<p>Hypertensive disorders of pregnancy are defined according to office blood pressure (BP), yet out-of-office BP phenotypes may carry different prognostic implications. White-coat hypertension (WCH) is traditionally defined using 24-h ambulatory BP monitoring (ABPM) without considering nighttime BP, despite growing evidence supporting the prognostic relevance of nocturnal hypertension. This study aimed to evaluate the maternal–fetal risk associated with WCH according to the presence or absence of nighttime hypertension during the second half of pregnancy. We conducted a retrospective cohort study including high-risk pregnant women between 20 and 34 weeks of gestation referred for BP evaluation. Office BP and 24-h ABPM were performed using a standardized protocol. Women with office BP ≥ 140/90 mmHg were classified as having sustained hypertension, WCH without nighttime hypertension, or WCH with nighttime hypertension according to ambulatory blood pressure values across the different ABPM periods. The primary outcome was a composite of preeclampsia, eclampsia, or HELLP syndrome. Among 991 women evaluated, 79 met criteria for office hypertension. Of these, 40 had sustained hypertension, 28 had WCH without nighttime hypertension, and 11 had WCH with nighttime hypertension. The overall incidence of preeclampsia was 35%. Women with WCH and nighttime hypertension had a significantly higher risk of preeclampsia compared with those without nighttime hypertension, with a risk magnitude comparable to sustained hypertension. After multivariable adjustment, WCH with nighttime hypertension remained independently associated with preeclampsia (OR 11.95, <i>p</i> = 0.018). In conclusion, incorporating nighttime BP into the definition of WCH identifies a high-risk subgroup with prognostic implications similar to sustained hypertension. These findings support the routine use of ABPM, including nighttime BP assessment, in pregnant women with elevated office BP after 20 weeks of gestation.</p><p></p>