury. Archives of pathology & laboratory medicine. 2022.
Read each original paper for its complete methods, population and limitations. Different studies can ask different questions and report different kinds of results. Dates marked “added” describe when a finding entered this monitor, not when the study was published or clinically reviewed.
Download the findings and bibliography displayed in this page snapshot. Values and confidence intervals remain as reported text; this is not a pooled estimate or a systematic review. Product-label observations and editorial takeaways are excluded.
These findings may omit evidence or contain errors and have not been reviewed by a clinician. A citation or download does not establish source verification. Read the original studies for their methods and limitations.
The October 2026 COVID citation audit found errors in this collection. These downloads may still contain affected findings and bibliography entries. Read the correction record before using them.
“Added” dates record entry into the monitor, not publication or clinical review. A null original acquisition or derivation means its historical record is unknown; a current record or verification has its own observation time. The SHA-256 snapshot identifier binds the downloadable public fields. CSV includes finding rows and bibliography-only source rows; JSON includes both lists. Spreadsheet-sensitive CSV cells begin with an apostrophe for safety; JSON preserves the original text.
For attribution, cite ModernDoc and the page URL, data update date and snapshot identifier in the download. Original studies retain their own rights; this download does not grant a licence to their full text.