Review note: AI-assisted draft independently checked against the cited sources by a separate AI reviewer. Not clinician-reviewed. Use with your course materials, supervised clinical training and current local policies.
Maternity questions often involve three different landmarks: the top of the uterus, the placental edge relative to the cervix, and the fetal part nearest the birth canal.
Anatomy connection: Open the pregnancy views in 3D
Fundal height by week
These are approximate teaching landmarks, not exact deadlines for every pregnancy.
| About | Expected landmark | 3D |
|---|---|---|
| 12 weeks | Fundus at or just above the symphysis pubis | view |
| 20 weeks | Fundus near the umbilicus | view |
| 36 weeks | Fundus high in the abdomen, near the xiphoid process | view |
The fundus may descend near term as the presenting part moves into the pelvis. OpenStax, Physiologic Changes and Second-Trimester Care
The centimeters-to-weeks rule
Measure from the upper border of the symphysis pubis to the uterine fundus. OpenStax gives a teaching estimate of gestational weeks ±2 cm from 20–36 weeks: at 28 weeks, approximately 26–30 cm. This is an estimate for screening, not proof of normal fetal growth or a precise method of dating pregnancy. OpenStax
Clinical schedules vary: NICE recommends routine measurements after 24 weeks in singleton pregnancies unless regular growth scans are being performed. Interpret serial measurements with the growth chart and clinical findings; concerning small or large measurements prompt ultrasound assessment. NICE, recommendations 1.2.30–1.2.32
High BMI, fibroids and multiple pregnancy can limit the usefulness of fundal-height measurements; ultrasound surveillance may be needed. Perinatal Institute, Fetal Growth Assessment
Placenta previa
Placenta previa involves the placenta reaching or covering the internal cervical opening. A low-lying placenta lies close to the opening without covering it; current RCOG guidance uses an edge-to-os distance of less than 20 mm after 16 weeks. These terms should not be treated as interchangeable. Follow-up imaging matters because many placentas identified as low-lying in midpregnancy are no longer low-lying later. RCOG, 2026 guideline, sections 2 and 5
- Typical presentation: painless vaginal bleeding, often bright red. Pain or contractions do not exclude previa.
- Urgency: bleeding with known or suspected previa requires immediate obstetric assessment, even when painless. Someone with a known low placenta should contact the hospital immediately for bleeding, contractions or pain.
- Examination precaution: avoid a digital vaginal examination when previa is suspected until ultrasound excludes it; do not perform one with known previa. This does not prohibit an appropriately performed transvaginal ultrasound or a clinician-directed speculum examination.
- Diagnosis: ultrasound establishes placental location. Transvaginal scanning is safe when appropriately performed and can clarify the relationship to the cervical opening.
See RCOG patient information and RCOG Antepartum Haemorrhage, sections 7.2–7.3.
Risk factors include previous previa, prior cesarean or other uterine surgery, smoking, assisted reproduction, multiparity and advanced maternal age. OpenStax, Conditions Limited to Pregnancy
Previa versus abruption
| Feature | Placenta previa | Placental abruption |
|---|---|---|
| Typical bleeding/pain pattern | Often painless bleeding; pain can occur | Often abdominal or back pain, with or without visible bleeding |
| Uterine findings | May be soft and nontender, but contractions can occur | Tenderness, frequent or prolonged contractions, or increased resting tone may occur |
These are pattern-recognition clues. Abruption can cause concealed hemorrhage, so visible blood loss can underestimate severity. Symptoms alone cannot safely establish or exclude either diagnosis. Assess maternal and fetal status urgently when bleeding or concerning pain occurs. OpenStax, Conditions Limited to Pregnancy
Breech presentation
In breech presentation, the buttocks or feet are nearest the cervix, with the head toward the upper uterus. Presentation describes the fetal part approaching the pelvis. OpenStax, Factors Influencing Labor and Birth
Breech is common earlier in pregnancy; about 3–4% of babies remain breech near term. Persistent breech around 36 weeks prompts discussion of external cephalic version and birth options with the obstetric team. Placenta previa is a reason not to perform external cephalic version. RCOG, Breech Baby at the End of Pregnancy
See breech presentation in 3D, then compare it with the head-down example at 36 weeks. The model illustrates a position; it does not imply every fetus is head-down at that gestation.
NCLEX-style reasoning
- At 24 weeks, fundal height is 23 cm: consistent with the teaching estimate. Review the growth trend and other findings before concluding that routine follow-up is sufficient.
- Painless bright red bleeding at 32 weeks: obtain urgent obstetric assessment and avoid a digital vaginal examination until previa is excluded.
- Fundus near the umbilicus: approximately 20 weeks is the classic landmark answer.
Educational content for exam preparation, written with AI using the linked sources. Not a substitute for clinical instruction or obstetric care protocols.