Last reviewed: September 21. 2022
Recommendation:
- Gestational age should be calculated using a person’s last menstrual period (LMP) combined with physical examination.
- Routine use of ultrasound for gestational age determination is not necessary.
Strength of recommendation: Strong
Quality of evidence: Very low
Importance of accurate gestational dating
Errors in gestational dating can increase the risks associated with abortion. If gestational age is underestimated prior to dilatation and evacuation (D&E), providers may not have the experience and equipment to complete the procedure safely. Accurate assessment of gestational age enables providers to determine whether the facility is equipped to provide the requested service and refer to another facility if necessary.
Dating
Gestational age assessment using bimanual examination and LMP is well established during prenatal care, as is the use of ultrasound. No prospective trials have compared the accuracy of different methods of gestational dating prior to abortion at or after 13 weeks, however, in a retrospective cohort of 2,223 women undergoing abortion at or after 13 weeks gestation in Nepal, gestational age assessed by measuring fetal foot length after pregnancy expulsion was highly correlated with ultrasonography (81%), physical exam (77%) and LMP (72%) assessments (Kapp et al., 2020). In the United States, virtually all providers use ultrasound for gestational age assessment after 12 weeks gestation, but data are lacking from other country contexts.
Prior to medical abortion, gestational age can be estimated using the first day of a woman’s LMP and a physical examination that includes bimanual and abdominal examination (Nautiyal et al., 2015; Ngoc et al., 2011; Royal College of Obstetricians and Gynaecologists [RCOG], 2022; World Health Organization [WHO], 2022). Measuring fundal height, as in routine obstetric care, can provide additional information as the pregnancy advances (Pugh et al., 2018). Ultrasound can be used to confirm gestational age if the LMP and clinical examination are discordant or if there is uncertainty about gestational age but is not required prior to medical abortion.
In published studies of D&E, including reports of implementation of D&E programs (Castleman et al., 2006; Jacot et al., 1993), ultrasound has been routinely used to establish or confirm gestational age prior to D&E. However, one published report (Altman et al., 1985), unpublished programmatic data (A. Edelman, personal communication, January 12, 2018) and expert opinion support use of LMP and physical examination for gestational age assessment, with use of ultrasound as needed (RCOG, 2022; WHO, 2022). If ultrasound is used, biparietal diameter is a simple and accurate method to confirm gestational age (Goldstein & Reeves, 2009). A femur length measurement can be used to confirm the biparietal diameter or used if there are technical difficulties in obtaining a biparietal measurement.
People who present with fetal demise, incomplete abortion or for postabortion care may have discordant LMP dates and uterine size; they should be treated according to uterine size (RCOG, 2022; WHO, 2022).
After the abortion, clinicians can confirm gestational age by comparing actual fetal measurements (fetal foot length) to the expected gestational age (Drey et al., 2005; Mokkarala et al., 2020). This comparison provides feedback regarding the accuracy of pre-procedure dating estimates. Pregnancy dating tools, such as fetal measurements, are included in Ipas’s Dilatation & Evacuation (D&E) Reference Guide: Induced Abortion and Postabortion Care at or After 13 Weeks Gestation, page 38 (2017), and Medical Abortion Reference Guide: Induced Abortion and Postabortion Care at or After 13 Weeks Gestation, page 30 (2017).
References
Altman, A. M., Stubblefield, P. G., Schlam, J. F., Loberfeld, R., & Osanthanondh, R. (1985). Midtrimester abortion with laminaria and vacuum evacuation on a teaching service. The Journal of Reproductive Medicine, 30(8), 601-606.
Castleman, L. D., Oanh, K. T. H., Hyman, A. G., Thuy, L. T. T., & Blumenthal, P. D. (2006). Introduction of the dilation and evacuation procedure for second-trimester abortion in Vietnam using manual vacuum aspiration and buccal misoprostol. Contraception, 74, 272-276.
Drey, E. A., Kang, M. S., McFarland, W., & Darney, P. D. (2005). Improving the accuracy of fetal foot length to confirm gestational duration. Obstetrics & Gynecology, 105(4), 773-778.
Edelman, A., & Kapp, N. (2017). Dilatation & Evacuation (D&E) Reference Guide: Induced abortion and postabortion care at or after 13 weeks gestation. Chapel Hill, NC: Ipas.
Edelman, A., & Mark, A. (2017). Medical Abortion Reference Guide: Induced abortion and postabortion care at or after 13 weeks gestation. Chapel Hill, NC: Ipas.
Goldstein, S. R., & Reeves, M. F. (2009). Clinical assessment and ultrasound in early pregnancy. In M. Paul, E. S. Lichtenberg, L. Borgatta, D. A. Grimes, P. G. Stubblefield & M. D. Creinin (Eds.), Management of unintended and abnormal pregnancy: Comprehensive abortion care. Oxford: Wiley-Blackwell.
Jacot, F. R. M., Poulin, C., Bilodeau, A. P., Morin, M., Moreau, S., Gendron, F., & Mercier, D. (1993). A five-year experience with second-trimester induced abortions: No increase in complication rate as compared to the first trimester. American Journal of Obstetrics & Gynecology, 168, 633-637.
Kapp, N., Griffin, R., Bhattarai, N., & Dangol, D.S. (2020). Does prior ultrasonography affect the safety of induced abortion at or after 13 weeks’ gestation? A retrospective study. Acta Obstetricia et Gynecologica Scandinavica, doi: 10.1111/aogs.14040. Epub ahead of print. PMID: 33185906.
Kulier, R., & Kapp, N. (2011). Comprehensive analysis of the use of pre-procedure ultrasound for first- and second-trimester abortion. Contraception, 83(1), 30-33.
Mokkarala, S., Creinin, M. D., Wilson, M. D., Yee, N. S., & Hou, M. Y. (2020). Comparing preoperative dating and postoperative dating for second-trimester surgical abortions. Contraception, 101(1), 5-9.
Nautiyal, D., Mukherjee, K., Perhar, I., & Banerjee, N. (2015). Comparative study of misoprostol in first and second trimester abortions by oral, sublingual, and vaginal routes. The Journal of Obstetrics and Gynecology of India, 64(4), 246-250.
Pugh, S. J., Ortega-Villa, A. M., Grobman, W., Newman, R. B., Owen, J., Wing, D. A., . . . Grantz, K. L. (2018). Estimating gestational age at birth from fundal height and additional anthropometrics: a prospective cohort study. BJOG: An International Journal of Obstetrics and Gynaecology, 125(11), 1397-1404.
Ngoc, N. T. N., Shochet, T., Raghavan, S., Blum, J., Nga, N. T. B., Minh, N. T. H., & Winikoff, B. (2011) Mifepristone and misoprostol compared with misoprostol alone for second-trimester abortion: A randomized controlled trial. Obstetrics & Gynecology, 118(3), 601-608.
Royal College of Obstetricians and Gynaecologists. (2022). Best practice in abortion care. London: Royal College of Obstetricians and Gynaecologists.
Royal College of Obstetricians and Gynaecologists. (2022). Best practice in postabortion care. London: Royal College of Obstetricians and Gynaecolgists.
White, K. O., Jones, H. E, Shorter, J., Norman, W. V., Guilbert, E., Lichtenberg, E. S., & Paul, M. (2018). Second-trimester surgical abortion practices in the United States. Contraception, 98, 95-99.
World Health Organization. (2022). Abortion Care Guideline. Geneva: World Health Organization.