Harvey's Garden

Prenatal care

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Gestational Age (GA) & Estimated Date of Delivery (EDD)

  • Gestational Age (GA): Time elapsed since the first day of the Last Menstrual Period (LMP). It is measured in weeks and is the standard way to date a pregnancy. Note that GA is about two weeks longer than the fetal age (time since conception).
  • Estimated Date of Delivery (EDD): Calculated as 40 weeks (280 days) from the first day of the LMP.

Methods for Determining GA and EDD

  • Naegele’s Rule: A common method to estimate the EDD, assuming a 28-day cycle.
    • Calculation: (LMP - 3 months) + 7 days + 1 year.
    • Example: If LMP is 11/1/2023, EDD is 8/8/2024.
  • Ultrasound: The most accurate method for determining GA, especially in the first trimester (up to 13 weeks and 6 days). It is particularly useful if the LMP is uncertain or cycles are irregular.

Fundal Height

  • Definition: The distance in centimeters from the pubic symphysis to the top of the uterine fundus. It’s a non-invasive screening tool to assess fetal growth.
  • Measurement:
    • Typically starts being measured around 20-24 weeks of gestation.
    • The patient should lie supine, and a tape measure is used for the measurement. An empty bladder is preferred as a full one can alter the measurement.

Correlation with Gestational Age

  • From 20-36 weeks: Fundal height in cm should roughly equal the GA in weeks (± 2 cm).
    • Example: At 28 weeks GA, the fundal height is expected to be around 26-30 cm.
  • Key Landmarks:
    • 12 weeks: Uterine fundus at the level of the pubic symphysis.
    • 16 weeks: Halfway between the pubic symphysis and the umbilicus.
    • 20 weeks: At the umbilicus.
    • 36 weeks: Reaches the xiphoid process (highest point).
    • >36 weeks: Fundal height may decrease as the fetal head engages in the pelvis (“lightening”).

Tip

先记住三个 12周 耻骨联合上2－3横指(常考) 28周 脐以上3横指 36周 剑突下2横指 然后以4周2个横指推算 24周就脐上1横指 20周就脐下1横指 16周未具体说明 在脐与耻骨联合之间 32周未具体说明 在脐与剑突直接 40周 因为38周羊水达到最大量1000ml 40周大概只有800ml 所以宫底可以在剑突下或者略高于剑突

Clinical Significance of Discrepancies

  • A discrepancy of > 2-3 cm from the expected GA warrants further investigation, usually with an ultrasound.
  • Fundal Height > GA (Large for Gestational Age - LGA):
    • Fetal macrosomia (often due to maternal diabetes).
    • Multiple gestations (e.g., twins).
    • Polyhydramnios (excess amniotic fluid).
    • Uterine fibroids.
    • Incorrect dating of pregnancy.
    • Maternal obesity can lead to less accurate measurements.
    • Breech presentation.
  • Fundal Height < GA (Small for Gestational Age - SGA):
    • Intrauterine Growth Restriction (IUGR).
    • Oligohydramnios (low amniotic fluid).
    • Incorrect dating of pregnancy.
    • Fetal descent into the pelvis.
    • Small maternal stature or strong abdominal muscles.
    • Transverse lie.

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