MP CHO-2020
Obstetrics & Gynaecology
Hard
Which of the following Hormone does not cross the Placenta?
Appeared in: MP CHO-2020
Explanation
- Parathormone (PTH) and Calcitonin are classified as large peptide hormones.
- Due to their large molecular size and water-soluble nature, they are unable to diffuse across the lipid membranes of the placental barrier.
- The fetus develops its own parathyroid glands and thyroid C-cells to produce PTH and Calcitonin, respectively, ensuring independent regulation of its own calcium and phosphate metabolism, which is critical for bone development.
Why Other Options Were Wrong
- Option A: This option is incorrect because both Thyroxine and Steroids cross the placenta. Thyroxine is actively transported in limited amounts, and steroids, being lipid-soluble, diffuse readily.
- Option B: This option is incorrect because although Insulin (a peptide hormone) does not cross the placenta, Thyroxine does cross in limited amounts.
- Option C: This option is incorrect because while Insulin does not cross the placenta, Steroids are small, lipid-soluble molecules that cross with ease.
Related Visual
Clinical Relevance
- Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Placental transfer of hormones as background academic context rather than a clinical decision trigger.
- Understanding placental hormone transfer is vital for managing conditions like gestational diabetes. Since maternal insulin doesn't cross, the fetus exposed to high maternal glucose produces excess insulin, leading to macrosomia (large baby) and potential neonatal hypoglycemia.
- The administration of corticosteroids (a type of steroid) to mothers in preterm labor is a key nursing intervention. These steroids cross the placenta to accelerate fetal lung maturity, reducing the risk of respiratory distress syndrome in the newborn.
- What if? If a mother has untreated hypothyroidism, the limited transfer of maternal thyroxine in the first trimester can impair fetal brain development, as the fetal thyroid is not yet functional. This highlights the importance of screening and managing maternal thyroid status during pregnancy.
How to Approach the Question
- First, identify the core question, which asks which hormones do not cross the placenta. The negative framing is key.
- Recall the general principle of placental transport based on molecular properties: large, water-soluble molecules (like peptide/protein hormones) generally do not cross.
- Conversely, small, lipid-soluble molecules (like steroids) and some actively transported molecules (like thyroid hormones) do cross.
- Categorize the hormones in each option: Insulin, Parathormone, and Calcitonin are peptides. Steroids are lipids. Thyroxine is an amino acid derivative.
- Evaluate each pair based on the principle. Option A (Thyroxine, Steroids) both cross. Option B (Insulin, Thyroxine) has one that crosses. Option C (Insulin, Steroids) has one that crosses.
- Select the only pair where both hormones fit the 'do not cross' criteria, which is Parathormone and Calcitonin, both being large peptide hormones.
Concept Tested & Keywords
- Concept Tested: Placental transfer of hormones
- Stem keywords: Hormone, cross, Placenta
- Lead-in keywords: does not
- Negative lead-in flag: The question asks which hormones DO NOT cross the placenta.
Question ID
Qyb-sfC4pVIgU4ggPo8dyV
Reference Book
E6 Pharmacology KD Tripathi Essentials 9e Part 1 p. 282-284
E6 Obstetrics Williams p. 71-95
Practise the full MP CHO-2020
Attempt every question from this paper in a timed mock, then review the full solution for each one.
More Endocrinology in Relation to Reproduction Questions
- Before the placenta functions the corpus luteum is the primary source of synthesis of which of the following hormones:
- Which hormone is responsible for performing placental function during first 8-10 weeks of pregnancy?
- HCG secreted by?
- In the event of a successful conception, which hormone is primarily responsible for 'rescuing' the corpus luteum to maintain progesterone production?
- A hormone that prevents menstruation and maintains pregnancy by sustaining the function of the corpus luteum is?
- Chief source of progesterone during pregnancy is?
- Hormone responsible for ovulation is?
- Hormone responsible for ovum maturation?
- Placenta secretes all the following hormones, EXCEPT?
- Which of the following hormones is not produced by placenta?
More MP CHO-2020 Questions
- Data required to analyze the health status and define a community's health problem includes all except one?
- All of the following are included in ASHA's roles and responsibilities, except which option?
- The concept of Primary Health Care was recommended by which health committee?
- Which Gross Motor Development occurs in a 6-8 month old Infant?
- Flattening or falling of the child's weight curve is the earliest indication of what?
- What does ICDS stand for?
- What is the developmental stage of a child aged 3 to 6 years?
- What is a child who plays alone with toys and remains happy called?
- What is the recommended protein intake for an Adult Indian?
- What is the name of the disease caused by Vitamin-D deficiency in adults?