Accuracy of Menstrual History in Assessing Gestational Age Among Adolescents Seeking Abortion in England and Wales

Introduction

Determining how far along a pregnancy is—its gestational age—is critical to providing safe and effective abortion care. For adolescents under 16 seeking abortion services, identifying gestational age accurately ensures timely access to appropriate medical options and reduces risks of complications. Traditionally, gestational age is calculated based on the last menstrual period (LMP) reported by the patient, while ultrasonography provides a more objective measurement. However, accuracy concerns arise, especially in younger individuals who may have irregular cycles or recall difficulties. This article explores recent research conducted by the British Pregnancy Advisory Service (BPAS) in England and Wales that assesses the accuracy of menstrual history in estimating gestational age among adolescents and discusses implications for clinical practice and policy regarding no-test medication abortion.

Scientific and Clinical Evidence: What the Data Tell Us

Between May 2021 and April 2024, BPAS evaluated all abortion cases involving girls younger than 16 years old—referred to here as adolescents—to compare gestational age derived from self-reported LMP dates with that measured by ultrasound.

Among 1,555 adolescents who underwent abortion, 1,282 (82.4%) could provide an LMP date. On average, LMP dating tended to overestimate gestational age by approximately 3 days compared to ultrasound. This small discrepancy is clinically relevant when deciding eligibility for no-test medication abortion, which is typically allowed up to 69 days gestation. The study calculated the sensitivity (ability to detect those beyond the gestational limit) and specificity (ability to correctly identify those eligible) of LMP-based dating.

Using LMP alone, sensitivity to identify patients ineligible for no-test medication abortion was 86.6%, meaning about 13.4% of those truly ineligible would be missed based solely on LMP. Specificity was 78.8%, indicating a reasonable but not perfect ability to correctly classify eligible individuals. Importantly, only 2.8% of adolescents were false negatives—patients incorrectly deemed eligible who actually had gestation beyond the limit on ultrasound.

When additional menstrual history indicators (such as cycle regularity, date certainty, and symptoms) were incorporated into a composite screening tool, sensitivity improved significantly to 93.9%, reducing false negatives to 1.3%. However, specificity dropped to 54.2%, indicating many more adolescents would be unnecessarily referred for ultrasound scans despite being eligible.

Clinical Vignette

Consider “Emily,” a 15-year-old girl seeking abortion services. She recalls her last period occurred approximately 10 weeks ago, making her potentially eligible for no-test medication abortion. However, her menstrual cycles have been irregular. Using menstrual history alone, she might qualify. Yet an ultrasound shows she is at 11 weeks (77 days), beyond the typical no-test medication abortion window. If the clinic had relied solely on her LMP, Emily might have been offered medication abortion in a later gestation than guidelines safely allow. Conversely, overestimating gestational age might delay care unnecessarily.

Balancing Risks and Access: Implications for Practice and Policy

This study’s findings suggest that menstrual history offers robust sensitivity for detecting adolescents who should not receive medication abortion without further evaluation, with a low but nonzero risk of clinically significant misclassification. The addition of menstrual history indicators boosts safety but at the cost of increased ultrasound use, which may pose access and resource challenges.

In England and Wales, where adolescents already face disproportionate barriers to abortion care—including stigma, confidentiality concerns, and logistical hurdles—policy must weigh the risk of rare misestimations against maintaining easy access to early medication abortion. Over-reliance on ultrasound scans may delay care or create additional burdens.

Expert Insights and Recommendations

Dr. Helen McCulloch and Dr. Paula Lohr, lead authors of the study, emphasize that in adolescents, “menstrual dating is sufficiently accurate to guide safe no-test medication abortion in the vast majority of cases.” They advise that clinicians carefully assess menstrual history but consider ultrasound when menstrual dates are uncertain or cycles are irregular.

Recommendations for clinical practice include:

– Collecting comprehensive menstrual history alongside LMP date to improve accuracy.
– Prioritizing no-test medication abortion for those with clear menstrual dating within eligibility.
– Using ultrasound selectively to reduce delays and barriers.
– Providing adolescent-friendly care environments to support honest reporting and reduce stigma.

Conclusion

The BPAS evaluation reinforces that menstrual history is a reliable and practical tool for estimating gestational age among adolescents seeking abortion, supporting the safe expansion of no-test medication abortion access. Incorporating additional menstrual indicators improves safety further but may reduce specificity, leading to more ultrasounds. Careful clinical judgment and balanced policies are essential to optimize safety, access, and equity for adolescent patients. This evidence empowers providers and policymakers to make informed decisions about adolescent abortion care while respecting the unique challenges faced by this vulnerable group.

Funding and Clinical Trials

This study was conducted as part of BPAS quality assurance and research activity and did not receive specific external funding. There is no applicable clinical trial registration.

References

1. McCulloch H, Lohr PA. Accuracy of Menstrual History for Determining Gestational Age Among Adolescents Who Underwent Abortion in England and Wales. Obstet Gynecol. 2026 Mar;148(1):80-86. PMID: 41841735.

2. British Pregnancy Advisory Service. Clinical guidelines for abortion care. BPAS publications, 2024.

3. American College of Obstetricians and Gynecologists. Medication Abortion Up to 70 Days Gestation. ACOG Practice Bulletin, 2023.

—
For further reading on this topic, see related research on adolescent reproductive health and no-test medication abortion safety policies in peer-reviewed journals of obstetrics and gynecology.