Objective To study the impact of the SARS-CoV-2 pandemic and the first lockdown in France on voluntary changes by pregnant women in the medical monitoring of their pregnancy. Study population Adult (>18 years old) pregnant women during the first lockdown (March-May 2020), living in France, and participating in an access panel of internet users. Design and Settings A cross-sectional study was conducted in July 2020 using a web-questionnaire completed by 500 pregnant women selected by quotas sampling (age group, socio-professional category, region of residence at the time of the lockdown, and parity). Methods A robust variance Poisson regression model was used to estimate adjusted prevalence ratios (aPRs). A manual stepwise descending approach was applied to obtain the final model. Main Outcome Measures Voluntary postponement or foregoing of pregnancy monitoring. Results Almost one women of five (23.4%) reported having voluntarily postponed or foregone at least one consultation or pregnancy check-up during the lockdown. Women who were professionally inactive (aPR=1.98, CI95%[1.24-3.16]), who had experienced serious disputes or violence during the lockdown (1.47, [1.00-2.16]), who felt they received little or no support (1.71, [1.07-2.71]), and those who changed health professionals during the lockdown (1.57, [1.04-2.36]) were all more likely to have voluntarily changed their pregnancy monitoring. Higher level of worry about the pandemic was associated with a lower probability of voluntarily changing pregnancy monitoring (0.66, [0.46 -0.96]). Conclusions Our results can guide prevention and support policies for pregnant women in the current and future pandemics. Financing Santé publique France