Obstetric Definitions

Overview – Obstetric Definitions

Obstetric definitions underpin clear communication and safe clinical care during pregnancy and childbirth. This page covers core terminology related to births, miscarriages, fetal viability, perinatal periods, obstetric measurements, and delivery-related complications — all essential knowledge for final-year medical students preparing for both OSCEs and clinical placements.

Obstetrics definitions

Definition

Birth, Miscarriage & Abortion

  • Abortion: Termination of pregnancy (spontaneous or intentional) <20 weeks gestation or <500g.
  • Birth: Complete expulsion of the fetus ≥20 weeks gestation or ≥500g, regardless of placental expulsion.
  • Miscarriage:
    • Missed: Asymptomatic intrauterine fetal death (IUFD).
    • Threatened: Uterine bleeding ± contractions without cervical changes.
    • Inevitable: Uterine bleeding + contractions + cervical dilation (with labour).
    • Incomplete: Active miscarriage with retained products.
    • Complete: Inactive miscarriage with complete expulsion.

Neonatal and Perinatal Terms

  • Stillbirth: Birth of a fetus ≥20 weeks or ≥500g with no signs of life.
  • Early Neonatal Death: Death within 7 days of birth.
  • Late Neonatal Death: Death within 28 days of birth.
  • Perinatal Period: From 20 weeks gestation up to 28 days after birth.

Termination of Pregnancy (TOP)

  • Medical TOP: Mifepristone (RU486) followed by vaginal misoprostol 48 hrs later.
  • Surgical TOP: Dilation and curettage (D&C) or manual evacuation.

Gestational Timing

Trimesters

  • First Trimester (T1): 0–12 weeks
  • Second Trimester (T2): 13–28 weeks
  • Third Trimester (T3): 29–40 weeks

Gestational Age Definitions

  • Pre-term: <37 weeks
  • Term: 37–42 weeks
  • Post-term: >42 weeks

Counting Pregnancies

  • Gravidity: Total number of pregnancies (including current).
    • Nulligravida: Never pregnant
    • Primigravida: First pregnancy
  • Parity: Number of births ≥20 weeks (includes stillbirths).
    • Nullipara: Never carried to ≥20 weeks
    • Primipara: One birth ≥20 weeks
    • Multipara: >1 births ≥20 weeks
    • Grand multipara: ≥5 births
    • Great-grand multipara: ≥10 births

Twin Pregnancies

  • Chorionicity: Number of placentas
    • Monochorionic: One placenta
    • Dichorionic: Two placentas
  • Amnionicity: Number of amniotic sacs
    • Monoamniotic: One sac
    • Diamniotic: Two sacs

Antenatal Screening Anomalies

Growth Anomalies

  • CPD – Cephalopelvic Disproportion: Fetal head too large for maternal pelvis.
  • IUGR – Intrauterine Growth Restriction: Fetal growth fails to meet genetic potential (may show plateau or decline in velocity).
  • LBW:
    • <2500g = Low Birth Weight
    • <1500g = Very Low Birth Weight
    • <1000g = Extremely Low Birth Weight
  • SGA – Small for Gestational Age: Birth weight <10th percentile for gestational age. Not synonymous with IUGR.

Obstetric Bleeding

  • APH – Antepartum Haemorrhage: Vaginal bleeding after 24 weeks (includes during labour).
  • PPH – Postpartum Haemorrhage:
    • Primary: >500 mL blood loss within 24 hrs of delivery
    • Secondary: Vaginal bleeding within 6 weeks postpartum
  • Placenta Praevia: Placenta remains low-lying after 24 weeks.

Fetal Lie, Presentation & Position

  • Fetal Lie: Longitudinal, transverse, or oblique (will typically convert to longitudinal/transverse).
  • Fetal Presentation:
    • Cephalic/Breech (in longitudinal lie)
    • Shoulder (in transverse lie)
  • Fetal Attitude: Relation of fetal parts to each other (e.g., flexed, extended).
  • Fetal Position: Left or right side of the maternal pelvis.

Breech Subtypes

  1. Frank Breech: Buttocks first, legs extended (“pike”).
  2. Complete Breech: Buttocks first, legs flexed (“tuck”).
  3. Footling Breech: Foot first — one or both hips extended.

Membrane Rupture

  • SROM: Spontaneous Rupture of Membranes (± labour).
  • PROM: Premature rupture ≥37 weeks, ≥24 hrs before labour.
  • PPROM: Preterm PROM (<37 weeks, no labour).
  • ARM: Artificial rupture using an amniohook.

Labour and Delivery

  • Engagement: Descent of the presenting part into the pelvic brim (e.g. cephalic: 4/5 above brim = not yet engaged).
  • Labour:
    • Stage 1: Onset → Full cervical dilation
    • Stage 2: Full dilation → Birth
    • Stage 3: Birth → Placenta delivery
  • Delivery Modes:
    • SVD/SVB: Spontaneous vaginal delivery/birth
    • LUCS: Lower uterine caesarean section (transverse incision)
    • Classical C-section: Midline vertical incision
  • Trial of Scar / VBAC:
    • Trial of Scar: Attempt at vaginal birth after Caesarean.
    • VBAC: Successful vaginal birth after Caesarean.

Perinatal Complications

  • IRDS – Infant Respiratory Distress Syndrome:
    • AKA Hyaline Membrane Disease.
    • Due to surfactant deficiency or immature lung structure.
    • Presents with increased respiratory effort shortly after birth.

Summary – Obstetric Definitions

A solid understanding of obstetric definitions is essential for final-year medical students to interpret antenatal records, monitor labour progression, and communicate clearly across maternity teams. These terms are foundational to safe and effective obstetric care. For a broader context, see our Obstetrics Overview page.

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