What is the normal proportion of the weight of the placenta to the weight of the baby at term?

Appeared in: DSSSB October 2024

Explanation

At term, a healthy placenta weighs approximately 470-500 grams.
A healthy full-term fetus weighs around 3000 grams (3 kg).
The ratio of the placenta's weight to the baby's weight is therefore approximately 500g to 3000g.
This proportion simplifies to a 1:6 ratio.

Option A: A 1:2 ratio would mean the placenta weighs half as much as the baby (e.g., 1500g for a 3000g baby). This indicates a severely and abnormally large placenta (placentomegaly), which is not normal.
Option C: A 1:4 ratio suggests the placenta weighs a quarter of the baby's weight (e.g., 750g for a 3000g baby). This is heavier than the normal average and would be considered placentomegaly, often associated with maternal or fetal complications.
Option D: A 1:3 ratio implies the placenta weighs one-third of the baby's weight (e.g., 1000g for a 3000g baby). This represents a significantly large placenta and is associated with pathological conditions, not a normal term pregnancy.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Feto-placental weight ratio at term as background academic context rather than a clinical decision trigger.
The feto-placental weight ratio is an important indicator of placental efficiency and overall pregnancy health. Nurses and midwives inspect the placenta after delivery for size, shape, and completeness.
An abnormal ratio can alert the clinical team to potential underlying maternal or neonatal issues that require further investigation, such as infection, maternal diabetes, or fetal growth restriction.
What if? If the ratio was 1:4, this would indicate an abnormally large placenta (placentomegaly). The nurse should review the maternal history for risk factors like diabetes or anemia and closely monitor the neonate for complications such as hypoglycemia or respiratory distress.

How to Approach the Question

This is a factual recall question testing knowledge of normal physiological parameters in pregnancy.
First, recall the average weight of a healthy placenta at full term, which is around 500 grams.
Next, recall the average weight of a healthy baby at full term, which is around 3000 grams.
Set up the proportion as Placenta Weight : Baby Weight, which is 500 : 3000.
Simplify this ratio by dividing both sides by 500. This gives you 1 : 6.
Select the option that matches this calculated ratio.

Concept Tested & Keywords

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E6 Obstetrics Williams p. 9-26

E6 Anatomy Grays 43e Vol 1 Part 3 p. 10-12

Practise the full DSSSB October 2024

Attempt every question from this paper in a timed mock, then review the full solution for each one.