COVID-19 lockdowns had an impact on various factors affecting pregnancies.

Lockdown in the first trimester increased hypertensive disorders of pregnancy.

Lockdown in the first trimester lowered risk of small-for-gestational-age.

Lockdowns had a complex effect on the in-utero environment through the placenta.

To evaluate the effect of COVID-19 lockdown measures on the occurrence of hypertensive disorders of pregnancy and fetal growth restriction in a national pregnancy population.

This is a national registry-based quasi-experimental study, including singleton births ≥24 + 0 weeks from nulliparous women between 2016–2020. We evaluated the effect of gestational age upon entering the first nationwide lockdown period (March 9th–June 1st 2020) on outcome. This effect can be assumed to be unconfounded (a so-called quasi-experimental analysis), because this period was unexpected and implemented rapidly, minimizing anticipatory changes at population level.

Primary outcomes were hypertensive disorders of pregnancy (including pre-eclampsia) and small-for-gestational-age (birthweight <10th Hoftiezer percentile), as proxy for fetal growth restriction.

The analysis included 262,102 pregnancies. Compared to previous years, entering the lockdown in the first trimester was associated with an absolute +0.4% risk of hypertensive disorders of pregnancy (95%CI: +0.0% – +0.8%), +0.2% risk of pre-eclampsia (95%CI: +0.0% – +0.4%), but −0.5% risk of small-for-gestational-age (95%CI: −1.2 – –0.3). There was less evidence that other evaluated periods and trimesters were associated with the outcome.

Being exposed to COVID 19 lockdown was associated with a slight increase in hypertensive disorders of pregnancy, including pre-eclampsia, but a counterintuitive trend towards lower risk for small-for-gestational-age. Because the effect was most clear in the first trimester, the nationwide lockdown therefore seems to have a complex effect on the in-utero environment through the placenta.

© 2026 The Author(s). Published by Elsevier B.V. on behalf of International Society for the Study of Hypertension in Pregnancy.