Which of the following is true regarding relaxation of pelvic joints at term in pregnancy
The core concept here is probably related to the hormonal changes that occur to prepare the pelvis for childbirth. I remember that relaxin is a hormone involved in this process. Relaxin is produced by the corpus luteum and later by the placenta. It causes the ligaments and joints in the pelvis to relax, increasing their flexibility. This allows the pelvis to expand during labor, making delivery easier.
Now, looking at the options, I need to figure out which one is correct. The correct answer would mention relaxin as the key hormone. Let's think about the other options that might be present. For example, maybe someone might confuse it with estrogen or progesterone. Estrogen actually promotes bone density and might have the opposite effect, while progesterone causes smooth muscle relaxation but isn't specifically responsible for pelvic ligament relaxation. Another possible wrong option could be about mechanical changes, like the physical pressure of the fetus, but that's not the primary reason for joint relaxation.
So the correct answer should directly link relaxin to the relaxation of pelvic joints. The other options would be incorrect because they either attribute the process to the wrong hormone or a non-hormonal factor.
Clinical pearls: Remember that relaxin is crucial in pregnancy for pelvic ligament relaxation. Also, this might be a common exam question where other hormones are distractors. Another point is that relaxin can also affect other connective tissues, leading to joint laxity in general, which is why pregnant women might experience back pain or instability in other joints.
Putting this all together, the explanation should highlight relaxin's role, why other hormones aren't the main factors, and reinforce the importance of this hormone in the context of childbirth preparation. The clinical pearl helps students remember that relaxin is the key player here and differentiate it from other hormones like estrogen and progesterone.
**Core Concept** Relaxation of pelvic joints during term pregnancy is primarily mediated by **relaxin**, a hormone secreted by the corpus luteum and placenta. Relaxin increases ligamentous laxity and joint mobility, facilitating pelvic expansion for childbirth.
**Why the Correct Answer is Right** Relaxin acts on collagen fibers in pelvic ligaments, reducing their stiffness and enhancing flexibility. It also decreases myometrial contractility early in pregnancy but promotes cervical ripening later. This hormone is critical for adapting the pelvis to fetal passage during delivery.
**Why Each Wrong Option is Incorrect**
**Option A:** *Estrogen increases bone density* and promotes fetal growth but does not relax pelvic ligaments.
**Option B:** *Progesterone suppresses uterine contractions* but does not directly relax pelvic joints.
**Option C:** *Mechanical pressure from the fetus* may compress pelvic structures but does not cause physiological relaxation of joints.
**Clinical Pearl / High-Yield Fact** Relaxin levels peak in early pregnancy and again near term. Remember: **"Relaxin = Relax Pelvis"** for NEET/USMLE questions. Confusing it with progesterone’s role in maintaining pregnancy is a common exam trap.
**Correct Answer: C. Relaxin is responsible for ligamentous relaxation in the pelvis**