How is gestational age determined prior to tocolytic therapy in preterm labor?

Updated: May 04, 2021
  • Author: Michael G Ross, MD, MPH; Chief Editor: Carl V Smith, MD  more...
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One should always attempt to determine gestational age by first identifying the first day of the last menstrual period (LMP) and confirming it by one or more of the following:

  • Positive pregnancy test (home or clinic) prior to the expected date of the second missed period

  • Uterine size determined by bimanual examination prior to 12 weeks' gestation

  • Doppler fetal heart tones noted prior to 12 weeks' gestation

  • Ultrasonographic estimation of gestational age (ie, first trimester within 1 wk, second trimester within 2 wk, and third trimester within 3 wk)

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