MD Notes

creation date: 2026-10-09 12:55
tags: Interventions

Prenatal Schedule

Background

Prenatal schedule, or antenatal schedule, refers to the timing of testing, immunizations, and other components of care prior to delivery.

Schedule

0-13 Weeks

At the first appointment (usually presenting after amenorrhea / positive pregnancy test).

Bloodwork

  • CBC (Hb, Hct)
  • ABO and Rh
  • Rubella
  • Hepatitis B
  • Hepatitis C
  • STI
  • HIV

Urine

  • Confirms pregnancy with bHCG (present 8 days after conception)

Dating ultrasound

  • Identification of gestational age via crown-rump length
  • Before 14 wks gestation, precision of 5-7 days
  • Variability in estimates increase with with increasing duration of pregnancy
    • Use early scan for gestational age, and not redate in later trimesters
  • If crown-rump length >84mm (14 weeks gestation), may need to combine other methods such as:
    • Biparietal diameter (outer edge of proximal skull to inner edge of distal skull)
    • Head circumference
    • Abdominal circumerfence/aver abdominal diameter
    • Femoral diaphysis length (most accurate single method for gestation age in 3rd trimester)
  • Ultrasound-established dates replace menstrual dates when:

    • 5 days before 9 weeks

    • 7 days between 9-15 weeks

    • 10 days between 16-21 weeks

    • 14 days between 22-27 weeks

  • Ultrasound confirms menstrual dates if agreement is:
    • <7 days obtained by crown-rump length in first trimester
    • <14 days obtained by average of multiple methods between 14-27 weeks

eFTS

  • Screens for genetic conditions (Trisomy 21 and 18
  • Nuchal translucency
  • Protein measurement in blood

14-27 Weeks

Anatomy scan ultrasound (18-22 weeks)

  • EDC: estimated date of confinement (ie. due date)
  • EGA: estimated gestational age
  • Visibility of fetus
  • Amniotic fluid volume
  • Location of placenta (relative to internal os)
    • Low-lying: 1-20 mm to internal os
  • Appearance of fetus
  • Vessels
    • Normal = 3 (2 arteries, 1 vein)
    • 4 may signify GI or CV anomalies
  • Cord insertion
    • Transverse section view of abdomen for clean insertion of cord into abdominal wall
    • No evidence of associated mass (gastrochisis/comphalocele)

Glucose challenge test (24-28 weeks)

Bloodwork (24-28 weeks)

  • CBC for anemia

Tdap vaccination (28-32 weeks)

  • Often done with flu/COVID

28-40 Weeks

Routine appointments

  • Every 2 weeks, then weekly as due date approaches
  • Monitoring for diabetes, blood pressure, position of fetus

Antibody screening (28 weeks)

  • If Rh negative, RhD immune globulin given

Growth ultrasound (32, 36 week)

  • Indicated for size concerns or complications

GBS swab (35-37 weeks)
If positive, IV antibiotics start 4 hours prior to delivery:

  • First-line: penicillin G or ampicillin
  • Low risk penicillin allergy: cefazolin
  • High risk penicillin allergy: clindamycin (if susceptible) or vancomycin

Note: prophylaxis is not necessary if planned c-section before labour onset with intact amniotic membranes.

References

Tools / Guidelines

Additional Reading