TOPLINE: 

In a cohort of participants enrolled during early gestation, 1 in 4 reported bleeding during the first trimester, but bleeding alone was not associated with a risk for pregnancy loss. However, bleeding coupled with an ultrasound dating that lagged more than 5 days behind the last menstrual period dating was linked to an increased risk for pregnancy loss.

METHODOLOGY:

• Researchers recruited participants across three US states into a prospective pregnancy cohort, with enrollment in early gestation (median, 47 days); all participants underwent standardized first-trimester research ultrasonography (median, 58 days of gestation).
• The researchers followed up 5425 participants from enrollment through pregnancy outcome and surveyed bleeding episodes during the first trimester, capturing the timing and whether the bleeding was heavy or painful through self-reports; episodes ending at least 4 days before any pregnancy loss were analyzed.
• The researchers calculated gestational age based on the self-reported last menstrual period, and ultrasound lag was noted as ultrasound-based dating trailing last menstrual period dates by more than 5 days.
• They assessed the associations among bleeding in the first trimester, ultrasound findings, and pregnancy loss.

TAKEAWAY:

• Overall, 25.0% of participants reported bleeding during the first trimester, of whom 6.3% reported heavy bleeding and 29.0% reported painful bleeding; 12.0% of pregnancies ended in loss.
• Bleeding in the first trimester was not associated with a risk for pregnancy loss. Painful bleeding during the first trimester was also not associated with this risk.
• Among those with a first-trimester research ultrasound (n = 4906), 23.2% had ultrasound dates that lagged behind their last menstrual period dates by more than 5 days.
• Bleeding paired with an ultrasound lag of more than 5 days behind the last menstrual period dating was linked to an increased risk for pregnancy loss (hazard ratio, 2.72; 95% CI, 2.10-3.53).

IN PRACTICE:

"[The study] findings support that reassurance for most patients with first-trimester bleeding is appropriate, especially when ultrasound- and LMP [last menstrual period]-based dating agree. With these data, this research can provide patients with first-trimester bleeding with more tailored information about their risk of pregnancy loss," the authors wrote.

SOURCE:

The study was led by Alexandra C. Sundermann, MD, PhD, of the Department of Obstetrics and Gynecology, Institute for Medicine and Public Health, and the Department of Biomedical Informatics at the Vanderbilt University Medical Center in Nashville, Tennessee. It was published online on February 19, 2026, as a research letter in Obstetrics & Gynecology.

LIMITATIONS: 

The proportion of planned pregnancies was higher than that in the general population. Self-reported bleeding may introduce potential recall bias. Using the last menstrual period-based dating can be inaccurate, especially for individuals with irregular cycles or those who have recently used contraception.

DISCLOSURES:

The study was supported by grants from the National Institutes of Health (NIH) through Building Interdisciplinary Research Careers in Women's Health, the Eunice Kennedy Shriver National Institute of Child Health and Human Development of the NIH, and the American Water Works Association Research Foundation. No relevant conflicts of interest were disclosed by the authors.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.